Re: [PATCH v6 11/41] mm: Introduce pte_mkwrite_kernel()

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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

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