On Tue, Mar 16, 2021 at 08:10:41AM -0700, Yu-cheng Yu wrote:

When serving a page fault, maybe_mkwrite() makes a PTE writable if its vma
has VM_WRITE.

A shadow stack vma has VM_SHSTK.  Its PTEs have _PAGE_DIRTY, but not
_PAGE_WRITE.  In fork(), _PAGE_DIRTY is cleared to effect copy-on-write,

						  to cause

and in page fault, _PAGE_DIRTY is restored and the shadow stack page is

      in the page fault handler...

writable again.

Update maybe_mkwrite() by introducing arch_maybe_mkwrite(), which sets
_PAGE_DIRTY for a shadow stack PTE.

Apply the same changes to maybe_pmd_mkwrite().

Signed-off-by: Yu-cheng Yu <redacted>
Reviewed-by: Kees Cook <redacted>
---
 arch/x86/Kconfig        |  4 ++++
 arch/x86/mm/pgtable.c   | 18 ++++++++++++++++++
 include/linux/mm.h      |  2 ++
 include/linux/pgtable.h | 24 ++++++++++++++++++++++++
 mm/huge_memory.c        |  2 ++
 5 files changed, 50 insertions(+)

Looks straightforward to me but I guess it needs a mm person's ack.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette