From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BBD3EC433EF for ; Thu, 31 Mar 2022 14:20:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237468AbiCaOVz (ORCPT ); Thu, 31 Mar 2022 10:21:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237487AbiCaOVv (ORCPT ); Thu, 31 Mar 2022 10:21:51 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id BD62F1BE4D3; Thu, 31 Mar 2022 07:20:03 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4B5C81576; Thu, 31 Mar 2022 07:20:03 -0700 (PDT) Received: from [10.57.8.37] (unknown [10.57.8.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 256FC3F73B; Thu, 31 Mar 2022 07:20:02 -0700 (PDT) Message-ID: <77fa14e8-6630-c0e9-21fc-2603f7383f5f@arm.com> Date: Thu, 31 Mar 2022 15:20:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH] perf session: Remap buf if there is no space for event Content-Language: en-US To: Denis Nikitin , acme@kernel.org, linux-perf-users@vger.kernel.org Cc: jolsa@kernel.org, alexey.budankov@linux.intel.com, alexander.shishkin@linux.intel.com, namhyung@kernel.org, linux-kernel@vger.kernel.org References: <20220330031130.2152327-1-denik@chromium.org> From: James Clark In-Reply-To: <20220330031130.2152327-1-denik@chromium.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/03/2022 04:11, Denis Nikitin wrote: > If a perf event doesn't fit into remaining buffer space return NULL to > remap buf and fetch the event again. > Keep the logic to error out on inadequate input from fuzzing. > > This fixes perf failing on ChromeOS (with 32b userspace): > > $ perf report -v -i perf.data > ... > prefetch_event: head=0x1fffff8 event->header_size=0x30, mmap_size=0x2000000: fuzzed or compressed perf.data? > Error: > failed to process sample > > Fixes: 57fc032ad643 ("perf session: Avoid infinite loop when seeing invalid header.size") > Signed-off-by: Denis Nikitin > --- > tools/perf/util/session.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c > index 3b8dfe603e50..45a30040ec8d 100644 > --- a/tools/perf/util/session.c > +++ b/tools/perf/util/session.c > @@ -2095,6 +2095,7 @@ prefetch_event(char *buf, u64 head, size_t mmap_size, > bool needs_swap, union perf_event *error) > { > union perf_event *event; > + u16 event_size; > > /* > * Ensure we have enough space remaining to read > @@ -2107,15 +2108,23 @@ prefetch_event(char *buf, u64 head, size_t mmap_size, > if (needs_swap) > perf_event_header__bswap(&event->header); > > - if (head + event->header.size <= mmap_size) > + event_size = event->header.size; > + if (head + event_size <= mmap_size) > return event; > > /* We're not fetching the event so swap back again */ > if (needs_swap) > perf_event_header__bswap(&event->header); > > - pr_debug("%s: head=%#" PRIx64 " event->header_size=%#x, mmap_size=%#zx:" > - " fuzzed or compressed perf.data?\n",__func__, head, event->header.size, mmap_size); > + /* Check if the event fits into the next mmapped buf. */ > + if (event_size <= mmap_size - head % page_size) { > + /* Remap buf and fetch again. */ > + return NULL; Hi Denis, I tested this and it does fix the issue with a 32bit build. One concern is that the calculation to see if it will fit in the next map is dependent on the implementation of reader__mmap(). I think it would be possible for that to change slightly and then you could still get an infinite loop. But I can't really see a better way to do it, and it's unlikely for reader__mmap() to be modified to map data in a way to waste part of the buffer so it's probably fine. Maybe you could extract a function to calculate where the new offset would be in the buffer and share it between here and reader__mmap(). That would also make it more obvious what the 'head % page_size' bit is for. Either way: Reviewed-by: James Clark > + } > + > + /* Invalid input. Event size should never exceed mmap_size. */ > + pr_debug("%s: head=%#" PRIx64 " event->header.size=%#x, mmap_size=%#zx:" > + " fuzzed or compressed perf.data?\n", __func__, head, event_size, mmap_size); > > return error; > }