linux-kernel - Re: [PATCH] perf/core: generate overflow signal when samples are dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we entered the kernel in the "skid" region)

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: <20170628174900.GG8252@leverpostej>
Date:   Wed, 28 Jun 2017 18:49:01 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Kyle Huey <me@...ehuey.com>,
        Vince Weaver <vincent.weaver@...ne.edu>
Cc:     "Jin, Yao" <yao.jin@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        stable@...r.kernel.org,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, acme@...nel.org,
        jolsa@...nel.org, kan.liang@...el.com,
        Will Deacon <will.deacon@....com>, gregkh@...uxfoundation.org,
        Robert O'Callahan <robert@...llahan.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf/core: generate overflow signal when samples are
 dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we
 entered the kernel in the "skid" region)

On Wed, Jun 28, 2017 at 09:48:27AM -0700, Kyle Huey wrote:
> On Wed, Jun 28, 2017 at 3:56 AM, Mark Rutland <mark.rutland@....com> wrote:
> > @@ -6101,6 +6116,12 @@ void perf_prepare_sample(struct perf_event_header *header,
> >         struct perf_output_handle handle;
> >         struct perf_event_header header;
> >
> > +       /*
> > +        * For security, drop the skid kernel samples if necessary.
> > +        */
> > +       if (!sample_is_allowed(event, regs))
> > +               return ret;
> 
> Just a bare return here.

Ugh, yes. Sorry about that. I'll fix that up.

[...]

> I can confirm that with that fixed to compile, this patch fixes rr.

Thanks for giving this a go.

Having thought about this some more, I think Vince does make a good
point that throwing away samples is liable to break stuff, e.g. that
which only relies on (non-sensitive) samples.

It still seems wrong to make up data, though.

Maybe for exclude_kernel && !exclude_user events we can always generate
samples from the user regs, rather than the exception regs. That's going
to be closer to what the user wants, regardless. I'll take a look
tomorrow.

Thanks,
Mark.