Linux Virtualization - Oct 2013 - [PATCH 0/3] x86: Support compiling out userspace I/O (iopl and ioperm)

This patch series makes it possible to compile out the iopl and ioperm system
calls, which allow privileged processes to request permission to directly poke
I/O ports from userspace.

Nothing on a modern Linux system uses these calls anymore, and anything new
should be using /dev/port instead, or better yet writing a driver.

Copying the bloat-o-meter stats from the final patch:

32-bit bloat-o-meter:
add/remove: 0/3 grow/shrink: 0/10 up/down: 0/-17681 (-17681)
function                                     old     new   delta
cpu_init                                     676     668      -8
ioperm_active                                 18       7     -11
init_task                                   1296    1284     -12
exit_thread                                  179      91     -88
ioperm_get                                   103      10     -93
__switch_to_xtra                             254     161     -93
sys_iopl                                     127       -    -127
SyS_iopl                                     127       -    -127
copy_thread                                  606     446    -160
vt_ioctl                                    4127    3919    -208
sys_ioperm                                   370       -    -370
init_tss                                    8576     384   -8192
doublefault_tss                             8576     384   -8192

64-bit bloat-o-meter:
add/remove: 0/4 grow/shrink: 2/9 up/down: 45/-9764 (-9719)
function                                     old     new   delta
cpu_init                                     958     995     +37
arch_align_stack                              78      86      +8
perf_event_exit_task                         525     517      -8
ioperm_active                                 17       8      -9
init_task                                   1968    1944     -24
stub_iopl                                     81       -     -81
ioperm_get                                   111      11    -100
__switch_to_xtra                             281     164    -117
exit_thread                                  212      92    -120
vt_ioctl                                    4432    4304    -128
sys_iopl                                     137       -    -137
SyS_iopl                                     137       -    -137
copy_thread                                  694     520    -174
sys_ioperm                                   473       -    -473
init_tss                                    8896     640   -8256

Josh Triplett (3):
  x86: process: Unify 32-bit and 64-bit copy_thread I/O bitmap handling
  x86: tss: Eliminate fragile calculation of TSS segment limit
  x86: Support compiling out userspace I/O (iopl and ioperm)

 arch/x86/Kconfig                      | 10 ++++
 arch/x86/include/asm/desc.h           | 11 +----
 arch/x86/include/asm/paravirt.h       |  2 +
 arch/x86/include/asm/paravirt_types.h |  2 +
 arch/x86/include/asm/processor.h      | 54 +++++++++++++++++---
 arch/x86/include/asm/syscalls.h       |  3 ++
 arch/x86/kernel/Makefile              |  3 +-
 arch/x86/kernel/cpu/common.c          | 12 +----
 arch/x86/kernel/entry_64.S            |  9 ++--
 arch/x86/kernel/paravirt.c            |  2 +
 arch/x86/kernel/process-io.h          | 93 +++++++++++++++++++++++++++++++++++
 arch/x86/kernel/process.c             | 34 ++-----------
 arch/x86/kernel/process_32.c          | 40 ++++-----------
 arch/x86/kernel/process_64.c          | 26 ++--------
 arch/x86/kernel/ptrace.c              |  8 +++
 arch/x86/xen/enlighten.c              |  4 ++
 drivers/tty/vt/vt_ioctl.c             |  2 +-
 kernel/sys_ni.c                       |  5 ++
 18 files changed, 206 insertions(+), 114 deletions(-)
 create mode 100644 arch/x86/kernel/process-io.h

-- 
1.8.4.rc3

The 32-bit and 64-bit versions of copy_thread have functionally
identical handling for copying the I/O bitmap, modulo differences in
error handling.  Clean up the error paths in both by moving the copy of
the I/O bitmap to the end, to eliminate the need to free it if
subsequent copy steps fail; move the resulting identical code to a
static inline in a common header.

Signed-off-by: Josh Triplett <josh at joshtriplett.org>
---
 arch/x86/kernel/process-io.h | 22 ++++++++++++++++++++++
 arch/x86/kernel/process_32.c | 29 ++++++++---------------------
 arch/x86/kernel/process_64.c | 26 +++++---------------------
 3 files changed, 35 insertions(+), 42 deletions(-)
 create mode 100644 arch/x86/kernel/process-io.h

diff --git a/arch/x86/kernel/process-io.h b/arch/x86/kernel/process-io.h
new file mode 100644
index 0000000..d884444
--- /dev/null
+++ b/arch/x86/kernel/process-io.h
@@ -0,0 +1,22 @@
+#ifndef _X86_KERNEL_PROCESS_IO_H
+#define _X86_KERNEL_PROCESS_IO_H
+
+static inline int copy_io_bitmap(struct task_struct *me,
+				 struct task_struct *p)
+{
+	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
+		p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
+						  IO_BITMAP_BYTES, GFP_KERNEL);
+		if (!p->thread.io_bitmap_ptr) {
+			p->thread.io_bitmap_max = 0;
+			return -ENOMEM;
+		}
+		set_tsk_thread_flag(p, TIF_IO_BITMAP);
+	} else {
+		p->thread.io_bitmap_ptr = NULL;
+	}
+
+	return 0;
+}
+
+#endif /* _X86_KERNEL_PROCESS_IO_H */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 884f98f..e86028b 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -56,6 +56,8 @@
 #include <asm/debugreg.h>
 #include <asm/switch_to.h>
 
+#include "process-io.h"
+
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
 asmlinkage void ret_from_kernel_thread(void)
__asm__("ret_from_kernel_thread");
 
@@ -135,7 +137,6 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 {
 	struct pt_regs *childregs = task_pt_regs(p);
 	struct task_struct *tsk;
-	int err;
 
 	p->thread.sp = (unsigned long) childregs;
 	p->thread.sp0 = (unsigned long) (childregs+1);
@@ -167,36 +168,22 @@ int copy_thread(unsigned long clone_flags, unsigned long
sp,
 	task_user_gs(p) = get_user_gs(current_pt_regs());
 
 	p->fpu_counter = 0;
-	p->thread.io_bitmap_ptr = NULL;
 	tsk = current;
-	err = -ENOMEM;
 
 	memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 
-	if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
-		p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
-						IO_BITMAP_BYTES, GFP_KERNEL);
-		if (!p->thread.io_bitmap_ptr) {
-			p->thread.io_bitmap_max = 0;
-			return -ENOMEM;
-		}
-		set_tsk_thread_flag(p, TIF_IO_BITMAP);
-	}
-
-	err = 0;
-
 	/*
 	 * Set a new TLS for the child thread?
 	 */
-	if (clone_flags & CLONE_SETTLS)
+	if (clone_flags & CLONE_SETTLS) {
+		int err;
 		err = do_set_thread_area(p, -1,
 			(struct user_desc __user *)childregs->si, 0);
-
-	if (err && p->thread.io_bitmap_ptr) {
-		kfree(p->thread.io_bitmap_ptr);
-		p->thread.io_bitmap_max = 0;
+		if(err)
+			return err;
 	}
-	return err;
+
+	return copy_io_bitmap(tsk, p);
 }
 
 void
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index bb1dc51..6e680ad 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -50,6 +50,8 @@
 #include <asm/debugreg.h>
 #include <asm/switch_to.h>
 
+#include "process-io.h"
+
 asmlinkage extern void ret_from_fork(void);
 
 asmlinkage DEFINE_PER_CPU(unsigned long, old_rsp);
@@ -154,7 +156,6 @@ static inline u32 read_32bit_tls(struct task_struct *t, int
tls)
 int copy_thread(unsigned long clone_flags, unsigned long sp,
 		unsigned long arg, struct task_struct *p)
 {
-	int err;
 	struct pt_regs *childregs;
 	struct task_struct *me = current;
 
@@ -164,7 +165,6 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 	p->thread.usersp = me->thread.usersp;
 	set_tsk_thread_flag(p, TIF_FORK);
 	p->fpu_counter = 0;
-	p->thread.io_bitmap_ptr = NULL;
 
 	savesegment(gs, p->thread.gsindex);
 	p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs;
@@ -192,23 +192,13 @@ int copy_thread(unsigned long clone_flags, unsigned long
sp,
 	if (sp)
 		childregs->sp = sp;
 
-	err = -ENOMEM;
 	memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 
-	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
-		p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
-						  IO_BITMAP_BYTES, GFP_KERNEL);
-		if (!p->thread.io_bitmap_ptr) {
-			p->thread.io_bitmap_max = 0;
-			return -ENOMEM;
-		}
-		set_tsk_thread_flag(p, TIF_IO_BITMAP);
-	}
-
 	/*
 	 * Set a new TLS for the child thread?
 	 */
 	if (clone_flags & CLONE_SETTLS) {
+		int err;
 #ifdef CONFIG_IA32_EMULATION
 		if (test_thread_flag(TIF_IA32))
 			err = do_set_thread_area(p, -1,
@@ -217,16 +207,10 @@ int copy_thread(unsigned long clone_flags, unsigned long
sp,
 #endif
 			err = do_arch_prctl(p, ARCH_SET_FS, childregs->r8);
 		if (err)
-			goto out;
-	}
-	err = 0;
-out:
-	if (err && p->thread.io_bitmap_ptr) {
-		kfree(p->thread.io_bitmap_ptr);
-		p->thread.io_bitmap_max = 0;
+			return err;
 	}
 
-	return err;
+	return copy_io_bitmap(me, p);
 }
 
 static void
-- 
1.8.4.rc3

__set_tss_desc has a complex calculation of the TSS segment limit,
duplicating the quirky details of the I/O bitmap array length, and
requiring a complex comment to explain.  Replace that calculation with a
simpler one based on the offsetof the "stack" field that follows the
array.

That then removes the last use of IO_BITMAP_OFFSET, so delete it.

Signed-off-by: Josh Triplett <josh at joshtriplett.org>
---
 arch/x86/include/asm/desc.h      | 11 +----------
 arch/x86/include/asm/processor.h |  3 ++-
 2 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index b90e5df..17ac92f 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -177,16 +177,7 @@ static inline void __set_tss_desc(unsigned cpu, unsigned
int entry, void *addr)
 	struct desc_struct *d = get_cpu_gdt_table(cpu);
 	tss_desc tss;
 
-	/*
-	 * sizeof(unsigned long) coming from an extra "long" at the end
-	 * of the iobitmap. See tss_struct definition in processor.h
-	 *
-	 * -1? seg base+limit should be pointing to the address of the
-	 * last valid byte
-	 */
-	set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS,
-			      IO_BITMAP_OFFSET + IO_BITMAP_BYTES +
-			      sizeof(unsigned long) - 1);
+	set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS, TSS_LIMIT);
 	write_gdt_entry(d, entry, &tss, DESC_TSS);
 }
 
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 987c75e..03d3003 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -259,9 +259,10 @@ struct x86_hw_tss {
 #define IO_BITMAP_BITS			65536
 #define IO_BITMAP_BYTES			(IO_BITMAP_BITS/8)
 #define IO_BITMAP_LONGS			(IO_BITMAP_BYTES/sizeof(long))
-#define IO_BITMAP_OFFSET		offsetof(struct tss_struct, io_bitmap)
 #define INVALID_IO_BITMAP_OFFSET	0x8000
 
+#define TSS_LIMIT	(offsetof(struct tss_struct, stack) - 1)
+
 struct tss_struct {
 	/*
 	 * The hardware state:
-- 
1.8.4.rc3

On the vast majority of modern systems, no processes will use the
userspsace I/O syscalls, iopl and ioperm.  Add a new config option,
CONFIG_X86_IOPORT, to support configuring them out of the kernel
entirely.  Since these syscalls only exist to support rare legacy
userspace programs, X86_IOPORT does not depend on EXPERT, though it does
still default to y.

