From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Subject: Re: [PATCH v9 01/42] mm: Rename arch pte_mkwrite()'s to pte_mkwrite_novma() Date: Tue, 13 Jun 2023 09:19:32 +0200 Message-ID: References: <20230613001108.3040476-1-rick.p.edgecombe@intel.com> <20230613001108.3040476-2-rick.p.edgecombe@intel.com> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20230613001108.3040476-2-rick.p.edgecombe@intel.com> List-ID: Content-Type: text/plain; charset="windows-1252" To: Rick Edgecombe Cc: x86@kernel.org, "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H . J . Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit On Tue, Jun 13, 2023 at 2:13=E2=80=AFAM 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 requir= es > 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. > > 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-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: linux-alpha@vger.kernel.org > Cc: linux-snps-arc@lists.infradead.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-csky@vger.kernel.org > Cc: linux-hexagon@vger.kernel.org > Cc: linux-ia64@vger.kernel.org > Cc: loongarch@lists.linux.dev > Cc: linux-m68k@lists.linux-m68k.org > Cc: Michal Simek > Cc: Dinh Nguyen > Cc: linux-mips@vger.kernel.org > Cc: openrisc@lists.librecores.org > Cc: linux-parisc@vger.kernel.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: linux-riscv@lists.infradead.org > Cc: linux-s390@vger.kernel.org > Cc: linux-sh@vger.kernel.org > Cc: sparclinux@vger.kernel.org > Cc: linux-um@lists.infradead.org > Cc: linux-arch@vger.kernel.org > Cc: linux-mm@kvack.org > Suggested-by: Linus Torvalds > Signed-off-by: Rick Edgecombe > Link: https://lore.kernel.org/lkml/CAHk-=3DwiZjSu7c9sFYZb3q04108stgHff2wf= bokGCCgW7riz+8Q@mail.gmail.com/ > arch/m68k/include/asm/mcf_pgtable.h | 2 +- > arch/m68k/include/asm/motorola_pgtable.h | 2 +- > arch/m68k/include/asm/sun3_pgtable.h | 2 +- Acked-by: Geert Uytterhoeven Gr{oetje,eeting}s, Geert --=20 Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k= .org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like t= hat. -- Linus Torvalds