linux-kernel - Re: [PATCH v7 25/39] arm64/signal: Expose GCS state in signal frames

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Message-ID: <87sf4bf1tm.fsf@linaro.org>
Date:   Sat, 09 Dec 2023 19:28:21 -0300
From:   Thiago Jung Bauermann <thiago.bauermann@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Deepak Gupta <debug@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Florian Weimer <fweimer@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v7 25/39] arm64/signal: Expose GCS state in signal frames


Mark Brown <broonie@...nel.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