On Sat, Feb 18, 2023 at 01:14:03PM -0800, Rick Edgecombe wrote: > 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. > > One of these changes is to allow for pte_mkwrite() to create different > types of writable memory (the existing conventionally writable type and > also the new shadow stack type). Future patches will convert pte_mkwrite() > to take a VMA in order to facilitate this, however there are places in the > kernel where pte_mkwrite() is called outside of the context of a VMA. > These are for kernel memory. So create a new variant called > pte_mkwrite_kernel() and switch the kernel users over to it. Have > pte_mkwrite() and pte_mkwrite_kernel() be the same for now. Future patches > will introduce changes to make pte_mkwrite() take a VMA. > > Only do this for architectures that need it because they call pte_mkwrite() > in arch code without an associated VMA. Since it will only currently be > used in arch code, so do not include it in arch_pgtable_helpers.rst. > > Cc: linux-doc@xxxxxxxxxxxxxxx > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > Cc: linux-s390@xxxxxxxxxxxxxxx > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx > Cc: linux-arch@xxxxxxxxxxxxxxx > Cc: linux-mm@xxxxxxxxx > Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx> > Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> I think it's a little weird that it's the only PTE helper taking a vma, but it does seem like the right approach. Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
