From:   Thomas Gleixner <tglx@linutronix.de>
To:     Gregory Price <gourry.memverge@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     linux-doc@vger.kernel.org, oleg@redhat.com, avagin@gmail.com,
        peterz@infradead.org, luto@kernel.org, krisman@collabora.com,
        corbet@lwn.net, shuah@kernel.org,
        Gregory Price <gregory.price@memverge.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [PATCH v13 1/3] syscall_user_dispatch: helper function to
 operate on given task
In-Reply-To: <20230301205843.2164-2-gregory.price@memverge.com>
References: <20230301205843.2164-1-gregory.price@memverge.com>
 <20230301205843.2164-2-gregory.price@memverge.com>
Date:   Tue, 21 Mar 2023 16:41:37 +0100
Message-ID: <87cz529kni.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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