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

[David Hildenbrand <david@redhat.com>]

On 19.02.23 21:38, Kees Cook wrote:
> 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@vger.kernel.org
>> Cc: linux-arm-kernel@lists.infradead.org
>> Cc: linux-s390@vger.kernel.org
>> Cc: xen-devel@lists.xenproject.org
>> Cc: linux-arch@vger.kernel.org
>> Cc: linux-mm@kvack.org
>> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> 
> 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.

Right. We could pass the vm flags instead, but not sure if that really 
improves the situation. So unless someone has a better idea, this LGTM.

-- 
Thanks,

David / dhildenb