linux-kernel - Re: [PATCH 01/10] perf,x86: Fix event/group validation

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

Message-ID: <CABPqkBTFPRwHX8zKERYFrMBVQor5GJcDd4ZcKt8WL-tjbJdzLw@mail.gmail.com>
Date:	Thu, 21 May 2015 06:07:20 -0700
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Jiri Olsa <jolsa@...hat.com>,
	"Liang, Kan" <kan.liang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Hunter <ahh@...gle.com>,
	Maria Dimakopoulou <maria.n.dimakopoulou@...il.com>
Subject: Re: [PATCH 01/10] perf,x86: Fix event/group validation

On Thu, May 21, 2015 at 5:56 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, May 21, 2015 at 05:35:02AM -0700, Stephane Eranian wrote:
>> > Commit e979121b1b15 ("perf/x86/intel: Implement cross-HT corruption
>> > bug workaround") made the situation much worse by actually setting the
>> > event->hw.constraint value to NULL, so when validation and actual
>> > scheduling interact we get NULL ptr derefs.
>> >
>>
>> But  x86_schedule_events() does reset the hw.constraint for each invocation:
>>
>>            c = x86_pmu.get_event_constraints(cpuc, i, cpuc->event_list[i]);
>>            hwc->constraint = c;
>
> Yes, so if you have:
>
>         validate_group()
>
>                 hwc->constraint = c;
>
Ok, you get that because validate_group() invokes x6_schedule_events() but
on the fake_cpuc. This on fake_cpuc->event_list[]->hwc.

>         <context switch>
>
>                 c = hwc->constraint;
>
> The second c might not be the first.
And where does this assignment come from?
For actual scheduling, we are using the actual cpuc, not fake_cpuc.
Validate_group() does not modify global cpuc state. Or am I missing something?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/