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Message-ID: <87zfvv7uyl.fsf@linaro.org>
Date: Mon, 19 Feb 2024 23:03:46 -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 v8 23/38] arm64/signal: Set up and restore the GCS
context for signal handlers
Mark Brown <broonie@...nel.org> 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
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