Linux Virtualization - Oct 2014 - [PATCH v3 1/3] x86: process: Unify 32-bit and 64-bit copy_thread I/O bitmap handling

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>
Acked-by: Kees Cook <keescook at chromium.org>
---
v3: No changes in this patch, only in patch 3/3.

 arch/x86/kernel/process-io.h | 22 ++++++++++++++++++++++
 arch/x86/kernel/process_32.c | 28 ++++++++--------------------
 arch/x86/kernel/process_64.c | 25 +++++--------------------
 3 files changed, 35 insertions(+), 40 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 8f3ebfe..07550ff 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -55,6 +55,8 @@
 #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");
 
@@ -134,7 +136,6 @@ 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);
@@ -166,32 +167,19 @@ int copy_thread(unsigned long clone_flags, unsigned long
sp,
 
 	p->thread.io_bitmap_ptr = NULL;
 	tsk = current;
-	err = -ENOMEM;
-
-	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 3ed4a68..b1babb4 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);
 
 __visible 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;
 
@@ -191,21 +192,11 @@ int copy_thread(unsigned long clone_flags, unsigned long
sp,
 	if (sp)
 		childregs->sp = sp;
 
-	err = -ENOMEM;
-	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,
@@ -214,16 +205,10 @@ 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
-- 
2.1.1

__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>
Acked-by: Alexander van Heukelum <heukelum at fastmail.fm>
---
v3: No changes in this patch, only in patch 3/3.

 arch/x86/include/asm/desc.h      | 11 +----------
 arch/x86/include/asm/processor.h |  4 +++-
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 50d033a..f8dc455 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 eb71ec7..76751cd 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -258,9 +258,11 @@ 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
 
+/* Segment limits point to the last valid byte, hence the -1 */
+#define TSS_LIMIT	(offsetof(struct tss_struct, stack) - 1)
+
 struct tss_struct {
 	/*
 	 * The hardware state:
-- 
2.1.1

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.  Most current systems do not run programs using these
syscalls, so 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 without CONFIG_X86_IOPORT.

bloat-o-meter results:

add/remove: 0/4 grow/shrink: 4/9 up/down: 83/-9074 (-8991)
function                                     old     new   delta
drop_fpu                                      80     160     +80
perf_event_init_task                         638     639      +1
perf_event_exec                              192     193      +1
perf_event_aux                               132     133      +1
test_tsk_thread_flag                          10       -     -10
ioperm_active                                 14       3     -11
init_task                                    916     904     -12
flush_thread                                 168     149     -19
cpu_init                                     364     339     -25
__drop_fpu                                    60       -     -60
ioperm_get                                    92       6     -86
exit_thread                                  105      10     -95
sys_iopl                                     106       -    -106
copy_thread                                  364     257    -107
__switch_to_xtra                             234     123    -111
sys_ioperm                                   240       -    -240
init_tss                                    8576     384   -8192

Signed-off-by: Josh Triplett <josh at joshtriplett.org>
---
v3: Eliminated several #ifdefs, and in particular almost all #ifdefs in
    .c files, by adding a macro INIT_SET_IOPL_MASK to use in place of
    the initializer for set_iopl_mask, and using __maybe_unused rather
    than wrapping function definitions in #ifdef.  Rebased on v3.18-rc1.
    Recomputed bloat-o-meter.

I assume this should go through the x86 tree rather than the tiny tree.

 arch/x86/Kconfig                      | 10 +++++
 arch/x86/include/asm/paravirt.h       |  2 +
 arch/x86/include/asm/paravirt_types.h |  5 +++
 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          | 13 ++-----
 arch/x86/kernel/process_64.c          |  2 +-
 arch/x86/kernel/ptrace.c              |  8 ++++
 arch/x86/xen/enlighten.c              |  4 +-
 drivers/tty/vt/vt_ioctl.c             |  2 +-
 kernel/sys_ni.c                       |  5 +++
 17 files changed, 169 insertions(+), 67 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f2327e8..a7de2eb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -984,6 +984,16 @@ config X86_ESPFIX64
 	def_bool y
 	depends on X86_16BIT && X86_64
 
