Re: [PATCH v10 21/40] arm64/gcs: Implement shadow stack prctl() interface

[Catalin Marinas <catalin.marinas@arm.com>]

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>