[PATCH v3 14/37] mm: Introduce VM_SHADOW_STACK for shadow stack memory

Rick Edgecombe
2022-11-04T22:41:39Z

From: Yu-cheng Yu <yu-cheng.yu@intel.com>

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual properties, which requires some core mm changes to function
properly.

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.

Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Kees Cook <keescook@chromium.org>

---

v3:
- Drop arch specific change in arch_vma_name(). The memory can show as
anonymous (Kirill)
- Change CONFIG_ARCH_HAS_SHADOW_STACK to CONFIG_X86_USER_SHADOW_STACK
in show_smap_vma_flags() (Boris)

Documentation/filesystems/proc.rst | 1 +
fs/proc/task_mmu.c | 3 +++
include/linux/mm.h | 8 ++++++++
3 files changed, 12 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 898c99eae8e4..05506dfa0480 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -560,6 +560,7 @@ encoded manner. The codes are the following:
mt arm64 MTE allocation tags are enabled
um userfaultfd missing tracking
uw userfaultfd wr-protect tracking
+ ss shadow stack page
== =======================================

Note that there is no guarantee that every flag and associated mnemonic will
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 8a74cdcc9af0..7dee7afbb01b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -703,6 +703,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
[ilog2(VM_UFFD_MINOR)] = "ui",
#endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
+#ifdef CONFIG_X86_USER_SHADOW_STACK
+ [ilog2(VM_SHADOW_STACK)] = "ss",
+#endif
};
size_t i;

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5314ad0a342d..42c4e4bc972d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -314,11 +314,13 @@ 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
@@ -334,6 +336,12 @@ extern unsigned int kobjsize(const void *objp);
#endif
#endif /* CONFIG_ARCH_HAS_PKEYS */

+#ifdef CONFIG_X86_USER_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)
--
2.17.1