linux-kernel - RE: [RFC][PATCH 1/2] Fix event.c misaligned address error

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:   Thu, 12 Sep 2019 08:50:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Ian Rogers' <irogers@...gle.com>,
        Numfor Mbiziwo-Tiapo <nums@...gle.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        "Namhyung Kim" <namhyung@...nel.org>,
        Song Liu <songliubraving@...com>, "mbd@...com" <mbd@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: RE: [RFC][PATCH 1/2] Fix event.c misaligned address error

From: Ian Rogers
> Sent: 11 September 2019 10:09
> On Wed, Jul 24, 2019 at 3:50 PM Numfor Mbiziwo-Tiapo <nums@...gle.com> wrote:
> >
> > The ubsan (undefined behavior sanitizer) build of perf throws an
> > error when the synthesize "Synthesize cpu map" function from
> > perf test is run.
> >
> > This can be reproduced by running (from the tip directory):
> > make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined"
> >
> > (see cover letter for why perf may not build)
> >
> > then running: tools/perf/perf test 44 -v
> >
> > This bug occurs because the cpu_map_data__synthesize function in
> > event.c calls synthesize_mask, casting the 'data' variable
> > (of type cpu_map_data*) to a cpu_map_mask*. Since struct
> > cpu_map_data is 2 byte aligned and struct cpu_map_mask is 8 byte
> > aligned this causes memory alignment issues.
> >
> > This is fixed by adding 6 bytes of padding to the struct cpu_map_data,
> > however, this will break compatibility between perf data files - a file
> > written by an old perf wouldn't work with a perf with this patch due
> > to event data alignment changing.
> >
> > Comments?
> >
> > Not-Quite-Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
> > ---
> >  tools/perf/util/event.h | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
> > index eb95f3384958..82eaf06c2604 100644
> > --- a/tools/perf/util/event.h
> > +++ b/tools/perf/util/event.h
> > @@ -433,6 +433,7 @@ struct cpu_map_mask {
> >
> >  struct cpu_map_data {
> >         u16     type;
> > +       u8 pad[6];
> >         char    data[];
> >  };
> >
> > --
> > 2.22.0.657.g960e92d24f-goog
> >
> An idea here is that, if this breaks backward compatibility, we
> introduce an aligned variant and work to deprecate the unaligned
> variant. I will look into making a patch set.

Adding a pad[6] makes no difference.
You need to add aligened(8) to the structure itself as well.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)