Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752347Ab3CUSRp (ORCPT ); Thu, 21 Mar 2013 14:17:45 -0400 Received: from terminus.zytor.com ([198.137.202.10]:33609 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751484Ab3CUSRn (ORCPT ); Thu, 21 Mar 2013 14:17:43 -0400 Date: Thu, 21 Mar 2013 11:16:29 -0700 From: tip-bot for Stephane Eranian Message-ID: Cc: linux-kernel@vger.kernel.org, eranian@google.com, hpa@zytor.com, mingo@kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, eranian@google.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de In-Reply-To: <20130318133327.GA3056@quad> References: <20130318133327.GA3056@quad> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/urgent] perf: Fix ring_buffer perf_output_space() boundary calculation Git-Commit-ID: dd9c086d9f507d02d5ba4d7c5eef4bb9518088b8 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.7 (terminus.zytor.com [127.0.0.1]); Thu, 21 Mar 2013 11:16:35 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3648 Lines: 106 Commit-ID: dd9c086d9f507d02d5ba4d7c5eef4bb9518088b8 Gitweb: http://git.kernel.org/tip/dd9c086d9f507d02d5ba4d7c5eef4bb9518088b8 Author: Stephane Eranian AuthorDate: Mon, 18 Mar 2013 14:33:28 +0100 Committer: Ingo Molnar CommitDate: Thu, 21 Mar 2013 12:04:35 +0100 perf: Fix ring_buffer perf_output_space() boundary calculation This patch fixes a flaw in perf_output_space(). In case the size of the space needed is bigger than the actual buffer size, there may be situations where the function would return true (i.e., there is space) when it should not. head > offset due to rounding of the masking logic. The problem can be tested by activating BTS on Intel processors. A BTS record can be as big as 16 pages. The following command fails: $ perf record -m 4 -c 1 -e branches:u my_test_program You will get a buffer corruption with this. Perf report won't be able to parse the perf.data. The fix is to first check that the requested space is smaller than the buffer size. If so, then the masking logic will work fine. If not, then there is no chance the record can be saved and it will be gracefully handled by upper code layers. [ In v2, we also make the logic for the writable more explicit by renaming it to rb->overwrite because it tells whether or not the buffer can overwrite its tail (suggested by PeterZ). ] Signed-off-by: Stephane Eranian Acked-by: Peter Zijlstra Cc: peterz@infradead.org Cc: jolsa@redhat.com Cc: fweisbec@gmail.com Link: http://lkml.kernel.org/r/20130318133327.GA3056@quad Signed-off-by: Ingo Molnar --- kernel/events/internal.h | 2 +- kernel/events/ring_buffer.c | 22 ++++++++++++++++++---- 2 files changed, 19 insertions(+), 5 deletions(-) diff --git a/kernel/events/internal.h b/kernel/events/internal.h index d56a64c..eb675c4 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -16,7 +16,7 @@ struct ring_buffer { int page_order; /* allocation order */ #endif int nr_pages; /* nr of data pages */ - int writable; /* are we writable */ + int overwrite; /* can overwrite itself */ atomic_t poll; /* POLL_ for wakeups */ diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 23cb34f..97fddb0 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -18,12 +18,24 @@ static bool perf_output_space(struct ring_buffer *rb, unsigned long tail, unsigned long offset, unsigned long head) { - unsigned long mask; + unsigned long sz = perf_data_size(rb); + unsigned long mask = sz - 1; - if (!rb->writable) + /* + * check if user-writable + * overwrite : over-write its own tail + * !overwrite: buffer possibly drops events. + */ + if (rb->overwrite) return true; - mask = perf_data_size(rb) - 1; + /* + * verify that payload is not bigger than buffer + * otherwise masking logic may fail to detect + * the "not enough space" condition + */ + if ((head - offset) > sz) + return false; offset = (offset - tail) & mask; head = (head - tail) & mask; @@ -212,7 +224,9 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) rb->watermark = max_size / 2; if (flags & RING_BUFFER_WRITABLE) - rb->writable = 1; + rb->overwrite = 0; + else + rb->overwrite = 1; atomic_set(&rb->refcount, 1); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/