On Mon, Jun 12, 2023 at 05:10:29PM -0700, Rick Edgecombe wrote: > The x86 Shadow stack 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 unusual properties is that shadow stack memory is writable, > but only in limited ways. These limits are applied via a specific PTE > bit combination. Nevertheless, the memory is writable, and core mm code > will need to apply the writable permissions in the typical paths that > call pte_mkwrite(). Future patches will make pte_mkwrite() take a VMA, so > that the x86 implementation of it can know whether to create regular > writable memory or shadow stack memory. Nit: ^ mappings? > But there are a couple of challenges to this. Modifying the signatures of > each arch pte_mkwrite() implementation would be error prone because some > are generated with macros and would need to be re-implemented. Also, some > pte_mkwrite() callers operate on kernel memory without a VMA. > > So this can be done in a three step process. First pte_mkwrite() can be > renamed to pte_mkwrite_novma() in each arch, with a generic pte_mkwrite() > added that just calls pte_mkwrite_novma(). Next callers without a VMA can > be moved to pte_mkwrite_novma(). And lastly, pte_mkwrite() and all callers > can be changed to take/pass a VMA. > > In a previous patches, pte_mkwrite() was renamed pte_mkwrite_novma() and > callers that don't have a VMA were changed to use pte_mkwrite_novma(). So Maybe This is the third step so pte_mkwrite() was renamed to pte_mkwrite_novma() and ... > now change pte_mkwrite() to take a VMA and change the remaining callers to > pass a VMA. Apply the same changes for pmd_mkwrite(). > > No functional change. > > Suggested-by: David Hildenbrand <david@xxxxxxxxxx> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
