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

[Kees Cook]

On Thu, Sep 29, 2022 at 03:29:11PM -0700, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> 
> 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@xxxxxxxxx>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  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