Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:1 as permitted sender) client-ip=2620:137:e000::3:1;
References: <20231122-arm64-gcs-v7-0-201c483bd775@kernel.org>
 <20231122-arm64-gcs-v7-25-201c483bd775@kernel.org>
User-agent: mu4e 1.10.8; emacs 29.1
From:   Thiago Jung Bauermann <thiago.bauermann@linaro.org>
To:     Mark Brown <broonie@kernel.org>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Arnd Bergmann <arnd@arndb.de>, Oleg Nesterov <oleg@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Shuah Khan <shuah@kernel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
        Deepak Gupta <debug@rivosinc.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Florian Weimer <fweimer@redhat.com>,
        Christian Brauner <brauner@kernel.org>,
        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 v7 25/39] arm64/signal: Expose GCS state in signal frames
In-reply-to: <20231122-arm64-gcs-v7-25-201c483bd775@kernel.org>
Date:   Sat, 09 Dec 2023 19:28:21 -0300
Message-ID: <87sf4bf1tm.fsf@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk


Mark Brown <broonie@kernel.org> writes:

> +static int preserve_gcs_context(struct gcs_context __user *ctx)
> +{
> +	int err = 0;
> +	u64 gcspr;
> +
> +	/*
> +	 * We will add a cap token to the frame, include it in the
> +	 * GCSPR_EL0 we report to support stack switching via
> +	 * sigreturn.
> +	 */
> +	gcs_preserve_current_state();
> +	gcspr = current->thread.gcspr_el0;
> +	if (task_gcs_el0_enabled(current))
> +		gcspr -= 8;
> +
> +	__put_user_error(GCS_MAGIC, &ctx->head.magic, err);
> +	__put_user_error(sizeof(*ctx), &ctx->head.size, err);
> +	__put_user_error(gcspr, &ctx->gcspr, err);
> +	__put_user_error(current->thread.gcs_el0_mode,
> +			 &ctx->features_enabled, err);

Other preserve_<foo>_context() functions zero the reserved fields in
ctx. I suggest doing the same here. It helps with backward
compatibility.

> +
> +	return err;
> +}


-- 
Thiago