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b=kxfkBm24tZLUhSzuj1G9mlNxxOsSkyEYKXhboHPkPONc5qOzT++VqXm0Q2glImzWi Aavyw9UfxCSIjZcJyQqu1SCP/l+VUQTpbja9KWMnCdTAUZYmScN0jPP+PLk++7mW/x ow1H1GE5sIDv41GwED6cxHcnm6VHsq8SvQKIx9Yw= Date: Wed, 27 Dec 2023 14:24:41 -0800 From: Andrew Morton To: Deepak Gupta Cc: rick.p.edgecombe@intel.com, broonie@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] mm: abstract shadow stack vma behind arch_is_shadow_stack_vma Message-Id: <20231227142441.f9a76fa3c8b9b79eea8f93a2@linux-foundation.org> In-Reply-To: References: <20231222235248.576482-1-debug@rivosinc.com> <20231227134514.13629032c39decdf1dddcc75@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 7E572C0006 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: xza944uuqs8mbu6qgfceb3tik9poba65 X-HE-Tag: 1703715886-986454 X-HE-Meta: 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 C8a1AtbD B1gDt 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: List-Subscribe: List-Unsubscribe: On Wed, 27 Dec 2023 14:20:36 -0800 Deepak Gupta wrote: > On Wed, Dec 27, 2023 at 1:45 PM Andrew Morton wrote: > > > > On Fri, 22 Dec 2023 15:51:04 -0800 Deepak Gupta wrote: > > > > > x86 has used VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) to encode shadow > > > stack VMA. VM_SHADOW_STACK is thus not possible on 32bit. Some arches may > > > need a way to encode shadow stack on 32bit and 64bit both and they may > > > encode this information differently in VMAs. > > > > Is such a patch in the pipeline? Otherwise we're making a change that > > serves no purpose. > > Yes I do have patches in the pipeline for riscv. > On riscv, presence of only `VM_WRITE` (i.e. (flags & (VM_READ | > VM_WRITE | VM_EXEC)) > == VM_WRITE) would mean a shadow stack. > And yes there would be relevant patches to ensure that existing consumers using > `PROT_WRITE` gets translated to (VM_WRITE | VM_READ) OK, please plan to carry this patch in whatever tree contains the above.