In addition to saving a significant amount of space, this also reduces
the size of several major kernel data structures, drops a bit of code
from several task-related hot paths, and reduces the attack surface of
the kernel.

All of the task-related code dealing with userspace I/O permissions now
lives in process-io.h as several new inline functions, which become
no-ops when CONFIG_X86_IOPORT.

bloat-o-meter shows a net reduction of 17681 bytes on 32-bit and 9719
bytes on 64-bit:

32-bit bloat-o-meter:
add/remove: 0/3 grow/shrink: 0/10 up/down: 0/-17681 (-17681)
function                                     old     new   delta
cpu_init                                     676     668      -8
ioperm_active                                 18       7     -11
init_task                                   1296    1284     -12
exit_thread                                  179      91     -88
ioperm_get                                   103      10     -93
__switch_to_xtra                             254     161     -93
sys_iopl                                     127       -    -127
SyS_iopl                                     127       -    -127
copy_thread                                  606     446    -160
vt_ioctl                                    4127    3919    -208
sys_ioperm                                   370       -    -370
init_tss                                    8576     384   -8192
doublefault_tss                             8576     384   -8192

64-bit bloat-o-meter:
add/remove: 0/4 grow/shrink: 2/9 up/down: 45/-9764 (-9719)
function                                     old     new   delta
cpu_init                                     958     995     +37
arch_align_stack                              78      86      +8
perf_event_exit_task                         525     517      -8
ioperm_active                                 17       8      -9
init_task                                   1968    1944     -24
stub_iopl                                     81       -     -81
ioperm_get                                   111      11    -100
__switch_to_xtra                             281     164    -117
exit_thread                                  212      92    -120
vt_ioctl                                    4432    4304    -128
sys_iopl                                     137       -    -137
SyS_iopl                                     137       -    -137
copy_thread                                  694     520    -174
sys_ioperm                                   473       -    -473
init_tss                                    8896     640   -8256

Signed-off-by: Josh Triplett <josh at joshtriplett.org>
---
 arch/x86/Kconfig                      | 10 +++++
 arch/x86/include/asm/paravirt.h       |  2 +
 arch/x86/include/asm/paravirt_types.h |  2 +
 arch/x86/include/asm/processor.h      | 51 +++++++++++++++++++++----
 arch/x86/include/asm/syscalls.h       |  3 ++
 arch/x86/kernel/Makefile              |  3 +-
 arch/x86/kernel/cpu/common.c          | 12 +-----
 arch/x86/kernel/entry_64.S            |  9 +++--
 arch/x86/kernel/paravirt.c            |  2 +
 arch/x86/kernel/process-io.h          | 71 +++++++++++++++++++++++++++++++++++
 arch/x86/kernel/process.c             | 34 ++---------------
 arch/x86/kernel/process_32.c          | 11 +-----
 arch/x86/kernel/ptrace.c              |  8 ++++
 arch/x86/xen/enlighten.c              |  4 ++
 drivers/tty/vt/vt_ioctl.c             |  2 +-
 kernel/sys_ni.c                       |  5 +++
 16 files changed, 168 insertions(+), 61 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e241a19..d5b1e68 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -976,6 +976,16 @@ config VM86
 	  XFree86 to initialize some video cards via BIOS. Disabling this
 	  option saves about 6k.
 
+config X86_IOPORT
+	bool "iopl and ioperm system calls"
+	default y
+	---help---
+	  This option enables the iopl and ioperm system calls, which allow
+	  privileged userspace processes to directly access I/O ports. This
+	  is used by some legacy software to drive hardware directly from
+	  userspace rather than via a proper kernel driver. Unless you intend
+	  to run such software, you can safely say N here.
+
 config TOSHIBA
 	tristate "Toshiba Laptop support"
 	depends on X86_32
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 401f350..2e106d5 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -299,10 +299,12 @@ static inline void write_idt_entry(gate_desc *dt, int
entry, const gate_desc *g)
 {
 	PVOP_VCALL3(pv_cpu_ops.write_idt_entry, dt, entry, g);
 }
+#ifdef CONFIG_X86_IOPORT
 static inline void set_iopl_mask(unsigned mask)
 {
 	PVOP_VCALL1(pv_cpu_ops.set_iopl_mask, mask);
 }
+#endif /* CONFIG_X86_IOPORT */
 
 /* The paravirtualized I/O functions */
 static inline void slow_down_io(void)
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index aab8f67..bc5bfeb 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -142,7 +142,9 @@ struct pv_cpu_ops {
 
 	void (*load_sp0)(struct tss_struct *tss, struct thread_struct *t);
 
+#ifdef CONFIG_X86_IOPORT
 	void (*set_iopl_mask)(unsigned mask);
+#endif /* CONFIG_X86_IOPORT */
 
 	void (*wbinvd)(void);
 	void (*io_delay)(void);
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 03d3003..48f6fbe 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -256,7 +256,11 @@ struct x86_hw_tss {
 /*
  * IO-bitmap sizes:
  */
+#ifdef CONFIG_X86_IOPORT
 #define IO_BITMAP_BITS			65536
+#else
+#define IO_BITMAP_BITS			0
+#endif
 #define IO_BITMAP_BYTES			(IO_BITMAP_BITS/8)
 #define IO_BITMAP_LONGS			(IO_BITMAP_BYTES/sizeof(long))
 #define INVALID_IO_BITMAP_OFFSET	0x8000
@@ -269,6 +273,7 @@ struct tss_struct {
 	 */
 	struct x86_hw_tss	x86_tss;
 
+#ifdef CONFIG_X86_IOPORT
 	/*
 	 * The extra 1 is there because the CPU will access an
 	 * additional byte beyond the end of the IO permission
@@ -276,6 +281,7 @@ struct tss_struct {
 	 * be within the limit.
 	 */
 	unsigned long		io_bitmap[IO_BITMAP_LONGS + 1];
+#endif /* CONFIG_X86_IOPORT */
 
 	/*
 	 * .. and then another 0x100 bytes for the emergency kernel stack:
@@ -286,6 +292,24 @@ struct tss_struct {
 
 DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, init_tss);
 
+static inline void init_tss_io(struct tss_struct *t)
+{
+#ifdef CONFIG_X86_IOPORT
+	int i;
+
+	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
+
+	/*
+	 * <= is required because the CPU will access up to
+	 * 8 bits beyond the end of the IO permission bitmap.
+	 */
+	for (i = 0; i <= IO_BITMAP_LONGS; i++)
+		t->io_bitmap[i] = ~0UL;
+#else
+	t->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
+#endif
+}
+
 /*
  * Save the original ist values for checking stack pointers during debugging
  */
@@ -484,13 +508,16 @@ struct thread_struct {
 	unsigned int		saved_fs;
 	unsigned int		saved_gs;
 #endif
+#ifdef CONFIG_X86_IOPORT
 	/* IO permissions: */
 	unsigned long		*io_bitmap_ptr;
 	unsigned long		iopl;
 	/* Max allowed port in the bitmap, in bytes: */
 	unsigned		io_bitmap_max;
+#endif /* CONFIG_X86_IOPORT */
 };
 
+#ifdef CONFIG_X86_IOPORT
 /*
  * Set IOPL bits in EFLAGS from given mask
  */
@@ -509,6 +536,7 @@ static inline void native_set_iopl_mask(unsigned mask)
 		      : "i" (~X86_EFLAGS_IOPL), "r" (mask));
 #endif
 }
+#endif /* CONFIG_X86_IOPORT */
 
 static inline void
 native_load_sp0(struct tss_struct *tss, struct thread_struct *thread)
@@ -828,12 +856,8 @@ static inline void spin_lock_prefetch(const void *x)
 #define STACK_TOP		TASK_SIZE
 #define STACK_TOP_MAX		STACK_TOP
 
-#define INIT_THREAD  {							  \
-	.sp0			= sizeof(init_stack) + (long)&init_stack, \
-	.vm86_info		= NULL,					  \
-	.sysenter_cs		= __KERNEL_CS,				  \
-	.io_bitmap_ptr		= NULL,					  \
-}
+#ifdef CONFIG_X86_IOPORT
+#define INIT_THREAD_IO .io_bitmap_ptr = NULL,
 
 /*
  * Note that the .io_bitmap member must be extra-big. This is because
@@ -841,6 +865,19 @@ static inline void spin_lock_prefetch(const void *x)
  * permission bitmap. The extra byte must be all 1 bits, and must
  * be within the limit.
  */
+#define INIT_TSS_IO .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
+#else
+#define INIT_THREAD_IO
+#define INIT_TSS_IO
+#endif
+
+#define INIT_THREAD  {							  \
+	.sp0			= sizeof(init_stack) + (long)&init_stack, \
+	.vm86_info		= NULL,					  \
+	.sysenter_cs		= __KERNEL_CS,				  \
+	INIT_THREAD_IO							  \
+}
+
 #define INIT_TSS  {							  \
 	.x86_tss = {							  \
 		.sp0		= sizeof(init_stack) + (long)&init_stack, \
@@ -848,7 +885,7 @@ static inline void spin_lock_prefetch(const void *x)
 		.ss1		= __KERNEL_CS,				  \
 		.io_bitmap_base	= INVALID_IO_BITMAP_OFFSET,		  \
 	 },								  \
-	.io_bitmap		= { [0 ... IO_BITMAP_LONGS] = ~0 },	  \
+	INIT_TSS_IO							  \
 }
 
 extern unsigned long thread_saved_pc(struct task_struct *tsk);
diff --git a/arch/x86/include/asm/syscalls.h b/arch/x86/include/asm/syscalls.h
index 592a6a6..4db79ea 100644
--- a/arch/x86/include/asm/syscalls.h
+++ b/arch/x86/include/asm/syscalls.h
@@ -16,9 +16,12 @@
 #include <linux/types.h>
 
 /* Common in X86_32 and X86_64 */
+
+#ifdef CONFIG_X86_IOPORT
 /* kernel/ioport.c */
 asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
 asmlinkage long sys_iopl(unsigned int);
+#endif /* CONFIG_X86_IOPORT */
 
 /* kernel/ldt.c */
 asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index a5408b9..9644737 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -20,7 +20,8 @@ CFLAGS_irq.o := -I$(src)/../include/asm/trace
 
 obj-y			:= process_$(BITS).o signal.o entry_$(BITS).o
 obj-y			+= traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
-obj-y			+= time.o ioport.o ldt.o dumpstack.o nmi.o
+obj-y			+= time.o ldt.o dumpstack.o nmi.o
+obj-$(CONFIG_X86_IOPORT) += ioport.o
 obj-y			+= setup.o x86_init.o i8259.o irqinit.o jump_label.o
 obj-$(CONFIG_IRQ_WORK)  += irq_work.o
 obj-y			+= probe_roms.o
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 2793d1f..01235ef 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1223,7 +1223,6 @@ void cpu_init(void)
 	struct tss_struct *t;
 	unsigned long v;
 	int cpu;
-	int i;
 
