linux-kernel - Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error

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Date:   Thu, 21 Mar 2019 10:23:16 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>,
        Joel Fernandes <joel@...lfernandes.org>,
        He Zhe <zhe.he@...driver.com>
Subject: Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error_entry

On Thu, Mar 21, 2019 at 6:55 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Looks to be an issue with the save_stack_trace_user() not checking if
> the address is canonical before reading it. I guess access_ok() doesn't
> check that.

access_ok() definitely does check for non-canonical.

But it only does so when USER_DS is in effect.

If you use KERNEL_DS, then you have to check the address yourself.

                    Linus