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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 , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , Weijiang Yang , "Kirill A . Shutemov" , John Allen , kcc@google.com, eranian@google.com, jamorris@linux.microsoft.com, dethoma@microsoft.com, akpm@linux-foundation.org, Andrew.Cooper3@citrix.com, christina.schimpe@intel.com, david@redhat.com, debug@rivosinc.com, szabolcs.nagy@arm.com, torvalds@linux-foundation.org, broonie@kernel.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH v9 02/42] mm: Move pte/pmd_mkwrite() callers with no VMA to _novma() Message-ID: <20230613074428.GS52412@kernel.org> References: <20230613001108.3040476-1-rick.p.edgecombe@intel.com> <20230613001108.3040476-3-rick.p.edgecombe@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230613001108.3040476-3-rick.p.edgecombe@intel.com> X-Stat-Signature: 5aur78cz4x8x5huf39u1k4bxrac53czk X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 5F83280004 X-Rspam-User: X-HE-Tag: 1686642309-629850 X-HE-Meta: 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 /FRe4nYd 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jun 12, 2023 at 05:10:28PM -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. > > Previous patches have done the first step, so next move the callers that > don't have a VMA to pte_mkwrite_novma(). Also do the same for I hear x86 maintainers asking to drop "previous patches" ;-) Maybe This is the second step of the conversion that moves the callers ... > pmd_mkwrite(). This will be ok for the shadow stack feature, as these > callers are on kernel memory which will not need to be made shadow stack, > and the other architectures only currently support one type of memory > in pte_mkwrite() > > 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 > Signed-off-by: Rick Edgecombe Reviewed-by: Mike Rapoport (IBM) -- Sincerely yours, Mike.