 	/*
 	 * Load microcode on this cpu if a valid microcode is available.
@@ -1285,14 +1284,7 @@ void cpu_init(void)
 		}
 	}
 
-	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
-
-	/*
-	 * <= is required because the CPU will access up to
-	 * 8 bits beyond the end of the IO permission bitmap.
-	 */
-	for (i = 0; i <= IO_BITMAP_LONGS; i++)
-		t->io_bitmap[i] = ~0UL;
+	init_tss_io(t);
 
 	atomic_inc(&init_mm.mm_count);
 	me->active_mm = &init_mm;
@@ -1351,7 +1343,7 @@ void cpu_init(void)
 	load_TR_desc();
 	load_LDT(&init_mm.context);
 
-	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
+	init_tss_io(t);
 
 #ifdef CONFIG_DOUBLEFAULT
 	/* Set up doublefault TSS pointer in the GDT */
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1b69951..eb4f5ba 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -844,6 +844,11 @@ ENTRY(stub_\func)
 END(stub_\func)
 	.endm
 
+	FORK_LIKE  clone
+	FORK_LIKE  fork
+	FORK_LIKE  vfork
+
+#ifdef CONFIG_X86_IOPORT
 	.macro FIXED_FRAME label,func
 ENTRY(\label)
 	CFI_STARTPROC
@@ -856,10 +861,8 @@ ENTRY(\label)
 END(\label)
 	.endm
 
-	FORK_LIKE  clone
-	FORK_LIKE  fork
-	FORK_LIKE  vfork
 	FIXED_FRAME stub_iopl, sys_iopl
+#endif /* CONFIG_X86_IOPORT */
 
 ENTRY(ptregscall_common)
 	DEFAULT_FRAME 1 8	/* offset 8: return address */
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 1b10af8..46da3d9 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -382,7 +382,9 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.iret = native_iret,
 	.swapgs = native_swapgs,
 
+#ifdef CONFIG_X86_IOPORT
 	.set_iopl_mask = native_set_iopl_mask,
+#endif /* CONFIG_X86_IOPORT */
 	.io_delay = native_io_delay,
 
 	.start_context_switch = paravirt_nop,
diff --git a/arch/x86/kernel/process-io.h b/arch/x86/kernel/process-io.h
index d884444..3e773fa 100644
--- a/arch/x86/kernel/process-io.h
+++ b/arch/x86/kernel/process-io.h
@@ -1,9 +1,17 @@
 #ifndef _X86_KERNEL_PROCESS_IO_H
 #define _X86_KERNEL_PROCESS_IO_H
 
+static inline void clear_thread_io_bitmap(struct task_struct *p)
+{
+#ifdef CONFIG_X86_IOPORT
+	p->thread.io_bitmap_ptr = NULL;
+#endif /* CONFIG_X86_IOPORT */
+}
+
 static inline int copy_io_bitmap(struct task_struct *me,
 				 struct task_struct *p)
 {
+#ifdef CONFIG_X86_IOPORT
 	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
 		p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
 						  IO_BITMAP_BYTES, GFP_KERNEL);
@@ -15,8 +23,71 @@ static inline int copy_io_bitmap(struct task_struct *me,
 	} else {
 		p->thread.io_bitmap_ptr = NULL;
 	}
+#endif /* CONFIG_X86_IOPORT */
 
 	return 0;
 }
 
+static inline void exit_thread_io(struct task_struct *me)
+{
+#ifdef CONFIG_X86_IOPORT
+        struct thread_struct *t = &me->thread;
+        unsigned long *bp = t->io_bitmap_ptr;
+
+        if (bp) {
+                struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
+
+                t->io_bitmap_ptr = NULL;
+                clear_thread_flag(TIF_IO_BITMAP);
+                /*
+                 * Careful, clear this in the TSS too:
+                 */
+                memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
+                t->io_bitmap_max = 0;
+                put_cpu();
+                kfree(bp);
+        }
+#endif /* CONFIG_X86_IOPORT */
+}
+
+static inline void switch_iopl_mask(struct thread_struct *prev,
+				    struct thread_struct *next)
+{
+#ifdef CONFIG_X86_IOPORT
+        /*
+         * Restore IOPL if needed.  In normal use, the flags restore
+         * in the switch assembly will handle this.  But if the kernel
+         * is running virtualized at a non-zero CPL, the popf will
+         * not restore flags, so it must be done in a separate step.
+         */
+        if (get_kernel_rpl() && unlikely(prev->iopl !=
next->iopl))
+                set_iopl_mask(next->iopl);
+#endif /* CONFIG_X86_IOPORT */
+}
+
+static inline void switch_io_bitmap(struct tss_struct *tss,
+				    struct task_struct *prev_p,
+				    struct task_struct *next_p)
+{
+#ifdef CONFIG_X86_IOPORT
+        struct thread_struct *prev, *next;
+        prev = &prev_p->thread;
+        next = &next_p->thread;
+
+        if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
+                /*
+                 * Copy the relevant range of the IO bitmap.
+                 * Normally this is 128 bytes or less:
+                 */
+                memcpy(tss->io_bitmap, next->io_bitmap_ptr,
+                       max(prev->io_bitmap_max, next->io_bitmap_max));
+        } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
+                /*
+                 * Clear any possible leftover bits:
+                 */
+                memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
+        }
+#endif /* CONFIG_X86_IOPORT */
+}
+
 #endif /* _X86_KERNEL_PROCESS_IO_H */
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c83516b..2df5b00 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -29,6 +29,8 @@
 #include <asm/debugreg.h>
 #include <asm/nmi.h>
 
+#include "process-io.h"
+
 /*
  * per-CPU TSS segments. Threads are completely 'soft' on Linux,
  * no more per-task TSS's. The TSS size is kept cacheline-aligned
@@ -101,23 +103,7 @@ void arch_task_cache_init(void)
 void exit_thread(void)
 {
 	struct task_struct *me = current;
-	struct thread_struct *t = &me->thread;
-	unsigned long *bp = t->io_bitmap_ptr;
-
-	if (bp) {
-		struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
-
-		t->io_bitmap_ptr = NULL;
-		clear_thread_flag(TIF_IO_BITMAP);
-		/*
-		 * Careful, clear this in the TSS too:
-		 */
-		memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
-		t->io_bitmap_max = 0;
-		put_cpu();
-		kfree(bp);
-	}
-
+	exit_thread_io(me);
 	drop_fpu(me);
 }
 
@@ -222,19 +208,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct
task_struct *next_p,
 			hard_enable_TSC();
 	}
 
-	if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
-		/*
-		 * Copy the relevant range of the IO bitmap.
-		 * Normally this is 128 bytes or less:
-		 */
-		memcpy(tss->io_bitmap, next->io_bitmap_ptr,
-		       max(prev->io_bitmap_max, next->io_bitmap_max));
-	} else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
-		/*
-		 * Clear any possible leftover bits:
-		 */
-		memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
-	}
+	switch_io_bitmap(tss, prev_p, next_p);
 	propagate_user_return_notify(prev_p, next_p);
 }
 
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index e86028b..dc780cb 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -155,7 +155,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 		childregs->cs = __KERNEL_CS | get_kernel_rpl();
 		childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
 		p->fpu_counter = 0;
-		p->thread.io_bitmap_ptr = NULL;
+		clear_thread_io_bitmap(p);
 		memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 		return 0;
 	}
@@ -269,14 +269,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct
*next_p)
 	 */
 	load_TLS(next, cpu);
 
-	/*
-	 * Restore IOPL if needed.  In normal use, the flags restore
-	 * in the switch assembly will handle this.  But if the kernel
-	 * is running virtualized at a non-zero CPL, the popf will
-	 * not restore flags, so it must be done in a separate step.
-	 */
-	if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
-		set_iopl_mask(next->iopl);
+	switch_iopl_mask(prev, next);
 
 	/*
 	 * Now maybe handle debug registers and/or IO bitmaps
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 7461f50..f071bfa 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -785,7 +785,11 @@ static int ptrace_set_debugreg(struct task_struct *tsk, int
n,
 static int ioperm_active(struct task_struct *target,
 			 const struct user_regset *regset)
 {
+#ifdef CONFIG_X86_IOPORT
 	return target->thread.io_bitmap_max / regset->size;
+#else
+	return 0;
+#endif
 }
 
 static int ioperm_get(struct task_struct *target,
@@ -793,12 +797,16 @@ static int ioperm_get(struct task_struct *target,
 		      unsigned int pos, unsigned int count,
 		      void *kbuf, void __user *ubuf)
 {
+#ifdef CONFIG_X86_IOPORT
 	if (!target->thread.io_bitmap_ptr)
 		return -ENXIO;
 
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 				   target->thread.io_bitmap_ptr,
 				   0, IO_BITMAP_BYTES);
+#else
+	return -ENXIO;
+#endif
 }
 
 /*
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index fa6ade7..f485d92 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -911,6 +911,7 @@ static void xen_load_sp0(struct tss_struct *tss,
 	xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
+#ifdef CONFIG_X86_IOPORT
 static void xen_set_iopl_mask(unsigned mask)
 {
 	struct physdev_set_iopl set_iopl;
@@ -919,6 +920,7 @@ static void xen_set_iopl_mask(unsigned mask)
 	set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
 	HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
 }
+#endif /* CONFIG_X86_IOPORT */
 
 static void xen_io_delay(void)
 {
@@ -1277,7 +1279,9 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
 	.write_idt_entry = xen_write_idt_entry,
 	.load_sp0 = xen_load_sp0,
 
+#ifdef CONFIG_X86_IOPORT
 	.set_iopl_mask = xen_set_iopl_mask,
+#endif /* CONFIG_X86_IOPORT */
 	.io_delay = xen_io_delay,
 
 	/* Xen takes care of %gs when switching to usermode for us */
diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
index 2bd78e2..7c7d405 100644
--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -410,7 +410,7 @@ int vt_ioctl(struct tty_struct *tty,
 		 *
 		 * XXX: you should never use these, just call ioperm directly..
 		 */
-#ifdef CONFIG_X86
+#ifdef CONFIG_X86_IOPORT
 	case KDADDIO:
 	case KDDELIO:
 		/*
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 7078052..e7f4a35 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -209,3 +209,8 @@ cond_syscall(compat_sys_open_by_handle_at);
 
 /* compare kernel pointers */
 cond_syscall(sys_kcmp);
+
+/* userspace I/O port access */
+cond_syscall(stub_iopl);
+cond_syscall(sys_iopl);
+cond_syscall(sys_ioperm);
-- 
1.8.4.rc3

I/O from userspace  is used to implement usermode virtio driver(s).
This has been done independently by Intel, Brocade/Vyatta, and 6Wind.
Sorry, it has to stay.


