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Date:   Mon, 18 Nov 2019 13:22:14 +0100
From:   Jiri Olsa <jolsa@redhat.com>
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] perf session: fix decompression of
 PERF_RECORD_COMPRESSED records
Message-ID: <20191118122214.GB14046@krava>
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On Mon, Nov 18, 2019 at 02:30:04PM +0300, Alexey Budankov wrote:
>=20
> Avoid termination of trace loading in case the last record in
> the decompressed buffer partly resides in the following
> mmaped PERF_RECORD_COMPRESSED record. In this case NULL value
> returned by fetch_mmaped_event() means to proceed to the next
> mmaped record then decompress it and load compressed events.
>=20
> The issue can be reproduced like this:
>=20
>   $ perf record -z -- some_long_running_workload
>   $ perf report --stdio -vv
>   decomp (B): 44519 to 163000
>   decomp (B): 48119 to 174800
>   decomp (B): 65527 to 131072
>   fetch_mmaped_event: head=3D0x1ffe0 event->header_size=3D0x28, mmap_size=
=3D0x20000: fuzzed perf.data?
>   Error:
>   failed to process sample
>   ...
>=20
> Testing:
> 71: Zstd perf.data compression/decompression              : Ok
>=20
> Fixes: 57fc032ad643 ("perf session: Avoid infinite loop when seeing inval=
id header.size")
> Link: https://marc.info/?l=3Dlinux-kernel&m=3D156580812427554&w=3D2
> Co-developed-by: Jiri Olsa <jolsa@kernel.org>
> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> ---
> Changes in v2:
> - avoided static declaration of prefetch_event();
> - renamed 'ret' to 'error' for returning in case of split compressed=20
>   or overlapping records;
> - passed only needs_swap quality into fetch_*_event() instead of=20
>   the whole session object;
> ---
>  tools/perf/util/session.c | 44 ++++++++++++++++++++++++---------------
>  1 file changed, 27 insertions(+), 17 deletions(-)
>=20
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index f07b8ecb91bc..c2b0703d6587 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1958,8 +1958,8 @@ static int __perf_session__process_pipe_events(stru=
ct perf_session *session)
>  }
> =20
>  static union perf_event *
> -fetch_mmaped_event(struct perf_session *session,
> -=09=09   u64 head, size_t mmap_size, char *buf)
> +prefetch_event(char *buf, u64 head, size_t mmap_size,
> +=09       bool needs_swap, union perf_event *error)
>  {
>  =09union perf_event *event;
> =20
> @@ -1971,20 +1971,32 @@ fetch_mmaped_event(struct perf_session *session,
>  =09=09return NULL;
> =20
>  =09event =3D (union perf_event *)(buf + head);
> +=09if (needs_swap)
> +=09=09perf_event_header__bswap(&event->header);
> =20
> -=09if (session->header.needs_swap)
> +=09if (head + event->header.size <=3D mmap_size)
> +=09=09return event;
> +
> +=09/* We're not fetching the event so swap back again */
> +=09if (needs_swap)
>  =09=09perf_event_header__bswap(&event->header);
> =20
> -=09if (head + event->header.size > mmap_size) {
> -=09=09/* We're not fetching the event so swap back again */
> -=09=09if (session->header.needs_swap)
> -=09=09=09perf_event_header__bswap(&event->header);
> -=09=09pr_debug("%s: head=3D%#" PRIx64 " event->header_size=3D%#x, mmap_s=
ize=3D%#zx: fuzzed perf.data?\n",
> -=09=09=09 __func__, head, event->header.size, mmap_size);
> -=09=09return ERR_PTR(-EINVAL);
> -=09}
> +=09pr_debug("%s: head=3D%#" PRIx64 " event->header_size=3D%#x, mmap_size=
=3D%#zx\n",
> +=09=09__func__, head, event->header.size, mmap_size);

you're missign the 'fuzzed perf.data?' in here

I think we should keep it just change to: 'fuzzed or compressed perf.data?'

thanks,
jirka