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

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Date:   Tue, 21 Mar 2023 16:41:37 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-doc@...r.kernel.org, oleg@...hat.com, avagin@...il.com,
        peterz@...radead.org, luto@...nel.org, krisman@...labora.com,
        corbet@....net, shuah@...nel.org,
        Gregory Price <gregory.price@...verge.com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v13 1/3] syscall_user_dispatch: helper function to
 operate on given task

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