On Mon, Oct 21, 2013 at 7:35 PM, Josh Triplett <josh at joshtriplett.org>
wrote:
> On the vast majority of modern systems, no processes will use the
> userspsace I/O syscalls, iopl and ioperm.  Add a new config option,
> CONFIG_X86_IOPORT, to support configuring them out of the kernel
> entirely.  Since these syscalls only exist to support rare legacy
> userspace programs, X86_IOPORT does not depend on EXPERT, though it does
> still default to y.
>
> In addition to saving a significant amount of space, this also reduces
> the size of several major kernel data structures, drops a bit of code
> from several task-related hot paths, and reduces the attack surface of
> the kernel.
>
> All of the task-related code dealing with userspace I/O permissions now
> lives in process-io.h as several new inline functions, which become
> no-ops when CONFIG_X86_IOPORT.
>
> bloat-o-meter shows a net reduction of 17681 bytes on 32-bit and 9719
> bytes on 64-bit:
>
> 32-bit bloat-o-meter:
> add/remove: 0/3 grow/shrink: 0/10 up/down: 0/-17681 (-17681)
> function                                     old     new   delta
> cpu_init                                     676     668      -8
> ioperm_active                                 18       7     -11
> init_task                                   1296    1284     -12
> exit_thread                                  179      91     -88
> ioperm_get                                   103      10     -93
> __switch_to_xtra                             254     161     -93
> sys_iopl                                     127       -    -127
> SyS_iopl                                     127       -    -127
> copy_thread                                  606     446    -160
> vt_ioctl                                    4127    3919    -208
> sys_ioperm                                   370       -    -370
> init_tss                                    8576     384   -8192
> doublefault_tss                             8576     384   -8192
>
> 64-bit bloat-o-meter:
> add/remove: 0/4 grow/shrink: 2/9 up/down: 45/-9764 (-9719)
> function                                     old     new   delta
> cpu_init                                     958     995     +37
> arch_align_stack                              78      86      +8
> perf_event_exit_task                         525     517      -8
> ioperm_active                                 17       8      -9
> init_task                                   1968    1944     -24
> stub_iopl                                     81       -     -81
> ioperm_get                                   111      11    -100
> __switch_to_xtra                             281     164    -117
> exit_thread                                  212      92    -120
> vt_ioctl                                    4432    4304    -128
> sys_iopl                                     137       -    -137
> SyS_iopl                                     137       -    -137
> copy_thread                                  694     520    -174
> sys_ioperm                                   473       -    -473
> init_tss                                    8896     640   -8256
>
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
> ---
>  arch/x86/Kconfig                      | 10 +++++
>  arch/x86/include/asm/paravirt.h       |  2 +
>  arch/x86/include/asm/paravirt_types.h |  2 +
>  arch/x86/include/asm/processor.h      | 51 +++++++++++++++++++++----
>  arch/x86/include/asm/syscalls.h       |  3 ++
>  arch/x86/kernel/Makefile              |  3 +-
>  arch/x86/kernel/cpu/common.c          | 12 +-----
>  arch/x86/kernel/entry_64.S            |  9 +++--
>  arch/x86/kernel/paravirt.c            |  2 +
>  arch/x86/kernel/process-io.h          | 71
+++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/process.c             | 34 ++---------------
>  arch/x86/kernel/process_32.c          | 11 +-----
>  arch/x86/kernel/ptrace.c              |  8 ++++
>  arch/x86/xen/enlighten.c              |  4 ++
>  drivers/tty/vt/vt_ioctl.c             |  2 +-
>  kernel/sys_ni.c                       |  5 +++
>  16 files changed, 168 insertions(+), 61 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index e241a19..d5b1e68 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -976,6 +976,16 @@ config VM86
>           XFree86 to initialize some video cards via BIOS. Disabling this
>           option saves about 6k.
>
> +config X86_IOPORT
> +       bool "iopl and ioperm system calls"
> +       default y
> +       ---help---
> +         This option enables the iopl and ioperm system calls, which allow
> +         privileged userspace processes to directly access I/O ports. This
> +         is used by some legacy software to drive hardware directly from
> +         userspace rather than via a proper kernel driver. Unless you
intend
> +         to run such software, you can safely say N here.
> +
>  config TOSHIBA
>         tristate "Toshiba Laptop support"
>         depends on X86_32
> diff --git a/arch/x86/include/asm/paravirt.h
b/arch/x86/include/asm/paravirt.h
> index 401f350..2e106d5 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -299,10 +299,12 @@ static inline void write_idt_entry(gate_desc *dt, int
entry, const gate_desc *g)
>  {
>         PVOP_VCALL3(pv_cpu_ops.write_idt_entry, dt, entry, g);
>  }
> +#ifdef CONFIG_X86_IOPORT
>  static inline void set_iopl_mask(unsigned mask)
>  {
>         PVOP_VCALL1(pv_cpu_ops.set_iopl_mask, mask);
>  }
> +#endif /* CONFIG_X86_IOPORT */
>
>  /* The paravirtualized I/O functions */
>  static inline void slow_down_io(void)
> diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
> index aab8f67..bc5bfeb 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -142,7 +142,9 @@ struct pv_cpu_ops {
>
>         void (*load_sp0)(struct tss_struct *tss, struct thread_struct *t);
>
> +#ifdef CONFIG_X86_IOPORT
>         void (*set_iopl_mask)(unsigned mask);
> +#endif /* CONFIG_X86_IOPORT */
>
>         void (*wbinvd)(void);
>         void (*io_delay)(void);
> diff --git a/arch/x86/include/asm/processor.h
b/arch/x86/include/asm/processor.h
> index 03d3003..48f6fbe 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -256,7 +256,11 @@ struct x86_hw_tss {
>  /*
>   * IO-bitmap sizes:
>   */
> +#ifdef CONFIG_X86_IOPORT
>  #define IO_BITMAP_BITS                 65536
> +#else
> +#define IO_BITMAP_BITS                 0
> +#endif
>  #define IO_BITMAP_BYTES                        (IO_BITMAP_BITS/8)
>  #define IO_BITMAP_LONGS                       
(IO_BITMAP_BYTES/sizeof(long))
>  #define INVALID_IO_BITMAP_OFFSET       0x8000
> @@ -269,6 +273,7 @@ struct tss_struct {
>          */
>         struct x86_hw_tss       x86_tss;
>
> +#ifdef CONFIG_X86_IOPORT
>         /*
>          * The extra 1 is there because the CPU will access an
>          * additional byte beyond the end of the IO permission
> @@ -276,6 +281,7 @@ struct tss_struct {
>          * be within the limit.
>          */
>         unsigned long           io_bitmap[IO_BITMAP_LONGS + 1];
> +#endif /* CONFIG_X86_IOPORT */
>
>         /*
>          * .. and then another 0x100 bytes for the emergency kernel stack:
> @@ -286,6 +292,24 @@ struct tss_struct {
>
>  DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, init_tss);
>
> +static inline void init_tss_io(struct tss_struct *t)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +       int i;
> +
> +       t->x86_tss.io_bitmap_base = offsetof(struct tss_struct,
io_bitmap);
> +
> +       /*
> +        * <= is required because the CPU will access up to
> +        * 8 bits beyond the end of the IO permission bitmap.
> +        */
> +       for (i = 0; i <= IO_BITMAP_LONGS; i++)
> +               t->io_bitmap[i] = ~0UL;
> +#else
> +       t->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
> +#endif
> +}
> +
>  /*
>   * Save the original ist values for checking stack pointers during
debugging
>   */
> @@ -484,13 +508,16 @@ struct thread_struct {
>         unsigned int            saved_fs;
>         unsigned int            saved_gs;
>  #endif
> +#ifdef CONFIG_X86_IOPORT
>         /* IO permissions: */
>         unsigned long           *io_bitmap_ptr;
>         unsigned long           iopl;
>         /* Max allowed port in the bitmap, in bytes: */
>         unsigned                io_bitmap_max;
> +#endif /* CONFIG_X86_IOPORT */
>  };
>
> +#ifdef CONFIG_X86_IOPORT
>  /*
>   * Set IOPL bits in EFLAGS from given mask
>   */
> @@ -509,6 +536,7 @@ static inline void native_set_iopl_mask(unsigned mask)
>                       : "i" (~X86_EFLAGS_IOPL), "r"
(mask));
>  #endif
>  }
> +#endif /* CONFIG_X86_IOPORT */
>
>  static inline void
>  native_load_sp0(struct tss_struct *tss, struct thread_struct *thread)
> @@ -828,12 +856,8 @@ static inline void spin_lock_prefetch(const void *x)
>  #define STACK_TOP              TASK_SIZE
>  #define STACK_TOP_MAX          STACK_TOP
>
> -#define INIT_THREAD  {                                                   \
> -       .sp0                    = sizeof(init_stack) +
(long)&init_stack, \
> -       .vm86_info              = NULL,                                   \
> -       .sysenter_cs            = __KERNEL_CS,                            \
> -       .io_bitmap_ptr          = NULL,                                   \
> -}
> +#ifdef CONFIG_X86_IOPORT
> +#define INIT_THREAD_IO .io_bitmap_ptr = NULL,
>
>  /*
>   * Note that the .io_bitmap member must be extra-big. This is because
> @@ -841,6 +865,19 @@ static inline void spin_lock_prefetch(const void *x)
>   * permission bitmap. The extra byte must be all 1 bits, and must
>   * be within the limit.
>   */
> +#define INIT_TSS_IO .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
> +#else
> +#define INIT_THREAD_IO
> +#define INIT_TSS_IO
> +#endif
> +
> +#define INIT_THREAD  {                                                   \
> +       .sp0                    = sizeof(init_stack) +
(long)&init_stack, \
> +       .vm86_info              = NULL,                                   \
> +       .sysenter_cs            = __KERNEL_CS,                            \
> +       INIT_THREAD_IO                                                    \
> +}
> +
>  #define INIT_TSS  {                                                      \
>         .x86_tss = {                                                      \
>                 .sp0            = sizeof(init_stack) +
(long)&init_stack, \
> @@ -848,7 +885,7 @@ static inline void spin_lock_prefetch(const void *x)
>                 .ss1            = __KERNEL_CS,                            \
>                 .io_bitmap_base = INVALID_IO_BITMAP_OFFSET,               \
>          },                                                               \
> -       .io_bitmap              = { [0 ... IO_BITMAP_LONGS] = ~0 },       \
> +       INIT_TSS_IO                                                       \
>  }
>
>  extern unsigned long thread_saved_pc(struct task_struct *tsk);
> diff --git a/arch/x86/include/asm/syscalls.h
b/arch/x86/include/asm/syscalls.h
> index 592a6a6..4db79ea 100644
> --- a/arch/x86/include/asm/syscalls.h
> +++ b/arch/x86/include/asm/syscalls.h
> @@ -16,9 +16,12 @@
>  #include <linux/types.h>
>
>  /* Common in X86_32 and X86_64 */
> +
> +#ifdef CONFIG_X86_IOPORT
>  /* kernel/ioport.c */
>  asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
>  asmlinkage long sys_iopl(unsigned int);
> +#endif /* CONFIG_X86_IOPORT */
>
>  /* kernel/ldt.c */
>  asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index a5408b9..9644737 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -20,7 +20,8 @@ CFLAGS_irq.o := -I$(src)/../include/asm/trace
>
>  obj-y                  := process_$(BITS).o signal.o entry_$(BITS).o
>  obj-y                  += traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
> -obj-y                  += time.o ioport.o ldt.o dumpstack.o nmi.o
> +obj-y                  += time.o ldt.o dumpstack.o nmi.o
> +obj-$(CONFIG_X86_IOPORT) += ioport.o
>  obj-y                  += setup.o x86_init.o i8259.o irqinit.o
jump_label.o
>  obj-$(CONFIG_IRQ_WORK)  += irq_work.o
>  obj-y                  += probe_roms.o
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 2793d1f..01235ef 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1223,7 +1223,6 @@ void cpu_init(void)
