Re: [PATCH v13 1/3] syscall_user_dispatch: helper function to operate on given task

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

Gregory!

On Wed, Mar 01 2023 at 15:58, Gregory Price wrote:
> +static int task_set_syscall_user_dispatch(struct task_struct *task, unsigned long mode,
> +					  unsigned long offset, unsigned long len,
> +					  char __user *selector)
>  {
>  	switch (mode) {
>  	case PR_SYS_DISPATCH_OFF:
        ...

	case PR_SYS_DISPATCH_ON:
		if (selector && !access_ok(selector, sizeof(*selector)))
			return -EFAULT;

I'm not seing how this can work on ARM64 when user pointer tagging is
enabled in the tracee, but not in the tracer. In such a case, if the
pointer is tagged, access_ok() will fail because access_ok() wont untag
it.

Thanks,

        tglx