On Thu, Sep 29, 2022 at 03:29:14PM -0700, Rick Edgecombe wrote:

From: Yu-cheng Yu <redacted>

With the introduction of shadow stack memory there are two ways a pte can
be writable: regular writable memory and shadow stack memory.

In past patches, maybe_mkwrite() has been updated to apply pte_mkwrite()
or pte_mkwrite_shstk() depending on the VMA flag. This covers most cases
where a PTE is made writable. However, there are places where pte_mkwrite()
is called directly and the logic should now also create a shadow stack PTE
in the case of a shadow stack VMA.

 - do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE
   directly and call pte_mkwrite(), which is the same as maybe_mkwrite()
   in logic and intention. Just change them to maybe_mkwrite().

 - When userfaultfd is creating a PTE after userspace handles the fault
   it calls pte_mkwrite() directly. Teach it about pte_mkwrite_shstk()

In other cases where pte_mkwrite() is called directly, the VMA will not
be VM_SHADOW_STACK, and so shadow stack memory should not be created.
 - In the case of pte_savedwrite(), shadow stack VMA's are excluded.
 - In the case of the "dirty_accountable" optimization in mprotect(),
   shadow stack VMA's won't be VM_SHARED, so it is not nessary.

Signed-off-by: Yu-cheng Yu <redacted>

Reviewed-by: Kees Cook <redacted>

-- 
Kees Cook