>         struct tss_struct *t;
>         unsigned long v;
>         int cpu;
> -       int i;
>
>         /*
>          * Load microcode on this cpu if a valid microcode is available.
> @@ -1285,14 +1284,7 @@ void cpu_init(void)
>                 }
>         }
>
> -       t->x86_tss.io_bitmap_base = offsetof(struct tss_struct,
io_bitmap);
> -
> -       /*
> -        * <= is required because the CPU will access up to
> -        * 8 bits beyond the end of the IO permission bitmap.
> -        */
> -       for (i = 0; i <= IO_BITMAP_LONGS; i++)
> -               t->io_bitmap[i] = ~0UL;
> +       init_tss_io(t);
>
>         atomic_inc(&init_mm.mm_count);
>         me->active_mm = &init_mm;
> @@ -1351,7 +1343,7 @@ void cpu_init(void)
>         load_TR_desc();
>         load_LDT(&init_mm.context);
>
> -       t->x86_tss.io_bitmap_base = offsetof(struct tss_struct,
io_bitmap);
> +       init_tss_io(t);
>
>  #ifdef CONFIG_DOUBLEFAULT
>         /* Set up doublefault TSS pointer in the GDT */
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 1b69951..eb4f5ba 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -844,6 +844,11 @@ ENTRY(stub_\func)
>  END(stub_\func)
>         .endm
>
> +       FORK_LIKE  clone
> +       FORK_LIKE  fork
> +       FORK_LIKE  vfork
> +
> +#ifdef CONFIG_X86_IOPORT
>         .macro FIXED_FRAME label,func
>  ENTRY(\label)
>         CFI_STARTPROC
> @@ -856,10 +861,8 @@ ENTRY(\label)
>  END(\label)
>         .endm
>
> -       FORK_LIKE  clone
> -       FORK_LIKE  fork
> -       FORK_LIKE  vfork
>         FIXED_FRAME stub_iopl, sys_iopl
> +#endif /* CONFIG_X86_IOPORT */
>
>  ENTRY(ptregscall_common)
>         DEFAULT_FRAME 1 8       /* offset 8: return address */
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 1b10af8..46da3d9 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -382,7 +382,9 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
>         .iret = native_iret,
>         .swapgs = native_swapgs,
>
> +#ifdef CONFIG_X86_IOPORT
>         .set_iopl_mask = native_set_iopl_mask,
> +#endif /* CONFIG_X86_IOPORT */
>         .io_delay = native_io_delay,
>
>         .start_context_switch = paravirt_nop,
> diff --git a/arch/x86/kernel/process-io.h b/arch/x86/kernel/process-io.h
> index d884444..3e773fa 100644
> --- a/arch/x86/kernel/process-io.h
> +++ b/arch/x86/kernel/process-io.h
> @@ -1,9 +1,17 @@
>  #ifndef _X86_KERNEL_PROCESS_IO_H
>  #define _X86_KERNEL_PROCESS_IO_H
>
> +static inline void clear_thread_io_bitmap(struct task_struct *p)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +       p->thread.io_bitmap_ptr = NULL;
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
>  static inline int copy_io_bitmap(struct task_struct *me,
>                                  struct task_struct *p)
>  {
> +#ifdef CONFIG_X86_IOPORT
>         if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
>                 p->thread.io_bitmap_ptr =
kmemdup(me->thread.io_bitmap_ptr,
>                                                   IO_BITMAP_BYTES,
GFP_KERNEL);
> @@ -15,8 +23,71 @@ static inline int copy_io_bitmap(struct task_struct *me,
>         } else {
>                 p->thread.io_bitmap_ptr = NULL;
>         }
> +#endif /* CONFIG_X86_IOPORT */
>
>         return 0;
>  }
>
> +static inline void exit_thread_io(struct task_struct *me)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +        struct thread_struct *t = &me->thread;
> +        unsigned long *bp = t->io_bitmap_ptr;
> +
> +        if (bp) {
> +                struct tss_struct *tss = &per_cpu(init_tss,
get_cpu());
> +
> +                t->io_bitmap_ptr = NULL;
> +                clear_thread_flag(TIF_IO_BITMAP);
> +                /*
> +                 * Careful, clear this in the TSS too:
> +                 */
> +                memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
> +                t->io_bitmap_max = 0;
> +                put_cpu();
> +                kfree(bp);
> +        }
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> +static inline void switch_iopl_mask(struct thread_struct *prev,
> +                                   struct thread_struct *next)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +        /*
> +         * Restore IOPL if needed.  In normal use, the flags restore
> +         * in the switch assembly will handle this.  But if the kernel
> +         * is running virtualized at a non-zero CPL, the popf will
> +         * not restore flags, so it must be done in a separate step.
> +         */
> +        if (get_kernel_rpl() && unlikely(prev->iopl !=
next->iopl))
> +                set_iopl_mask(next->iopl);
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> +static inline void switch_io_bitmap(struct tss_struct *tss,
> +                                   struct task_struct *prev_p,
> +                                   struct task_struct *next_p)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +        struct thread_struct *prev, *next;
> +        prev = &prev_p->thread;
> +        next = &next_p->thread;
> +
> +        if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> +                /*
> +                 * Copy the relevant range of the IO bitmap.
> +                 * Normally this is 128 bytes or less:
> +                 */
> +                memcpy(tss->io_bitmap, next->io_bitmap_ptr,
> +                       max(prev->io_bitmap_max,
next->io_bitmap_max));
> +        } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
> +                /*
> +                 * Clear any possible leftover bits:
> +                 */
> +                memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
> +        }
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
>  #endif /* _X86_KERNEL_PROCESS_IO_H */
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index c83516b..2df5b00 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -29,6 +29,8 @@
>  #include <asm/debugreg.h>
>  #include <asm/nmi.h>
>
> +#include "process-io.h"
> +
>  /*
>   * per-CPU TSS segments. Threads are completely 'soft' on Linux,
>   * no more per-task TSS's. The TSS size is kept cacheline-aligned
> @@ -101,23 +103,7 @@ void arch_task_cache_init(void)
>  void exit_thread(void)
>  {
>         struct task_struct *me = current;
> -       struct thread_struct *t = &me->thread;
> -       unsigned long *bp = t->io_bitmap_ptr;
> -
> -       if (bp) {
> -               struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
> -
> -               t->io_bitmap_ptr = NULL;
> -               clear_thread_flag(TIF_IO_BITMAP);
> -               /*
> -                * Careful, clear this in the TSS too:
> -                */
> -               memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
> -               t->io_bitmap_max = 0;
> -               put_cpu();
> -               kfree(bp);
> -       }
> -
> +       exit_thread_io(me);
>         drop_fpu(me);
>  }
>
> @@ -222,19 +208,7 @@ void __switch_to_xtra(struct task_struct *prev_p,
struct task_struct *next_p,
>                         hard_enable_TSC();
>         }
>
> -       if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> -               /*
> -                * Copy the relevant range of the IO bitmap.
> -                * Normally this is 128 bytes or less:
> -                */
> -               memcpy(tss->io_bitmap, next->io_bitmap_ptr,
> -                      max(prev->io_bitmap_max,
next->io_bitmap_max));
> -       } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
> -               /*
> -                * Clear any possible leftover bits:
> -                */
> -               memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
> -       }
> +       switch_io_bitmap(tss, prev_p, next_p);
>         propagate_user_return_notify(prev_p, next_p);
>  }
>
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index e86028b..dc780cb 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -155,7 +155,7 @@ int copy_thread(unsigned long clone_flags, unsigned
long sp,
>                 childregs->cs = __KERNEL_CS | get_kernel_rpl();
>                 childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
>                 p->fpu_counter = 0;
> -               p->thread.io_bitmap_ptr = NULL;
> +               clear_thread_io_bitmap(p);
>                 memset(p->thread.ptrace_bps, 0,
sizeof(p->thread.ptrace_bps));
>                 return 0;
>         }
> @@ -269,14 +269,7 @@ __switch_to(struct task_struct *prev_p, struct
task_struct *next_p)
>          */
>         load_TLS(next, cpu);
>
> -       /*
> -        * Restore IOPL if needed.  In normal use, the flags restore
> -        * in the switch assembly will handle this.  But if the kernel
> -        * is running virtualized at a non-zero CPL, the popf will
> -        * not restore flags, so it must be done in a separate step.
> -        */
> -       if (get_kernel_rpl() && unlikely(prev->iopl !=
next->iopl))
> -               set_iopl_mask(next->iopl);
> +       switch_iopl_mask(prev, next);
>
>         /*
>          * Now maybe handle debug registers and/or IO bitmaps
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index 7461f50..f071bfa 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -785,7 +785,11 @@ static int ptrace_set_debugreg(struct task_struct
*tsk, int n,
>  static int ioperm_active(struct task_struct *target,
>                          const struct user_regset *regset)
>  {
> +#ifdef CONFIG_X86_IOPORT
>         return target->thread.io_bitmap_max / regset->size;
> +#else
> +       return 0;
> +#endif
>  }
>
>  static int ioperm_get(struct task_struct *target,
> @@ -793,12 +797,16 @@ static int ioperm_get(struct task_struct *target,
>                       unsigned int pos, unsigned int count,
>                       void *kbuf, void __user *ubuf)
>  {
> +#ifdef CONFIG_X86_IOPORT
>         if (!target->thread.io_bitmap_ptr)
>                 return -ENXIO;
>
>         return user_regset_copyout(&pos, &count, &kbuf,
&ubuf,
>                                    target->thread.io_bitmap_ptr,
>                                    0, IO_BITMAP_BYTES);
> +#else
> +       return -ENXIO;
> +#endif
>  }
>
>  /*
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index fa6ade7..f485d92 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -911,6 +911,7 @@ static void xen_load_sp0(struct tss_struct *tss,
>         xen_mc_issue(PARAVIRT_LAZY_CPU);
>  }
>
> +#ifdef CONFIG_X86_IOPORT
>  static void xen_set_iopl_mask(unsigned mask)
>  {
>         struct physdev_set_iopl set_iopl;
> @@ -919,6 +920,7 @@ static void xen_set_iopl_mask(unsigned mask)
>         set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
>         HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
>  }
> +#endif /* CONFIG_X86_IOPORT */
>
>  static void xen_io_delay(void)
>  {
> @@ -1277,7 +1279,9 @@ static const struct pv_cpu_ops xen_cpu_ops
__initconst = {
>         .write_idt_entry = xen_write_idt_entry,
>         .load_sp0 = xen_load_sp0,
>
> +#ifdef CONFIG_X86_IOPORT
>         .set_iopl_mask = xen_set_iopl_mask,
> +#endif /* CONFIG_X86_IOPORT */
>         .io_delay = xen_io_delay,
>
>         /* Xen takes care of %gs when switching to usermode for us */
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 2bd78e2..7c7d405 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -410,7 +410,7 @@ int vt_ioctl(struct tty_struct *tty,
>                  *
>                  * XXX: you should never use these, just call ioperm
directly..
>                  */
> -#ifdef CONFIG_X86
> +#ifdef CONFIG_X86_IOPORT
>         case KDADDIO:
>         case KDDELIO:
>                 /*
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 7078052..e7f4a35 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -209,3 +209,8 @@ cond_syscall(compat_sys_open_by_handle_at);
>
>  /* compare kernel pointers */
>  cond_syscall(sys_kcmp);
> +
> +/* userspace I/O port access */
> +cond_syscall(stub_iopl);
> +cond_syscall(sys_iopl);
> +cond_syscall(sys_ioperm);
> --
> 1.8.4.rc3
>
> _______________________________________________
> Virtualization mailing list
> Virtualization at lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization

