Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190320221534.165ab87b@oasis.local.home> <20190321083317.GL6058@hirez.programming.kicks-ass.net>
 <20190321090241.GL6521@hirez.programming.kicks-ass.net> <20190321104517.GM6521@hirez.programming.kicks-ass.net>
 <20190321093242.4a948198@gandalf.local.home> <20190321095502.47b51356@gandalf.local.home>
In-Reply-To: <20190321095502.47b51356@gandalf.local.home>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 21 Mar 2019 10:23:16 -0700
Message-ID: <CAHk-=whvxJjBBOmQSsrB-xHkc6xm8zGHsBRgpxh14UsEY_g+nw@mail.gmail.com>
Subject: Re: [RFC][PATCH] tracing/x86: Save CR2 before tracing irqsoff on error_entry
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@amacapital.net>,
        Joel Fernandes <joel@joelfernandes.org>,
        He Zhe <zhe.he@windriver.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Mar 21, 2019 at 6:55 AM Steven Rostedt <rostedt@goodmis.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