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Rusty Russell

2007-Apr-18 13:02 UTC

[PATCH] Gerd Hoffman's move-vsyscall-into-user-address-range patch

AFAICT we'll pay one extra TLB entry for this patch.  Zach had a patch
which left the vsyscall page at the top of memory (minus hole for
hypervisor) and patched the ELF header at boot.

Thoughts welcome,
Rusty.

Name: Move vsyscall page out of fixmap, above stack
Author: Gerd Hoffmann <kraxel@suse.de>

Hypervisors want to use memory at the top of the address space
(eg. 64MB for Xen, or 168MB for Xen w/ PAE).  Creating this hole means
moving the vsyscall page away from 0xffffe000.

If we create this hole statically with a config option, we give up,
say, 256MB of lowmem for the case where a hypervisor-capable kernel is
actually running on native hardware.

If we create this hole dynamically and leave the vsyscall page at the
top of kernel memory, we would have to patch up the vsyscall elf
header at boot time to reflect where we put it.

Instead, this patch moves the vsyscall page into the user address
region, just below PAGE_OFFSET: it's still at a fixed address, but
it's not where the hypervisor wants to be, so resizing the hole is
trivial.

Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/arch/i386/kernel/asm-offsets.c
working-2.6.17-rc4-vsyscall-above-stack/arch/i386/kernel/asm-offsets.c
--- linux-2.6.17-rc4/arch/i386/kernel/asm-offsets.c	2005-07-15
04:38:36.000000000 +1000
+++ working-2.6.17-rc4-vsyscall-above-stack/arch/i386/kernel/asm-offsets.c
2006-05-16 14:24:00.000000000 +1000
@@ -13,6 +13,7 @@
 #include <asm/fixmap.h>
 #include <asm/processor.h>
 #include <asm/thread_info.h>
+#include <asm/elf.h>
 
 #define DEFINE(sym, val) \
         asm volatile("\n->" #sym " %0 " #val : :
"i" (val))
@@ -68,5 +69,5 @@ void foo(void)
 		 sizeof(struct tss_struct));
 
 	DEFINE(PAGE_SIZE_asm, PAGE_SIZE);
-	DEFINE(VSYSCALL_BASE, __fix_to_virt(FIX_VSYSCALL));
+	DEFINE(VSYSCALL_BASE, VSYSCALL_BASE);
 }
diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/arch/i386/kernel/sysenter.c
working-2.6.17-rc4-vsyscall-above-stack/arch/i386/kernel/sysenter.c
--- linux-2.6.17-rc4/arch/i386/kernel/sysenter.c	2006-03-23 12:42:01.000000000
+1100
+++ working-2.6.17-rc4-vsyscall-above-stack/arch/i386/kernel/sysenter.c
2006-05-16 14:27:05.000000000 +1000
@@ -13,6 +13,7 @@
 #include <linux/gfp.h>
 #include <linux/string.h>
 #include <linux/elf.h>
+#include <linux/mm.h>
 
 #include <asm/cpufeature.h>
 #include <asm/msr.h>
@@ -45,23 +46,88 @@ void enable_sep_cpu(void)
  */
 extern const char vsyscall_int80_start, vsyscall_int80_end;
 extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
+static void *syscall_page;
 
 int __init sysenter_setup(void)
 {
-	void *page = (void *)get_zeroed_page(GFP_ATOMIC);
-
-	__set_fixmap(FIX_VSYSCALL, __pa(page), PAGE_READONLY_EXEC);
+	syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
 
 	if (!boot_cpu_has(X86_FEATURE_SEP)) {
-		memcpy(page,
+		memcpy(syscall_page,
 		       &vsyscall_int80_start,
 		       &vsyscall_int80_end - &vsyscall_int80_start);
 		return 0;
 	}
 
-	memcpy(page,
+	memcpy(syscall_page,
 	       &vsyscall_sysenter_start,
 	       &vsyscall_sysenter_end - &vsyscall_sysenter_start);
 
