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Date: Wed, 21 Aug 2024 13:54:33 +0100
From: Catalin Marinas <catalin.marinas@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: 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>,
	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>, Kees Cook <kees@kernel.org>,
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Subject: Re: [PATCH v10 21/40] arm64/gcs: Implement shadow stack prctl()
 interface
Message-ID: <ZsXjiTlfLE61-jJC@arm.com>
References: <20240801-arm64-gcs-v10-0-699e2bd2190b@kernel.org>
 <20240801-arm64-gcs-v10-21-699e2bd2190b@kernel.org>
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In-Reply-To: <20240801-arm64-gcs-v10-21-699e2bd2190b@kernel.org>

On Thu, Aug 01, 2024 at 01:06:48PM +0100, Mark Brown wrote:
> Implement the architecture neutral prtctl() interface for setting the

s/prtctl/prctl/

> +int arch_set_shadow_stack_status(struct task_struct *task, unsigned long arg)
> +{
> +	unsigned long gcs, size;
> +	int ret;
> +
> +	if (!system_supports_gcs())
> +		return -EINVAL;
> +
> +	if (is_compat_thread(task_thread_info(task)))
> +		return -EINVAL;
> +
> +	/* Reject unknown flags */
> +	if (arg & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
> +		return -EINVAL;
> +
> +	ret = gcs_check_locked(task, arg);
> +	if (ret != 0)
> +		return ret;
> +
> +	/* If we are enabling GCS then make sure we have a stack */
> +	if (arg & PR_SHADOW_STACK_ENABLE) {
> +		if (!task_gcs_el0_enabled(task)) {
> +			/* Do not allow GCS to be reenabled */
> +			if (task->thread.gcs_base)
> +				return -EINVAL;
> +
> +			if (task != current)
> +				return -EBUSY;
> +
> +			size = gcs_size(0);
> +			gcs = alloc_gcs(0, size);
> +			if (!gcs)
> +				return -ENOMEM;
> +
> +			task->thread.gcspr_el0 = gcs + size - sizeof(u64);
> +			task->thread.gcs_base = gcs;
> +			task->thread.gcs_size = size;
> +			if (task == current)
> +				write_sysreg_s(task->thread.gcspr_el0,
> +					       SYS_GCSPR_EL0);
> +
> +		}
> +	}

Nitpick: use a single 'if' instead of nesting (unless subsequent patches
add more to the first block).

Otherwise it looks fine.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>