Re: [PATCH v4 21/39] mm/mprotect: Exclude shadow stack from preserve_write

Kees Cook
2022-12-03T02:38:37Z

On Fri, Dec 02, 2022 at 04:35:48PM -0800, Rick Edgecombe wrote:
> 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.
>
> In change_pte_range(), when a PTE is changed for prot_numa, _PAGE_RW is
> preserved to avoid the additional write fault after the NUMA hinting fault.
> However, pte_write() now includes both normal writable and shadow stack
> (Write=0, Dirty=1) PTEs, but the latter does not have _PAGE_RW and has no
> need to preserve it.
>
> Exclude shadow stack from preserve_write test, and apply the same change to
> change_huge_pmd().
>
> 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: Kees Cook <keescook@chromium.org>

--
Kees Cook