On Mon, Jun 12, 2023 at 05:10:27PM -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: ^ mapping? > 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. > > Start the process by renaming pte_mkwrite() to pte_mkwrite_novma() and > adding the pte_mkwrite() wrapper in linux/pgtable.h. Apply the same > pattern for pmd_mkwrite(). Since not all archs have a pmd_mkwrite_novma(), > create a new arch config HAS_HUGE_PAGE that can be used to tell if > pmd_mkwrite() should be defined. Otherwise in the !HAS_HUGE_PAGE cases the > compiler would not be able to find pmd_mkwrite_novma(). > > No functional change. > > Cc: linux-...@vger.kernel.org > Cc: linux-ker...@vger.kernel.org > Cc: linux-al...@vger.kernel.org > Cc: linux-snps-...@lists.infradead.org > Cc: linux-arm-ker...@lists.infradead.org > Cc: linux-c...@vger.kernel.org > Cc: linux-hexa...@vger.kernel.org > Cc: linux-i...@vger.kernel.org > Cc: loonga...@lists.linux.dev > Cc: linux-m...@lists.linux-m68k.org > Cc: Michal Simek <mon...@monstr.eu> > Cc: Dinh Nguyen <dingu...@kernel.org> > Cc: linux-m...@vger.kernel.org > Cc: openr...@lists.librecores.org > Cc: linux-par...@vger.kernel.org > Cc: linuxppc-...@lists.ozlabs.org > Cc: linux-ri...@lists.infradead.org > Cc: linux-s...@vger.kernel.org > Cc: linux...@vger.kernel.org > Cc: sparcli...@vger.kernel.org > Cc: linux-um@lists.infradead.org > Cc: linux-a...@vger.kernel.org > Cc: linux...@kvack.org > Suggested-by: Linus Torvalds <torva...@linuxfoundation.org> > Signed-off-by: Rick Edgecombe <rick.p.edgeco...@intel.com> > Link: > https://lore.kernel.org/lkml/CAHk-=wizjsu7c9sfyzb3q04108stghff2wfbokgccgw7riz...@mail.gmail.com/ Reviewed-by: Mike Rapoport (IBM) <r...@kernel.org> -- Sincerely yours, Mike. _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um
