[PATCH v24 13/30] mm: Introduce VM_SHADOW_STACK for shadow stack memory

[Yu-cheng Yu]

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_SHADOW_STACK to track shadow stack VMAs.

Signed-off-by: Yu-cheng Yu <yu-cheng...@intel.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
---
v24:
- Change VM_SHSTK to VM_SHADOW_STACK.
- Change CONFIG_X86_CET to CONFIG_X86_SHADOW_STACK to reflect Kconfig changes.

 Documentation/filesystems/proc.rst | 1 +
 arch/x86/mm/mmap.c                 | 2 ++
 fs/proc/task_mmu.c                 | 3 +++
 include/linux/mm.h                 | 8 ++++++++
 4 files changed, 14 insertions(+)

diff --git a/Documentation/filesystems/proc.rst 
b/Documentation/filesystems/proc.rst
index 48fbfc336ebf..5d8a2d75c799 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -549,6 +549,7 @@ encoded manner. The codes are the following:
     mg    mergable advise flag
     bt    arm64 BTI guarded page
     mt    arm64 MTE allocation tags are enabled
+    ss    shadow stack page
     ==    =======================================
 
 Note that there is no guarantee that every flag and associated mnemonic will
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index c90c20904a60..f3f52c5e2fd6 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -165,6 +165,8 @@ unsigned long get_mmap_base(int is_legacy)
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
+       if (vma->vm_flags & VM_SHADOW_STACK)
+               return "[shadow stack]";
        return NULL;
 }
 
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index e862cab69583..0aa57de9dfab 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -661,6 +661,9 @@ 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_ARCH_HAS_SHADOW_STACK
+               [ilog2(VM_SHADOW_STACK)]= "ss",
+#endif
        };
        size_t i;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ba434287387..08282eb2f195 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -312,11 +312,13 @@ 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
@@ -332,6 +334,12 @@ extern unsigned int kobjsize(const void *objp);
 #endif
 #endif /* CONFIG_ARCH_HAS_PKEYS */
 
+#ifdef CONFIG_X86_SHADOW_STACK
+# define VM_SHADOW_STACK       VM_HIGH_ARCH_5
+#else
+# define VM_SHADOW_STACK       VM_NONE
+#endif
+
 #if defined(CONFIG_X86)
 # define VM_PAT                VM_ARCH_1       /* PAT reserves whole VMA at 
once (x86) */
 #elif defined(CONFIG_PPC)
-- 
2.21.0