 	return 0;
 }
+
+static struct page*
+syscall_nopage(struct vm_area_struct *vma, unsigned long adr, int *type)
+{
+	struct page *p = virt_to_page(adr - vma->vm_start + syscall_page);
+	get_page(p);
+	return p;
+}
+
+/* Prevent VMA merging */
+static void syscall_vma_close(struct vm_area_struct *vma)
+{
+}
+
+static struct vm_operations_struct syscall_vm_ops = {
+	.close = syscall_vma_close,
+	.nopage = syscall_nopage,
+};
+
+/* Setup a VMA at program startup for the vsyscall page */
+int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
+{
+	struct vm_area_struct *vma;
+	struct mm_struct *mm = current->mm;
+	int ret;
+
+	vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
+	if (!vma)
+		return -ENOMEM;
+
+	memset(vma, 0, sizeof(struct vm_area_struct));
+	/* Could randomize here */
+	vma->vm_start = VSYSCALL_BASE;
+	vma->vm_end = VSYSCALL_BASE + PAGE_SIZE;
+	/* MAYWRITE to allow gdb to COW and set breakpoints */
+	vma->vm_flags = VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYEXEC|VM_MAYWRITE;
+	vma->vm_flags |= mm->def_flags;
+	vma->vm_page_prot = protection_map[vma->vm_flags & 7];
+	vma->vm_ops = &syscall_vm_ops;
+	vma->vm_mm = mm;
+
+	down_write(&mm->mmap_sem);
+	if ((ret = insert_vm_struct(mm, vma))) {
+		up_write(&mm->mmap_sem);
+		kmem_cache_free(vm_area_cachep, vma);
+		return ret;
+	}
+	mm->total_vm++;
+	up_write(&mm->mmap_sem);
+	return 0;
+}
+
+struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
+{
+	return NULL;
+}
+
+int in_gate_area(struct task_struct *task, unsigned long addr)
+{
+	return 0;
+}
+
+int in_gate_area_no_task(unsigned long addr)
+{
+	return 0;
+}
diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/arch/i386/mm/pgtable.c
working-2.6.17-rc4-vsyscall-above-stack/arch/i386/mm/pgtable.c
--- linux-2.6.17-rc4/arch/i386/mm/pgtable.c	2006-05-16 10:50:48.000000000 +1000
+++ working-2.6.17-rc4-vsyscall-above-stack/arch/i386/mm/pgtable.c	2006-05-16
14:24:47.000000000 +1000
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/pagemap.h>
 #include <linux/spinlock.h>
+#include <linux/module.h>
 
 #include <asm/system.h>
 #include <asm/pgtable.h>
@@ -138,6 +139,10 @@ void set_pmd_pfn(unsigned long vaddr, un
 	__flush_tlb_one(vaddr);
 }
 
+static int nr_fixmaps = 0;
+unsigned long __FIXADDR_TOP = 0xfffff000;
+EXPORT_SYMBOL(__FIXADDR_TOP);
+
 void __set_fixmap (enum fixed_addresses idx, unsigned long phys, pgprot_t
flags)
 {
 	unsigned long address = __fix_to_virt(idx);
@@ -147,6 +152,13 @@ void __set_fixmap (enum fixed_addresses 
 		return;
 	}
 	set_pte_pfn(address, phys >> PAGE_SHIFT, flags);
+	nr_fixmaps++;
+}
+
+void set_fixaddr_top(unsigned long top)
+{
+	BUG_ON(nr_fixmaps > 0);
+	__FIXADDR_TOP = top - PAGE_SIZE;
 }
 
 pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/include/asm-i386/a.out.h
working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/a.out.h
--- linux-2.6.17-rc4/include/asm-i386/a.out.h	2004-02-04 14:43:43.000000000
+1100
+++ working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/a.out.h	2006-05-16
14:24:47.000000000 +1000
@@ -19,7 +19,7 @@ struct exec
 
 #ifdef __KERNEL__
 
-#define STACK_TOP	TASK_SIZE
+#define STACK_TOP	(TASK_SIZE - 3*PAGE_SIZE)
 
 #endif
 
diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/include/asm-i386/elf.h
working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/elf.h
--- linux-2.6.17-rc4/include/asm-i386/elf.h	2006-03-23 12:44:01.000000000 +1100
+++ working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/elf.h	2006-05-16
14:24:47.000000000 +1000
@@ -129,11 +129,16 @@ extern int dump_task_extended_fpu (struc
 #define ELF_CORE_COPY_FPREGS(tsk, elf_fpregs) dump_task_fpu(tsk, elf_fpregs)
 #define ELF_CORE_COPY_XFPREGS(tsk, elf_xfpregs) dump_task_extended_fpu(tsk,
elf_xfpregs)
 
-#define VSYSCALL_BASE	(__fix_to_virt(FIX_VSYSCALL))
+#define VSYSCALL_BASE	(PAGE_OFFSET - 2*PAGE_SIZE)
 #define VSYSCALL_EHDR	((const struct elfhdr *) VSYSCALL_BASE)
 #define VSYSCALL_ENTRY	((unsigned long) &__kernel_vsyscall)
 extern void __kernel_vsyscall;
 
