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Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Florian Weimer , Christian Brauner , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v8 23/38] arm64/signal: Set up and restore the GCS context for signal handlers In-reply-to: <20240203-arm64-gcs-v8-23-c9fec77673ef@kernel.org> Date: Mon, 19 Feb 2024 23:03:46 -0300 Message-ID: <87zfvv7uyl.fsf@linaro.org> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240219_180353_334296_A63899B2 X-CRM114-Status: GOOD ( 14.56 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Mark Brown writes: > +#ifdef CONFIG_ARM64_GCS > +static int gcs_restore_signal(void) > +{ > + u64 gcspr_el0, cap; > + int ret; > + > + if (!system_supports_gcs()) > + return 0; > + > + if (!(current->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE)) > + return 0; > + > + gcspr_el0 = read_sysreg_s(SYS_GCSPR_EL0); > + > + /* > + * GCSPR_EL0 should be pointing at a capped GCS, read the cap... > + */ > + gcsb_dsync(); > + ret = copy_from_user(&cap, (__user void*)gcspr_el0, sizeof(cap)); > + if (ret) > + return -EFAULT; > + > + /* > + * ...then check that the cap is the actual GCS before > + * restoring it. > + */ > + if (!gcs_signal_cap_valid(gcspr_el0, cap)) > + return -EINVAL; > + > + /* Invalidate the token to prevent reuse */ > + put_user_gcs(0, (__user void*)gcspr_el0, &ret); > + if (ret != 0) > + return -EFAULT; You had mentioned that "ideally we'd be doing a compare and exchange here to substitute in a zero". Is a compare and exchange not necessary anymore, or is it just being left for later? In the latter case, a TODO or FIXME comment mentioning it would be useful here. > + > + current->thread.gcspr_el0 = gcspr_el0 + sizeof(cap); > + write_sysreg_s(current->thread.gcspr_el0, SYS_GCSPR_EL0); > + > + return 0; > +} -- Thiago _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv