Re: [PATCH v6 18/41] mm: Introduce VM_SHADOW_STACK for shadow stack memory
From: David Hildenbrand <hidden>
Date: 2023-02-20 12:57:02
Also in:
linux-api, linux-doc, linux-mm, lkml
On 18.02.23 22:14, Rick Edgecombe wrote:
From: Yu-cheng Yu <redacted> 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.
I suggest simplifying and abstracting that description. "New hardware extensions implement support for shadow stack memory, such as x86 Control-flow Enforcement Technology (CET). Let's add a new VM flag to identify these areas, for example, to be used to properly indicate shadow stack PTEs to the hardware."
Reviewed-by: Kees Cook <redacted>
Tested-by: Pengfei Xu <redacted>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Yu-cheng Yu <redacted>
Reviewed-by: Kirill A. Shutemov <redacted>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Kees Cook <redacted>
---
v6:
- Add comment about VM_SHADOW_STACK not being allowed with VM_SHARED
(David Hildenbrand)Might want to add some more meat to the patch description why that is the case.
quoted hunk ↗ jump to hunk
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 e224b6d5b642..115843e8cce3 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst@@ -564,6 +564,7 @@ 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 willdiff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index af1c49ae11b1..9e2cefe47749 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c@@ -711,6 +711,9 @@ 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 e6f1789c8e69..76e0a09aeffe 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h@@ -315,11 +315,13 @@ 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@@ -335,6 +337,12 @@ extern unsigned int kobjsize(const void *objp); #endif #endif /* CONFIG_ARCH_HAS_PKEYS */ +#ifdef CONFIG_X86_USER_SHADOW_STACK
Should we abstract this to CONFIG_ARCH_USER_SHADOW_STACK, seeing that other architectures might similarly need it? -- Thanks, David / dhildenb