On Sun, 2023-07-16 at 22:51 +0100, Mark Brown wrote:
> +int arch_set_shadow_stack_status(struct task_struct *task, unsigned
> long arg)
> +{
> + unsigned long gcs, size;
> +
> + 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;
> +
> + /* If the task has been locked block any attempted changes */
> + if (task->thread.gcs_el0_mode & PR_SHADOW_STACK_LOCK)
> + return -EBUSY;
> +
> + /* Drop flags other than lock if disabling */
> + if (!(arg & PR_SHADOW_STACK_ENABLE))
> + arg &= ~PR_SHADOW_STACK_LOCK;
> +
> + /* 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;
> +
> + size = gcs_size(0);
> + gcs = alloc_gcs(task->thread.gcspr_el0, size,
> + 0, 0);
> + 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);
> +
> + }
> + }
> +
> + task->thread.gcs_el0_mode = arg;
> + if (task == current)
> + gcs_set_el0_mode(task);
> +
Ah! So does this task == current part mean this can be called from
another task via ptrace?
If so, then is the alloc_gcs() part on the wrong mm?
