Re: [PATCH v2 14/39] mm: Introduce VM_SHADOW_STACK for shadow stack memory

Kees Cook
2022-10-03T18:17:26Z

On Thu, Sep 29, 2022 at 03:29:11PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@intel.com>
>
> 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.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>
> ---
> 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 e7aafc82be99..d54ff397947a 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/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;
> }

I agree with Kirill: this should be in the arch-agnostic code.

--
Kees Cook