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

On Fri, Dec 02, 2022 at 04:35:48PM -0800, 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.

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 <redacted>
Tested-by: John Allen <john.allen@amd.com>
Signed-off-by: Yu-cheng Yu <redacted>

Reviewed-by: Kees Cook <redacted>

-- 
Kees Cook