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Wed, 28 Aug 2024 17:17:21 -0700 (PDT) Date: Wed, 28 Aug 2024 17:17:19 -0700 From: Deepak Gupta To: Alistair Francis Cc: qemu-riscv@nongnu.org, qemu-devel@nongnu.org, palmer@dabbelt.com, Alistair.Francis@wdc.com, laurent@vivier.eu, bmeng.cn@gmail.com, liwei1518@gmail.com, dbarboza@ventanamicro.com, zhiwei_liu@linux.alibaba.com, jim.shu@sifive.com, andy.chiu@sifive.com, kito.cheng@sifive.com, Richard Henderson Subject: Re: [PATCH v11 13/20] target/riscv: mmu changes for zicfiss shadow stack protection Message-ID: References: <20240828174739.714313-1-debug@rivosinc.com> <20240828174739.714313-14-debug@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=2607:f8b0:4864:20::d29; envelope-from=debug@rivosinc.com; helo=mail-io1-xd29.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01, T_SPF_TEMPERROR=0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Aug 29, 2024 at 10:03:04AM +1000, Alistair Francis wrote: >On Thu, Aug 29, 2024 at 9:45 AM Deepak Gupta wrote: >> >> On Thu, Aug 29, 2024 at 09:29:49AM +1000, Alistair Francis wrote: >> >On Thu, Aug 29, 2024 at 3:49 AM Deepak Gupta wrote: >> >> >> >> prot |= PAGE_WRITE; >> >> } >> >> - if (pte & PTE_X) { >> >> + if (rwx & PTE_X) { >> >> bool mxr = false; >> >> >> >> /* >> >> @@ -1160,7 +1177,7 @@ restart: >> >> >> >> if (!((prot >> access_type) & 1)) { >> >> /* Access check failed */ >> >> - return TRANSLATE_FAIL; >> >> + return sstack_page ? TRANSLATE_PMP_FAIL : TRANSLATE_FAIL; >> > >> >Why is it a PMP error if it's a shadow stack page? >> >> A shadow stack page is readable by regular loads. >> We are making sure of that in `case PTE_W` in above switch case. >> But shadow stack page is not writeable via regular stores. And must raise >> access fault. return code `TRANSLATE_PMP_FAIL` is translated to access fault >> while raising fault. > >Ah, ok. It's worth commenting that we are returning TRANSLATE_PMP_FAIL >as that will be translated to an access fault Ack. > >Alistair > >> >> > >> >Alistair