+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 software that drives hardware directly from userspace
+	  without using a 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 cd6e161..52d2ec8 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 7549b8b..a22a5d4 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -142,7 +142,12 @@ 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);
+#define INIT_SET_IOPL_MASK(f) .set_iopl_mask = f,
+#else
+#define INIT_SET_IOPL_MASK(f)
+#endif
 
 	void (*wbinvd)(void);
 	void (*io_delay)(void);
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 76751cd..6e0b639 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -255,7 +255,11 @@ 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
  */
@@ -510,11 +534,13 @@ 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 */
 	/*
 	 * fpu_counter contains the number of consecutive context switches
 	 * that the FPU is used. If this is over a threshold, the lazy fpu
@@ -531,7 +557,7 @@ struct thread_struct {
  */
 static inline void native_set_iopl_mask(unsigned mask)
 {
-#ifdef CONFIG_X86_32
+#if defined(CONFIG_X86_IOPORT) && defined(CONFIG_X86_32)
 	unsigned int reg;
 
 	asm volatile ("pushfl;"
@@ -842,12 +868,8 @@ 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
@@ -855,6 +877,19 @@ 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, \
@@ -862,7 +897,7 @@ 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 8f1e774..84d5fbe 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 4b4f78c..ae2e8d7 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1297,7 +1297,6 @@ void cpu_init(void)
 	struct tss_struct *t;
 	unsigned long v;
 	int cpu = stack_smp_processor_id();
-	int i;
 
 	wait_for_master_cpu(cpu);
 
@@ -1357,14 +1356,7 @@ 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;
@@ -1419,7 +1411,7 @@ 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 df088bb..1e6a74e0 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -609,6 +609,11 @@ 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
@@ -621,10 +626,8 @@ 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 548d25f..e7969d4 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -383,7 +383,7 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.iret = native_iret,
 	.swapgs = native_swapgs,
 
-	.set_iopl_mask = native_set_iopl_mask,
+	INIT_SET_IOPL_MASK(native_set_iopl_mask)
 	.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 e127dda..7ac01bf 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
@@ -104,23 +106,7 @@ 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);
 }
 
@@ -225,19 +211,7 @@ 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 07550ff..3b82293 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -154,7 +154,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 		childregs->orig_ax = -1;
 		childregs->cs = __KERNEL_CS | get_kernel_rpl();
 		childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
-		p->thread.io_bitmap_ptr = NULL;
+		clear_thread_io_bitmap(p);
 		return 0;
 	}
 	*childregs = *current_pt_regs();
@@ -165,7 +165,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 	p->thread.ip = (unsigned long) ret_from_fork;
 	task_user_gs(p) = get_user_gs(current_pt_regs());
 
-	p->thread.io_bitmap_ptr = NULL;
+	clear_thread_io_bitmap(p);
 	tsk = current;
 
 	/*
@@ -265,14 +265,7 @@ __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);
 
 	/*
 	 * If it were not for PREEMPT_ACTIVE we could guarantee that the
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index b1babb4..d18f3fc 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -164,7 +164,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 	p->thread.sp = (unsigned long) childregs;
 	p->thread.usersp = me->thread.usersp;
 	set_tsk_thread_flag(p, TIF_FORK);
-	p->thread.io_bitmap_ptr = NULL;
+	clear_thread_io_bitmap(p);
 
 	savesegment(gs, p->thread.gsindex);
 	p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs;
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 749b0e4..fdb74a8 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 1a3f044..8ad0778 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -912,7 +912,7 @@ static void xen_load_sp0(struct tss_struct *tss,
 	xen_mc_issue(PARAVIRT_LAZY_CPU);
 }
 
-static void xen_set_iopl_mask(unsigned mask)
+static void __maybe_unused xen_set_iopl_mask(unsigned mask)
 {
 	struct physdev_set_iopl set_iopl;
 
@@ -1279,7 +1279,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
 	.write_idt_entry = xen_write_idt_entry,
 	.load_sp0 = xen_load_sp0,
 
-	.set_iopl_mask = xen_set_iopl_mask,
+	INIT_SET_IOPL_MASK(xen_set_iopl_mask)
 	.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 02aa418..f3014fe 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -224,3 +224,8 @@ cond_syscall(sys_seccomp);
 
 /* access BPF programs and maps */
 cond_syscall(sys_bpf);
+
+/* userspace I/O port access */
+cond_syscall(stub_iopl);
+cond_syscall(sys_iopl);
+cond_syscall(sys_ioperm);
-- 
2.1.1

