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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 Content-Type: text/plain X-Rspamd-Queue-Id: DC74B40018 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: p933m4xezqhy554z44a6tpwchfe9gap5 X-HE-Tag: 1708394629-73396 X-HE-Meta: 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 uXCvTZdO SVqS2uHug8mB0Crk34Es+4zjWNECxyXqmloYHy5y8Y736k41TktQNBmsW8GsbVIqJTqGQUEp0bKal8A7nPHB4GABDZaMbddjCSeJGFGPIX7THdNxvrU6qfN2ADV1d90e30935QvaF1jzruZjsdiwvIT8bkJX537r5epuqjCaKOBh5WL+8oznqErnUFy/VCw6BHzAPqDv9S/6W7FZWdovODRA1a/M8DTPbUr9d6INWLiyz/PZWvugCEXY24SmFBGfTchtqbwwttF5N+w7+wp6M5QwdXnV9KreB/7udyhHIAFdtU8LWVenTzwBNfG83f1uXwL/eH3Ux+Y69BifMjIHFu+AXlwXLyFsWTCcIuZ7w2tiuyzh8I35OVX1GcERmyy7ZPLxPOxmz2NMPb0PajPul/tDwmRQpQdVFN3BlA5XY/ICUDCwBUgawbIFS+ldn0o3aC1JfrXggW42MwircLbhO486ADg== 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: 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