On Mon, Oct 21, 2013 at 7:34 PM, Josh Triplett <josh at joshtriplett.org>
wrote:
> The 32-bit and 64-bit versions of copy_thread have functionally
> identical handling for copying the I/O bitmap, modulo differences in
> error handling.  Clean up the error paths in both by moving the copy of
> the I/O bitmap to the end, to eliminate the need to free it if
> subsequent copy steps fail; move the resulting identical code to a
> static inline in a common header.
>
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
This seems quite sensible to me.

Acked-by: Kees Cook <keescook at chromium.org>

-- 
Kees Cook
Chrome OS Security

On Mon, Oct 21, 2013 at 7:34 PM, Josh Triplett <josh at joshtriplett.org>
wrote:
> __set_tss_desc has a complex calculation of the TSS segment limit,
> duplicating the quirky details of the I/O bitmap array length, and
> requiring a complex comment to explain.  Replace that calculation with a
> simpler one based on the offsetof the "stack" field that follows
the
> array.
>
> That then removes the last use of IO_BITMAP_OFFSET, so delete it.
>
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
> ---
>  arch/x86/include/asm/desc.h      | 11 +----------
>  arch/x86/include/asm/processor.h |  3 ++-
>  2 files changed, 3 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
> index b90e5df..17ac92f 100644
> --- a/arch/x86/include/asm/desc.h
> +++ b/arch/x86/include/asm/desc.h
> @@ -177,16 +177,7 @@ static inline void __set_tss_desc(unsigned cpu,
unsigned int entry, void *addr)
>         struct desc_struct *d = get_cpu_gdt_table(cpu);
>         tss_desc tss;
>
> -       /*
> -        * sizeof(unsigned long) coming from an extra "long" at
the end
> -        * of the iobitmap. See tss_struct definition in processor.h
> -        *
> -        * -1? seg base+limit should be pointing to the address of the
> -        * last valid byte
I think it might be better to keep at least a minimal comment near the
TSS_LIMIT declaration, just to explain the "-1" part, which is not
entirely obvious from just reading the code.

-Kees
> -        */
> -       set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS,
> -                             IO_BITMAP_OFFSET + IO_BITMAP_BYTES +
> -                             sizeof(unsigned long) - 1);
> +       set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS,
TSS_LIMIT);
>         write_gdt_entry(d, entry, &tss, DESC_TSS);
>  }
>
> diff --git a/arch/x86/include/asm/processor.h
b/arch/x86/include/asm/processor.h
> index 987c75e..03d3003 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -259,9 +259,10 @@ struct x86_hw_tss {
>  #define IO_BITMAP_BITS                 65536
>  #define IO_BITMAP_BYTES                        (IO_BITMAP_BITS/8)
>  #define IO_BITMAP_LONGS                       
(IO_BITMAP_BYTES/sizeof(long))
> -#define IO_BITMAP_OFFSET               offsetof(struct tss_struct,
io_bitmap)
>  #define INVALID_IO_BITMAP_OFFSET       0x8000
>
> +#define TSS_LIMIT      (offsetof(struct tss_struct, stack) - 1)
> +
>  struct tss_struct {
>         /*
>          * The hardware state:
> --
> 1.8.4.rc3
>


-- 
Kees Cook
Chrome OS Security

Hi Josh,

Since you added me to the CC, I had a look... Comments inline

On Tue, Oct 22, 2013, at 3:34, Josh Triplett wrote:
> The 32-bit and 64-bit versions of copy_thread have functionally
> identical handling for copying the I/O bitmap, modulo differences in
> error handling.  Clean up the error paths in both by moving the copy of
> the I/O bitmap to the end, to eliminate the need to free it if
> subsequent copy steps fail; move the resulting identical code to a
> static inline in a common header.
> 
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
> ---
>  arch/x86/kernel/process-io.h | 22 ++++++++++++++++++++++
I don't particularly like this new file. It's also not in a proper
place.
>  arch/x86/kernel/process_32.c | 29 ++++++++---------------------
>  arch/x86/kernel/process_64.c | 26 +++++---------------------
Yay, this I like :). However, unification is best done in a separate step. First
make the two parts equal in one or two patches. Then, in a separate patch,
do the mechanical unification.
>  3 files changed, 35 insertions(+), 42 deletions(-)
>  create mode 100644 arch/x86/kernel/process-io.h
> 
> diff --git a/arch/x86/kernel/process-io.h b/arch/x86/kernel/process-io.h
> new file mode 100644
> index 0000000..d884444
> --- /dev/null
> +++ b/arch/x86/kernel/process-io.h
> @@ -0,0 +1,22 @@
> +#ifndef _X86_KERNEL_PROCESS_IO_H
> +#define _X86_KERNEL_PROCESS_IO_H
> +
> +static inline int copy_io_bitmap(struct task_struct *me,
> +				 struct task_struct *p)
> +{
> +	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
> +		p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
> +						  IO_BITMAP_BYTES, GFP_KERNEL);
> +		if (!p->thread.io_bitmap_ptr) {
> +			p->thread.io_bitmap_max = 0;
> +			return -ENOMEM;
> +		}
> +		set_tsk_thread_flag(p, TIF_IO_BITMAP);
> +	} else {
> +		p->thread.io_bitmap_ptr = NULL;
> +	}
> +
> +	return 0;
> +}
> +
I really don't like the .h-file like this. Could you try avoiding it? I
think
it's possible to unify the copy_thread function and in the end move it
to process.c instead. The arch-specific parts can be split out in static
functions guarded by CONFIG_X86_64 (cooking up good names is
the challenge here ;) ).

Hi Josh,

On Tue, Oct 22, 2013, at 3:34, Josh Triplett wrote:
> __set_tss_desc has a complex calculation of the TSS segment limit,
> duplicating the quirky details of the I/O bitmap array length, and
> requiring a complex comment to explain.  Replace that calculation with a
> simpler one based on the offsetof the "stack" field that follows
the
> array.
> 
> That then removes the last use of IO_BITMAP_OFFSET, so delete it.
> 
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
> ---
>  arch/x86/include/asm/desc.h      | 11 +----------
>  arch/x86/include/asm/processor.h |  3 ++-
>  2 files changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
> index b90e5df..17ac92f 100644
> --- a/arch/x86/include/asm/desc.h
> +++ b/arch/x86/include/asm/desc.h
> @@ -177,16 +177,7 @@ static inline void __set_tss_desc(unsigned cpu,
unsigned int entry, void *addr)
>  	struct desc_struct *d = get_cpu_gdt_table(cpu);
>  	tss_desc tss;
>  
> -	/*
> -	 * sizeof(unsigned long) coming from an extra "long" at the end
> -	 * of the iobitmap. See tss_struct definition in processor.h
> -	 *
> -	 * -1? seg base+limit should be pointing to the address of the
> -	 * last valid byte
> -	 */
> -	set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS,
> -			      IO_BITMAP_OFFSET + IO_BITMAP_BYTES +
> -			      sizeof(unsigned long) - 1);
> +	set_tssldt_descriptor(&tss, (unsigned long)addr, DESC_TSS,
TSS_LIMIT);
>  	write_gdt_entry(d, entry, &tss, DESC_TSS);
>  }
>  
> diff --git a/arch/x86/include/asm/processor.h
b/arch/x86/include/asm/processor.h
> index 987c75e..03d3003 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -259,9 +259,10 @@ struct x86_hw_tss {
>  #define IO_BITMAP_BITS			65536
>  #define IO_BITMAP_BYTES			(IO_BITMAP_BITS/8)
>  #define IO_BITMAP_LONGS			(IO_BITMAP_BYTES/sizeof(long))
> -#define IO_BITMAP_OFFSET		offsetof(struct tss_struct, io_bitmap)
>  #define INVALID_IO_BITMAP_OFFSET	0x8000
>  
> +#define TSS_LIMIT	(offsetof(struct tss_struct, stack) - 1)
> +
I wonder if the 'stack' in tss_struct has any meaning anymore. Can it be
removed?
If so, the offsetof can be changed to sizeof(struct tss_struct), which looks
more
natural to me.

Even so, I think this is already an improvement.

Acked-by: Alexander van Heukelum <heukelum at fastmail.fm>
>  struct tss_struct {
>  	/*
>  	 * The hardware state:
> -- 
> 1.8.4.rc3
>