On Wed, Oct 29, 2014 at 9:10 AM, 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.  Most current systems do not run programs using these
> syscalls, so 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 without CONFIG_X86_IOPORT.
>
> bloat-o-meter results:
>
> add/remove: 0/4 grow/shrink: 4/9 up/down: 83/-9074 (-8991)
> function                                     old     new   delta
> drop_fpu                                      80     160     +80
> perf_event_init_task                         638     639      +1
> perf_event_exec                              192     193      +1
> perf_event_aux                               132     133      +1
> test_tsk_thread_flag                          10       -     -10
> ioperm_active                                 14       3     -11
> init_task                                    916     904     -12
> flush_thread                                 168     149     -19
> cpu_init                                     364     339     -25
> __drop_fpu                                    60       -     -60
> ioperm_get                                    92       6     -86
> exit_thread                                  105      10     -95
> sys_iopl                                     106       -    -106
> copy_thread                                  364     257    -107
> __switch_to_xtra                             234     123    -111
> sys_ioperm                                   240       -    -240
> init_tss                                    8576     384   -8192
>
> Signed-off-by: Josh Triplett <josh at joshtriplett.org>
> ---
> v3: Eliminated several #ifdefs, and in particular almost all #ifdefs in
>     .c files, by adding a macro INIT_SET_IOPL_MASK to use in place of
>     the initializer for set_iopl_mask, and using __maybe_unused rather
>     than wrapping function definitions in #ifdef.  Rebased on v3.18-rc1.
>     Recomputed bloat-o-meter.
>
> I assume this should go through the x86 tree rather than the tiny tree.
>
>  arch/x86/Kconfig                      | 10 +++++
>  arch/x86/include/asm/paravirt.h       |  2 +
>  arch/x86/include/asm/paravirt_types.h |  5 +++
>  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          | 13 ++-----
>  arch/x86/kernel/process_64.c          |  2 +-
>  arch/x86/kernel/ptrace.c              |  8 ++++
>  arch/x86/xen/enlighten.c              |  4 +-
>  drivers/tty/vt/vt_ioctl.c             |  2 +-
>  kernel/sys_ni.c                       |  5 +++
>  17 files changed, 169 insertions(+), 67 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f2327e8..a7de2eb 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -984,6 +984,16 @@ config X86_ESPFIX64
>         def_bool y
>         depends on X86_16BIT && X86_64
>
> +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 software that drives hardware directly from userspace
> +         without using a 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 cd6e161..52d2ec8 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 7549b8b..a22a5d4 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -142,7 +142,12 @@ 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);
> +#define INIT_SET_IOPL_MASK(f) .set_iopl_mask = f,
> +#else
> +#define INIT_SET_IOPL_MASK(f)
> +#endif
>
>         void (*wbinvd)(void);
>         void (*io_delay)(void);
> diff --git a/arch/x86/include/asm/processor.h
b/arch/x86/include/asm/processor.h
> index 76751cd..6e0b639 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -255,7 +255,11 @@ 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
>   */
> @@ -510,11 +534,13 @@ 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 */
>         /*
>          * fpu_counter contains the number of consecutive context switches
>          * that the FPU is used. If this is over a threshold, the lazy fpu
> @@ -531,7 +557,7 @@ struct thread_struct {
>   */
>  static inline void native_set_iopl_mask(unsigned mask)
>  {
> -#ifdef CONFIG_X86_32
> +#if defined(CONFIG_X86_IOPORT) && defined(CONFIG_X86_32)
>         unsigned int reg;
>
>         asm volatile ("pushfl;"
> @@ -842,12 +868,8 @@ 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
> @@ -855,6 +877,19 @@ 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, \
> @@ -862,7 +897,7 @@ 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 8f1e774..84d5fbe 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 4b4f78c..ae2e8d7 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1297,7 +1297,6 @@ void cpu_init(void)
>         struct tss_struct *t;
>         unsigned long v;
>         int cpu = stack_smp_processor_id();
> -       int i;
>
>         wait_for_master_cpu(cpu);
>
> @@ -1357,14 +1356,7 @@ 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;
> @@ -1419,7 +1411,7 @@ 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 df088bb..1e6a74e0 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -609,6 +609,11 @@ 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
> @@ -621,10 +626,8 @@ 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 548d25f..e7969d4 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -383,7 +383,7 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
>         .iret = native_iret,
>         .swapgs = native_swapgs,
>
> -       .set_iopl_mask = native_set_iopl_mask,
> +       INIT_SET_IOPL_MASK(native_set_iopl_mask)
>         .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 */
> +}
Personally, I prefer seeing these kinds of optional functions declared
in a single block rather than having the #ifdefs inside the functions:

#ifdef 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)
{
    ...
}

...remaining_functions...

