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>