Hi Josh,

On Tue, Oct 22, 2013, at 3:35, Josh Triplett wrote:
> On the vast majority of modern systems, no processes will use the
> userspsace I/O syscalls, iopl and ioperm.  Add a new config option,
> CONFIG_X86_IOPORT, to support configuring them out of the kernel
> entirely.  Since these syscalls only exist to support rare legacy
> userspace programs, X86_IOPORT does not depend on EXPERT, though it does
> still default to y.
> 
> In addition to saving a significant amount of space, this also reduces
> the size of several major kernel data structures, drops a bit of code
> from several task-related hot paths, and reduces the attack surface of
> the kernel.
> 
> All of the task-related code dealing with userspace I/O permissions now
> lives in process-io.h as several new inline functions, which become
> no-ops when CONFIG_X86_IOPORT.
> 
> bloat-o-meter shows a net reduction of 17681 bytes on 32-bit and 9719
> bytes on 64-bit:
> 
> 32-bit bloat-o-meter:
> add/remove: 0/3 grow/shrink: 0/10 up/down: 0/-17681 (-17681)
> function                                     old     new   delta
> cpu_init                                     676     668      -8
> ioperm_active                                 18       7     -11
> init_task                                   1296    1284     -12
> exit_thread                                  179      91     -88
> ioperm_get                                   103      10     -93
> __switch_to_xtra                             254     161     -93
> sys_iopl                                     127       -    -127
> SyS_iopl                                     127       -    -127
These are not really different ;)
> copy_thread                                  606     446    -160
> vt_ioctl                                    4127    3919    -208
> sys_ioperm                                   370       -    -370
> init_tss                                    8576     384   -8192
> doublefault_tss                             8576     384   -8192
> 
> 64-bit bloat-o-meter:
> add/remove: 0/4 grow/shrink: 2/9 up/down: 45/-9764 (-9719)
> function                                     old     new   delta
> cpu_init                                     958     995     +37
> arch_align_stack                              78      86      +8
> perf_event_exit_task                         525     517      -8
> ioperm_active                                 17       8      -9
> init_task                                   1968    1944     -24
> stub_iopl                                     81       -     -81
> ioperm_get                                   111      11    -100
> __switch_to_xtra                             281     164    -117
> exit_thread                                  212      92    -120
> vt_ioctl                                    4432    4304    -128
> sys_iopl                                     137       -    -137
> SyS_iopl                                     137       -    -137
> copy_thread                                  694     520    -174
> sys_ioperm                                   473       -    -473
> init_tss                                    8896     640   -8256
> 
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
> ---
>  arch/x86/Kconfig                      | 10 +++++
>  arch/x86/include/asm/paravirt.h       |  2 +
>  arch/x86/include/asm/paravirt_types.h |  2 +
>  arch/x86/include/asm/processor.h      | 51 +++++++++++++++++++++----
>  arch/x86/include/asm/syscalls.h       |  3 ++
>  arch/x86/kernel/Makefile              |  3 +-
>  arch/x86/kernel/cpu/common.c          | 12 +-----
>  arch/x86/kernel/entry_64.S            |  9 +++--
>  arch/x86/kernel/paravirt.c            |  2 +
>  arch/x86/kernel/process-io.h          | 71
+++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/process.c             | 34 ++---------------
>  arch/x86/kernel/process_32.c          | 11 +-----
>  arch/x86/kernel/ptrace.c              |  8 ++++
>  arch/x86/xen/enlighten.c              |  4 ++
>  drivers/tty/vt/vt_ioctl.c             |  2 +-
>  kernel/sys_ni.c                       |  5 +++
>  16 files changed, 168 insertions(+), 61 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index e241a19..d5b1e68 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -976,6 +976,16 @@ config VM86
>  	  XFree86 to initialize some video cards via BIOS. Disabling this
>  	  option saves about 6k.
>  
> +config X86_IOPORT
> +	bool "iopl and ioperm system calls"
> +	default y
> +	---help---
> +	  This option enables the iopl and ioperm system calls, which allow
> +	  privileged userspace processes to directly access I/O ports. This
> +	  is used by some legacy software to drive hardware directly from
> +	  userspace rather than via a proper kernel driver. Unless you intend
> +	  to run such software, you can safely say N here.
> +
I think this entry should be under General setup / Configure standard kernel
features (expert users). Remove references to "legacy" and
"proper driver".
>  config TOSHIBA
>  	tristate "Toshiba Laptop support"
>  	depends on X86_32
> diff --git a/arch/x86/include/asm/paravirt.h
b/arch/x86/include/asm/paravirt.h
> index 401f350..2e106d5 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -299,10 +299,12 @@ static inline void write_idt_entry(gate_desc *dt, int
entry, const gate_desc *g)
>  {
>  	PVOP_VCALL3(pv_cpu_ops.write_idt_entry, dt, entry, g);
>  }
> +#ifdef CONFIG_X86_IOPORT
>  static inline void set_iopl_mask(unsigned mask)
>  {
>  	PVOP_VCALL1(pv_cpu_ops.set_iopl_mask, mask);
>  }
> +#endif /* CONFIG_X86_IOPORT */
>  
>  /* The paravirtualized I/O functions */
>  static inline void slow_down_io(void)
> diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
> index aab8f67..bc5bfeb 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -142,7 +142,9 @@ struct pv_cpu_ops {
>  
>  	void (*load_sp0)(struct tss_struct *tss, struct thread_struct *t);
>  
> +#ifdef CONFIG_X86_IOPORT
>  	void (*set_iopl_mask)(unsigned mask);
> +#endif /* CONFIG_X86_IOPORT */
>  
>  	void (*wbinvd)(void);
>  	void (*io_delay)(void);
> diff --git a/arch/x86/include/asm/processor.h
b/arch/x86/include/asm/processor.h
> index 03d3003..48f6fbe 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -256,7 +256,11 @@ struct x86_hw_tss {
>  /*
>   * IO-bitmap sizes:
>   */
> +#ifdef CONFIG_X86_IOPORT
>  #define IO_BITMAP_BITS			65536
> +#else
> +#define IO_BITMAP_BITS			0
> +#endif
>  #define IO_BITMAP_BYTES			(IO_BITMAP_BITS/8)
>  #define IO_BITMAP_LONGS			(IO_BITMAP_BYTES/sizeof(long))
>  #define INVALID_IO_BITMAP_OFFSET	0x8000
> @@ -269,6 +273,7 @@ struct tss_struct {
>  	 */
>  	struct x86_hw_tss	x86_tss;
>  
> +#ifdef CONFIG_X86_IOPORT
>  	/*
>  	 * The extra 1 is there because the CPU will access an
>  	 * additional byte beyond the end of the IO permission
> @@ -276,6 +281,7 @@ struct tss_struct {
>  	 * be within the limit.
>  	 */
>  	unsigned long		io_bitmap[IO_BITMAP_LONGS + 1];
> +#endif /* CONFIG_X86_IOPORT */
>  
>  	/*
>  	 * .. and then another 0x100 bytes for the emergency kernel stack:
> @@ -286,6 +292,24 @@ struct tss_struct {
>  
>  DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, init_tss);
>  
> +static inline void init_tss_io(struct tss_struct *t)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +	int i;
> +
> +	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
> +
> +	/*
> +	 * <= is required because the CPU will access up to
> +	 * 8 bits beyond the end of the IO permission bitmap.
> +	 */
> +	for (i = 0; i <= IO_BITMAP_LONGS; i++)
> +		t->io_bitmap[i] = ~0UL;
> +#else
> +	t->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
> +#endif
> +}
> +
>  /*
>   * Save the original ist values for checking stack pointers during
debugging
>   */
> @@ -484,13 +508,16 @@ struct thread_struct {
>  	unsigned int		saved_fs;
>  	unsigned int		saved_gs;
>  #endif
> +#ifdef CONFIG_X86_IOPORT
>  	/* IO permissions: */
>  	unsigned long		*io_bitmap_ptr;
>  	unsigned long		iopl;
>  	/* Max allowed port in the bitmap, in bytes: */
>  	unsigned		io_bitmap_max;
> +#endif /* CONFIG_X86_IOPORT */
>  };
>  
> +#ifdef CONFIG_X86_IOPORT
>  /*
>   * Set IOPL bits in EFLAGS from given mask
>   */
> @@ -509,6 +536,7 @@ static inline void native_set_iopl_mask(unsigned mask)
>  		      : "i" (~X86_EFLAGS_IOPL), "r" (mask));
>  #endif
>  }
> +#endif /* CONFIG_X86_IOPORT */
>  
>  static inline void
>  native_load_sp0(struct tss_struct *tss, struct thread_struct *thread)
> @@ -828,12 +856,8 @@ static inline void spin_lock_prefetch(const void *x)
>  #define STACK_TOP		TASK_SIZE
>  #define STACK_TOP_MAX		STACK_TOP
>  
> -#define INIT_THREAD  {							  \
> -	.sp0			= sizeof(init_stack) + (long)&init_stack, \
> -	.vm86_info		= NULL,					  \
> -	.sysenter_cs		= __KERNEL_CS,				  \
> -	.io_bitmap_ptr		= NULL,					  \
> -}
> +#ifdef CONFIG_X86_IOPORT
> +#define INIT_THREAD_IO .io_bitmap_ptr = NULL,
>  
>  /*
>   * Note that the .io_bitmap member must be extra-big. This is because
> @@ -841,6 +865,19 @@ static inline void spin_lock_prefetch(const void *x)
>   * permission bitmap. The extra byte must be all 1 bits, and must
>   * be within the limit.
>   */
> +#define INIT_TSS_IO .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
> +#else
> +#define INIT_THREAD_IO
> +#define INIT_TSS_IO
> +#endif
> +
> +#define INIT_THREAD  {							  \
> +	.sp0			= sizeof(init_stack) + (long)&init_stack, \
> +	.vm86_info		= NULL,					  \
> +	.sysenter_cs		= __KERNEL_CS,				  \
> +	INIT_THREAD_IO							  \
> +}
> +
>  #define INIT_TSS  {							  \
>  	.x86_tss = {							  \
>  		.sp0		= sizeof(init_stack) + (long)&init_stack, \
> @@ -848,7 +885,7 @@ static inline void spin_lock_prefetch(const void *x)
>  		.ss1		= __KERNEL_CS,				  \
>  		.io_bitmap_base	= INVALID_IO_BITMAP_OFFSET,		  \
>  	 },								  \
> -	.io_bitmap		= { [0 ... IO_BITMAP_LONGS] = ~0 },	  \
> +	INIT_TSS_IO							  \
>  }
>  
>  extern unsigned long thread_saved_pc(struct task_struct *tsk);
> diff --git a/arch/x86/include/asm/syscalls.h
b/arch/x86/include/asm/syscalls.h
> index 592a6a6..4db79ea 100644
> --- a/arch/x86/include/asm/syscalls.h
> +++ b/arch/x86/include/asm/syscalls.h
> @@ -16,9 +16,12 @@
>  #include <linux/types.h>
>  
>  /* Common in X86_32 and X86_64 */
> +
> +#ifdef CONFIG_X86_IOPORT
>  /* kernel/ioport.c */
>  asmlinkage long sys_ioperm(unsigned long, unsigned long, int);
>  asmlinkage long sys_iopl(unsigned int);
> +#endif /* CONFIG_X86_IOPORT */
>  
>  /* kernel/ldt.c */
>  asmlinkage int sys_modify_ldt(int, void __user *, unsigned long);
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index a5408b9..9644737 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -20,7 +20,8 @@ CFLAGS_irq.o := -I$(src)/../include/asm/trace
>  
>  obj-y			:= process_$(BITS).o signal.o entry_$(BITS).o
>  obj-y			+= traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
> -obj-y			+= time.o ioport.o ldt.o dumpstack.o nmi.o
> +obj-y			+= time.o ldt.o dumpstack.o nmi.o
> +obj-$(CONFIG_X86_IOPORT) += ioport.o
>  obj-y			+= setup.o x86_init.o i8259.o irqinit.o jump_label.o
>  obj-$(CONFIG_IRQ_WORK)  += irq_work.o
>  obj-y			+= probe_roms.o
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 2793d1f..01235ef 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1223,7 +1223,6 @@ void cpu_init(void)
>  	struct tss_struct *t;
>  	unsigned long v;
>  	int cpu;
> -	int i;
>  
>  	/*
>  	 * Load microcode on this cpu if a valid microcode is available.
> @@ -1285,14 +1284,7 @@ void cpu_init(void)
>  		}
>  	}
>  
> -	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
> -
> -	/*
> -	 * <= is required because the CPU will access up to
> -	 * 8 bits beyond the end of the IO permission bitmap.
> -	 */
> -	for (i = 0; i <= IO_BITMAP_LONGS; i++)
> -		t->io_bitmap[i] = ~0UL;
> +	init_tss_io(t);
>  
>  	atomic_inc(&init_mm.mm_count);
>  	me->active_mm = &init_mm;
> @@ -1351,7 +1343,7 @@ void cpu_init(void)
>  	load_TR_desc();
>  	load_LDT(&init_mm.context);
>  
> -	t->x86_tss.io_bitmap_base = offsetof(struct tss_struct, io_bitmap);
> +	init_tss_io(t);
This patch is too big. I think it would all look nicer if you added ioport.c in
one patch, and then convert the users in a separate patch?
>  #ifdef CONFIG_DOUBLEFAULT
>  	/* Set up doublefault TSS pointer in the GDT */
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 1b69951..eb4f5ba 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -844,6 +844,11 @@ ENTRY(stub_\func)
>  END(stub_\func)
>  	.endm
>  
> +	FORK_LIKE  clone
> +	FORK_LIKE  fork
> +	FORK_LIKE  vfork
> +
> +#ifdef CONFIG_X86_IOPORT
>  	.macro FIXED_FRAME label,func
>  ENTRY(\label)
>  	CFI_STARTPROC
> @@ -856,10 +861,8 @@ ENTRY(\label)
>  END(\label)
>  	.endm
>  
> -	FORK_LIKE  clone
> -	FORK_LIKE  fork
> -	FORK_LIKE  vfork
>  	FIXED_FRAME stub_iopl, sys_iopl
> +#endif /* CONFIG_X86_IOPORT */
>  
>  ENTRY(ptregscall_common)
>  	DEFAULT_FRAME 1 8	/* offset 8: return address */
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 1b10af8..46da3d9 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -382,7 +382,9 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
>  	.iret = native_iret,
>  	.swapgs = native_swapgs,
>  
> +#ifdef CONFIG_X86_IOPORT
>  	.set_iopl_mask = native_set_iopl_mask,
> +#endif /* CONFIG_X86_IOPORT */
>  	.io_delay = native_io_delay,
>  
>  	.start_context_switch = paravirt_nop,
> diff --git a/arch/x86/kernel/process-io.h b/arch/x86/kernel/process-io.h
> index d884444..3e773fa 100644
> --- a/arch/x86/kernel/process-io.h
> +++ b/arch/x86/kernel/process-io.h
> @@ -1,9 +1,17 @@
>  #ifndef _X86_KERNEL_PROCESS_IO_H
>  #define _X86_KERNEL_PROCESS_IO_H
>  
> +static inline void clear_thread_io_bitmap(struct task_struct *p)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +	p->thread.io_bitmap_ptr = NULL;
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
This is thought of as ugly... Instead, do something like

