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Subject[PATCH v10 12/26] mm: Introduce VM_SHSTK for shadow stack memory
Date
A Shadow Stack PTE must be read-only and have _PAGE_DIRTY set.  However,
read-only and Dirty PTEs also exist for copy-on-write (COW) pages. These
two cases are handled differently for page faults. Introduce VM_SHSTK to
track shadow stack VMAs.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
v9:
- Add VM_SHSTK case to arch_vma_name().
- Revise the commit log to explain why adding a new VM flag.

arch/x86/mm/mmap.c | 2 ++
fs/proc/task_mmu.c | 3 +++
include/linux/mm.h | 8 ++++++++
3 files changed, 13 insertions(+)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index cb91eccc4960..fe77fd6debf1 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -163,6 +163,8 @@ unsigned long get_mmap_base(int is_legacy)

const char *arch_vma_name(struct vm_area_struct *vma)
{
+ if (vma->vm_flags & VM_SHSTK)
+ return "[shadow stack]";
return NULL;
}

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 8d382d4ec067..434692759265 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -657,6 +657,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
[ilog2(VM_PKEY_BIT4)] = "",
#endif
#endif /* CONFIG_ARCH_HAS_PKEYS */
+#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
+ [ilog2(VM_SHSTK)] = "ss",
+#endif
};
size_t i;

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5a323422d783..54bb4cd9fee8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -294,11 +294,13 @@ extern unsigned int kobjsize(const void *objp);
#define VM_HIGH_ARCH_BIT_2 34 /* bit only usable on 64-bit architectures */
#define VM_HIGH_ARCH_BIT_3 35 /* bit only usable on 64-bit architectures */
#define VM_HIGH_ARCH_BIT_4 36 /* bit only usable on 64-bit architectures */
+#define VM_HIGH_ARCH_BIT_5 37 /* bit only usable on 64-bit architectures */
#define VM_HIGH_ARCH_0 BIT(VM_HIGH_ARCH_BIT_0)
#define VM_HIGH_ARCH_1 BIT(VM_HIGH_ARCH_BIT_1)
#define VM_HIGH_ARCH_2 BIT(VM_HIGH_ARCH_BIT_2)
#define VM_HIGH_ARCH_3 BIT(VM_HIGH_ARCH_BIT_3)
#define VM_HIGH_ARCH_4 BIT(VM_HIGH_ARCH_BIT_4)
+#define VM_HIGH_ARCH_5 BIT(VM_HIGH_ARCH_BIT_5)
#endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */

#ifdef CONFIG_ARCH_HAS_PKEYS
@@ -336,6 +338,12 @@ extern unsigned int kobjsize(const void *objp);
# define VM_MPX VM_NONE
#endif

+#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
+# define VM_SHSTK VM_HIGH_ARCH_5
+#else
+# define VM_SHSTK VM_NONE
+#endif
+
#ifndef VM_GROWSUP
# define VM_GROWSUP VM_NONE
#endif
--
2.21.0
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