linux-kernel - Re: [RFC][PATCH] x86: Verify access

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Fri, 20 Jan 2017 09:50:00 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Andy Lutomirski <luto@...capital.net>,
        David Smith <dsmith@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [RFC][PATCH] x86: Verify access_ok() context

On Fri, 20 Jan 2017, Peter Zijlstra wrote:

> On Wed, Jan 18, 2017 at 04:19:47PM -0800, Andy Lutomirski wrote:
> > ISTM even with pagefault_disable() in play, using access_ok() from,
> > say, interrupt context is dangerous unless you've first checked that
> > you're in a task.  But I guess that in_task() would still return
> > false, e.g. in perf.
> 
> The test was created exactly because perf was using access_ok()
> _wrongly_. See commit: ae31fe51a3cc ("perf/x86: Restore TASK_SIZE check
> on frame pointer").

If you validate a user space address against current outside the task
context, then what guarantees that this user space address belongs to
current? Nothing!

Sure, there are interrupts like breakpoints, etc. where we exactly know
that the address which we are looking at belongs to current, because the
code accesses soemthing which belongs exactly to that breakpoint. And in
these cases we need a check which is designed specifically for that case.

Thanks,

	tglx