+#define ARCH_HAS_SETUP_ADDITIONAL_PAGES
+struct linux_binprm;
+extern int arch_setup_additional_pages(struct linux_binprm *bprm,
+                                       int executable_stack);
+
 #define ARCH_DLINFO						\
 do {								\
 		NEW_AUX_ENT(AT_SYSINFO,	VSYSCALL_ENTRY);	\
diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/include/asm-i386/fixmap.h
working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/fixmap.h
--- linux-2.6.17-rc4/include/asm-i386/fixmap.h	2006-03-23 12:43:10.000000000
+1100
+++ working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/fixmap.h	2006-05-16
14:24:47.000000000 +1000
@@ -20,7 +20,7 @@
  * Leave one empty page between vmalloc'ed areas and
  * the start of the fixmap.
  */
-#define __FIXADDR_TOP	0xfffff000
+extern unsigned long __FIXADDR_TOP;
 
 #ifndef __ASSEMBLY__
 #include <linux/kernel.h>
@@ -52,7 +52,6 @@
  */
 enum fixed_addresses {
 	FIX_HOLE,
-	FIX_VSYSCALL,
 #ifdef CONFIG_X86_LOCAL_APIC
 	FIX_APIC_BASE,	/* local (CPU) APIC) -- required for SMP or not */
 #endif
@@ -95,6 +94,8 @@ enum fixed_addresses {
 extern void __set_fixmap (enum fixed_addresses idx,
 					unsigned long phys, pgprot_t flags);
 
+extern void set_fixaddr_top(unsigned long top);
+
 #define set_fixmap(idx, phys) \
 		__set_fixmap(idx, phys, PAGE_KERNEL)
 /*
@@ -116,14 +117,6 @@ extern void __set_fixmap (enum fixed_add
 #define __fix_to_virt(x)	(FIXADDR_TOP - ((x) << PAGE_SHIFT))
 #define __virt_to_fix(x)	((FIXADDR_TOP - ((x)&PAGE_MASK)) >>
PAGE_SHIFT)
 
-/*
- * This is the range that is readable by user mode, and things
- * acting like user mode such as get_user_pages.
- */
-#define FIXADDR_USER_START	(__fix_to_virt(FIX_VSYSCALL))
-#define FIXADDR_USER_END	(FIXADDR_USER_START + PAGE_SIZE)
-
-
 extern void __this_fixmap_does_not_exist(void);
 
 /*
diff -urpN --exclude TAGS -X
/home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal
linux-2.6.17-rc4/include/asm-i386/page.h
working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/page.h
--- linux-2.6.17-rc4/include/asm-i386/page.h	2006-05-16 10:51:38.000000000 +1000
+++ working-2.6.17-rc4-vsyscall-above-stack/include/asm-i386/page.h	2006-05-16
14:24:47.000000000 +1000
@@ -121,7 +121,7 @@ extern int page_is_ram(unsigned long pag
 
 #define PAGE_OFFSET		((unsigned long)__PAGE_OFFSET)
 #define VMALLOC_RESERVE		((unsigned long)__VMALLOC_RESERVE)
-#define MAXMEM			(-__PAGE_OFFSET-__VMALLOC_RESERVE)
+#define MAXMEM			(__FIXADDR_TOP-__PAGE_OFFSET-__VMALLOC_RESERVE)
 #define __pa(x)			((unsigned long)(x)-PAGE_OFFSET)
 #define __va(x)			((void *)((unsigned long)(x)+PAGE_OFFSET))
 #define pfn_to_kaddr(pfn)      __va((pfn) << PAGE_SHIFT)
@@ -137,6 +137,8 @@ extern int page_is_ram(unsigned long pag
 	((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \
 		 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
 
+#define __HAVE_ARCH_GATE_AREA 1
+
 #endif /* __KERNEL__ */
 
 #include <asm-generic/memory_model.h>

-- 
 ccontrol: http://ccontrol.ozlabs.org

Ingo Molnar

2007-Apr-18 13:02 UTC

head link

[PATCH] Gerd Hoffman's move-vsyscall-into-user-address-range patch

* Rusty Russell <rusty@rustcorp.com.au> wrote:
> AFAICT we'll pay one extra TLB entry for this patch.  Zach had a patch 
> which left the vsyscall page at the top of memory (minus hole for 
> hypervisor) and patched the ELF header at boot.
i'd suggest the solution from exec-shield (which has been there for a 
long time), which also randomizes the vsyscall vma. Exploits are already 
starting to use the vsyscall page (with predictable addresses) to 
circumvent randomization, it provides 'interesting' instructions to act 
as a syscall-functionality building block. Moving that address to 
another predictable place solves the virtualization problem, but doesnt 
solve the address-space randomization problem.

	Ingo

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