#ifndef CONFIG_X86_IOPORT

static inline void clear_thread_io_bitmap(struct task_struct *p) {}
static inline int copy_io_bitmap(struct task_struct *me, struct task_struct *p)
{return 0}
... etc...

#else

static inline void clear_thread_io_bitmap(struct task_struct *p)
{
   p->thread.io_bitmap_ptr = NULL;
}
... etc...

#endif

>  static inline int copy_io_bitmap(struct task_struct *me,
>  				 struct task_struct *p)
>  {
> +#ifdef CONFIG_X86_IOPORT
>  	if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
>  		p->thread.io_bitmap_ptr = kmemdup(me->thread.io_bitmap_ptr,
>  						  IO_BITMAP_BYTES, GFP_KERNEL);
> @@ -15,8 +23,71 @@ static inline int copy_io_bitmap(struct task_struct *me,
>  	} else {
>  		p->thread.io_bitmap_ptr = NULL;
>  	}
> +#endif /* CONFIG_X86_IOPORT */
>  
>  	return 0;
>  }
>  
> +static inline void exit_thread_io(struct task_struct *me)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +        struct thread_struct *t = &me->thread;
> +        unsigned long *bp = t->io_bitmap_ptr;
> +
> +        if (bp) {
> +                struct tss_struct *tss = &per_cpu(init_tss,
get_cpu());
> +
> +                t->io_bitmap_ptr = NULL;
> +                clear_thread_flag(TIF_IO_BITMAP);
> +                /*
> +                 * Careful, clear this in the TSS too:
> +                 */
> +                memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
> +                t->io_bitmap_max = 0;
> +                put_cpu();
> +                kfree(bp);
> +        }
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> +static inline void switch_iopl_mask(struct thread_struct *prev,
> +				    struct thread_struct *next)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +        /*
> +         * Restore IOPL if needed.  In normal use, the flags restore
> +         * in the switch assembly will handle this.  But if the kernel
> +         * is running virtualized at a non-zero CPL, the popf will
> +         * not restore flags, so it must be done in a separate step.
> +         */
> +        if (get_kernel_rpl() && unlikely(prev->iopl !=
next->iopl))
> +                set_iopl_mask(next->iopl);
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
> +static inline void switch_io_bitmap(struct tss_struct *tss,
> +				    struct task_struct *prev_p,
> +				    struct task_struct *next_p)
> +{
> +#ifdef CONFIG_X86_IOPORT
> +        struct thread_struct *prev, *next;
> +        prev = &prev_p->thread;
> +        next = &next_p->thread;
> +
> +        if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> +                /*
> +                 * Copy the relevant range of the IO bitmap.
> +                 * Normally this is 128 bytes or less:
> +                 */
> +                memcpy(tss->io_bitmap, next->io_bitmap_ptr,
> +                       max(prev->io_bitmap_max,
next->io_bitmap_max));
> +        } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
> +                /*
> +                 * Clear any possible leftover bits:
> +                 */
> +                memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
> +        }
> +#endif /* CONFIG_X86_IOPORT */
> +}
> +
>  #endif /* _X86_KERNEL_PROCESS_IO_H */
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index c83516b..2df5b00 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -29,6 +29,8 @@
>  #include <asm/debugreg.h>
>  #include <asm/nmi.h>
>  
> +#include "process-io.h"
> +
>  /*
>   * per-CPU TSS segments. Threads are completely 'soft' on Linux,
>   * no more per-task TSS's. The TSS size is kept cacheline-aligned
> @@ -101,23 +103,7 @@ void arch_task_cache_init(void)
>  void exit_thread(void)
>  {
>  	struct task_struct *me = current;
> -	struct thread_struct *t = &me->thread;
> -	unsigned long *bp = t->io_bitmap_ptr;
> -
> -	if (bp) {
> -		struct tss_struct *tss = &per_cpu(init_tss, get_cpu());
> -
> -		t->io_bitmap_ptr = NULL;
> -		clear_thread_flag(TIF_IO_BITMAP);
> -		/*
> -		 * Careful, clear this in the TSS too:
> -		 */
> -		memset(tss->io_bitmap, 0xff, t->io_bitmap_max);
> -		t->io_bitmap_max = 0;
> -		put_cpu();
> -		kfree(bp);
> -	}
> -
> +	exit_thread_io(me);
>  	drop_fpu(me);
>  }
>  
> @@ -222,19 +208,7 @@ void __switch_to_xtra(struct task_struct *prev_p,
struct task_struct *next_p,
>  			hard_enable_TSC();
>  	}
>  
> -	if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
> -		/*
> -		 * Copy the relevant range of the IO bitmap.
> -		 * Normally this is 128 bytes or less:
> -		 */
> -		memcpy(tss->io_bitmap, next->io_bitmap_ptr,
> -		       max(prev->io_bitmap_max, next->io_bitmap_max));
> -	} else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
> -		/*
> -		 * Clear any possible leftover bits:
> -		 */
> -		memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
> -	}
> +	switch_io_bitmap(tss, prev_p, next_p);
>  	propagate_user_return_notify(prev_p, next_p);
>  }
>  
> diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
> index e86028b..dc780cb 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -155,7 +155,7 @@ int copy_thread(unsigned long clone_flags, unsigned
long sp,
>  		childregs->cs = __KERNEL_CS | get_kernel_rpl();
>  		childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
>  		p->fpu_counter = 0;
> -		p->thread.io_bitmap_ptr = NULL;
> +		clear_thread_io_bitmap(p);
>  		memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
>  		return 0;
>  	}
> @@ -269,14 +269,7 @@ __switch_to(struct task_struct *prev_p, struct
task_struct *next_p)
>  	 */
>  	load_TLS(next, cpu);
>  
> -	/*
> -	 * Restore IOPL if needed.  In normal use, the flags restore
> -	 * in the switch assembly will handle this.  But if the kernel
> -	 * is running virtualized at a non-zero CPL, the popf will
> -	 * not restore flags, so it must be done in a separate step.
> -	 */
> -	if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
> -		set_iopl_mask(next->iopl);
> +	switch_iopl_mask(prev, next);
>  
>  	/*
>  	 * Now maybe handle debug registers and/or IO bitmaps
If copy_thread would be in process.c instead, the .h-file would be unnecessary,
right?
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index 7461f50..f071bfa 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -785,7 +785,11 @@ static int ptrace_set_debugreg(struct task_struct
*tsk, int n,
>  static int ioperm_active(struct task_struct *target,
>  			 const struct user_regset *regset)
>  {
> +#ifdef CONFIG_X86_IOPORT
>  	return target->thread.io_bitmap_max / regset->size;
> +#else
> +	return 0;
> +#endif
>  }
>  
>  static int ioperm_get(struct task_struct *target,
> @@ -793,12 +797,16 @@ static int ioperm_get(struct task_struct *target,
>  		      unsigned int pos, unsigned int count,
>  		      void *kbuf, void __user *ubuf)
>  {
> +#ifdef CONFIG_X86_IOPORT
>  	if (!target->thread.io_bitmap_ptr)
>  		return -ENXIO;
>  
>  	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
>  				   target->thread.io_bitmap_ptr,
>  				   0, IO_BITMAP_BYTES);
> +#else
> +	return -ENXIO;
> +#endif
>  }
>  
>  /*
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index fa6ade7..f485d92 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -911,6 +911,7 @@ static void xen_load_sp0(struct tss_struct *tss,
>  	xen_mc_issue(PARAVIRT_LAZY_CPU);
>  }
>  
> +#ifdef CONFIG_X86_IOPORT
>  static void xen_set_iopl_mask(unsigned mask)
>  {
>  	struct physdev_set_iopl set_iopl;
> @@ -919,6 +920,7 @@ static void xen_set_iopl_mask(unsigned mask)
>  	set_iopl.iopl = (mask == 0) ? 1 : (mask >> 12) & 3;
>  	HYPERVISOR_physdev_op(PHYSDEVOP_set_iopl, &set_iopl);
>  }
> +#endif /* CONFIG_X86_IOPORT */
>  
>  static void xen_io_delay(void)
>  {
> @@ -1277,7 +1279,9 @@ static const struct pv_cpu_ops xen_cpu_ops
__initconst = {
>  	.write_idt_entry = xen_write_idt_entry,
>  	.load_sp0 = xen_load_sp0,
>  
> +#ifdef CONFIG_X86_IOPORT
>  	.set_iopl_mask = xen_set_iopl_mask,
> +#endif /* CONFIG_X86_IOPORT */
>  	.io_delay = xen_io_delay,
>  
>  	/* Xen takes care of %gs when switching to usermode for us */
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 2bd78e2..7c7d405 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -410,7 +410,7 @@ int vt_ioctl(struct tty_struct *tty,
>  		 *
>  		 * XXX: you should never use these, just call ioperm directly..
>  		 */
> -#ifdef CONFIG_X86
> +#ifdef CONFIG_X86_IOPORT
>  	case KDADDIO:
>  	case KDDELIO:
>  		/*
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 7078052..e7f4a35 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -209,3 +209,8 @@ cond_syscall(compat_sys_open_by_handle_at);
>  
>  /* compare kernel pointers */
>  cond_syscall(sys_kcmp);
> +
> +/* userspace I/O port access */
> +cond_syscall(stub_iopl);
> +cond_syscall(sys_iopl);
> +cond_syscall(sys_ioperm);
> -- 
> 1.8.4.rc3
>