#else
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;
}
...remaining functions...
#endif /* CONFIG_X86_IOPORT */

But this is entirely a style decision, so I leave it up to the x86
maintainers ...

Another nit may be that we should call this CONFIG_SYSCALL_IOPL or
CONFIG_SYSCALL_IOPERM in keeping with the other CONFIG_SYSCALL_*
naming thread? Again, I don't really care strongly beyond really
wanting to use this new feature! :)

Thanks for working on this!

-Kees
> +
>  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 e127dda..7ac01bf 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
> @@ -104,23 +106,7 @@ 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);
>  }
>
> @@ -225,19 +211,7 @@ 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 07550ff..3b82293 100644
> --- a/arch/x86/kernel/process_32.c
> +++ b/arch/x86/kernel/process_32.c
> @@ -154,7 +154,7 @@ int copy_thread(unsigned long clone_flags, unsigned
long sp,
>                 childregs->orig_ax = -1;
>                 childregs->cs = __KERNEL_CS | get_kernel_rpl();
>                 childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
> -               p->thread.io_bitmap_ptr = NULL;
> +               clear_thread_io_bitmap(p);
>                 return 0;
>         }
>         *childregs = *current_pt_regs();
> @@ -165,7 +165,7 @@ int copy_thread(unsigned long clone_flags, unsigned
long sp,
>         p->thread.ip = (unsigned long) ret_from_fork;
>         task_user_gs(p) = get_user_gs(current_pt_regs());
>
> -       p->thread.io_bitmap_ptr = NULL;
> +       clear_thread_io_bitmap(p);
>         tsk = current;
>
>         /*
> @@ -265,14 +265,7 @@ __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);
>
>         /*
>          * If it were not for PREEMPT_ACTIVE we could guarantee that the
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index b1babb4..d18f3fc 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -164,7 +164,7 @@ int copy_thread(unsigned long clone_flags, unsigned
long sp,
>         p->thread.sp = (unsigned long) childregs;
>         p->thread.usersp = me->thread.usersp;
>         set_tsk_thread_flag(p, TIF_FORK);
> -       p->thread.io_bitmap_ptr = NULL;
> +       clear_thread_io_bitmap(p);
>
>         savesegment(gs, p->thread.gsindex);
>         p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs;
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index 749b0e4..fdb74a8 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 1a3f044..8ad0778 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -912,7 +912,7 @@ static void xen_load_sp0(struct tss_struct *tss,
>         xen_mc_issue(PARAVIRT_LAZY_CPU);
>  }
>
> -static void xen_set_iopl_mask(unsigned mask)
> +static void __maybe_unused xen_set_iopl_mask(unsigned mask)
>  {
>         struct physdev_set_iopl set_iopl;
>
> @@ -1279,7 +1279,7 @@ static const struct pv_cpu_ops xen_cpu_ops
__initconst = {
>         .write_idt_entry = xen_write_idt_entry,
>         .load_sp0 = xen_load_sp0,
>
> -       .set_iopl_mask = xen_set_iopl_mask,
> +       INIT_SET_IOPL_MASK(xen_set_iopl_mask)
>         .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 02aa418..f3014fe 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -224,3 +224,8 @@ cond_syscall(sys_seccomp);
>
>  /* access BPF programs and maps */
>  cond_syscall(sys_bpf);
> +
> +/* userspace I/O port access */
> +cond_syscall(stub_iopl);
> +cond_syscall(sys_iopl);
> +cond_syscall(sys_ioperm);
> --
> 2.1.1
>


-- 
Kees Cook
Chrome OS Security

On Wed, 29 Oct 2014, Josh Triplett wrote:
> v3: Eliminated several #ifdefs, and in particular almost all #ifdefs in
>     .c files, by adding a macro INIT_SET_IOPL_MASK to use in place of
>     the initializer for set_iopl_mask, and using __maybe_unused rather
>     than wrapping function definitions in #ifdef.  Rebased on v3.18-rc1.
>     Recomputed bloat-o-meter.
Can you please split this patch into smaller pieces?

    - Seperate the code move to header files
    - Seperate the macro stuff
    - Add the #ifdef CONFIG_.... changes

Thanks,

	tglx