linux-kernel - [tip: perf/urgent] perf/x86/intel/pt: Fix crash with stop filters in single-range mode

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Message-ID: <164389881167.16921.8753176904617913417.tip-bot2@tip-bot2>
Date:   Thu, 03 Feb 2022 14:33:31 -0000
From:   "tip-bot2 for Tristan Hume" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Tristan Hume <tristan@...me.ca>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Adrian Hunter <adrian.hunter@...el.com>, stable@...nel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: perf/urgent] perf/x86/intel/pt: Fix crash with stop filters in
 single-range mode

The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     1d9093457b243061a9bba23543c38726e864a643
Gitweb:        https://git.kernel.org/tip/1d9093457b243061a9bba23543c38726e864a643
Author:        Tristan Hume <tristan@...me.ca>
AuthorDate:    Thu, 27 Jan 2022 17:08:06 -05:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 02 Feb 2022 13:11:40 +01:00

perf/x86/intel/pt: Fix crash with stop filters in single-range mode

Add a check for !buf->single before calling pt_buffer_region_size in a
place where a missing check can cause a kernel crash.

Fixes a bug introduced by commit 670638477aed ("perf/x86/intel/pt:
Opportunistically use single range output mode"), which added a
support for PT single-range output mode. Since that commit if a PT
stop filter range is hit while tracing, the kernel will crash because
of a null pointer dereference in pt_handle_status due to calling
pt_buffer_region_size without a ToPA configured.

The commit which introduced single-range mode guarded almost all uses of
the ToPA buffer variables with checks of the buf->single variable, but
missed the case where tracing was stopped by the PT hardware, which
happens when execution hits a configured stop filter.

Tested that hitting a stop filter while PT recording successfully
records a trace with this patch but crashes without this patch.

Fixes: 670638477aed ("perf/x86/intel/pt: Opportunistically use single range output mode")
Signed-off-by: Tristan Hume <tristan@...me.ca>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Adrian Hunter <adrian.hunter@...el.com>
Cc: stable@...nel.org
Link: https://lkml.kernel.org/r/20220127220806.73664-1-tristan@thume.ca
---
 arch/x86/events/intel/pt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 7f406c1..2d33bba 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -897,8 +897,9 @@ static void pt_handle_status(struct pt *pt)
 		 * means we are already losing data; need to let the decoder
 		 * know.
 		 */
-		if (!intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries) ||
-		    buf->output_off == pt_buffer_region_size(buf)) {
+		if (!buf->single &&
+		    (!intel_pt_validate_hw_cap(PT_CAP_topa_multiple_entries) ||
+		     buf->output_off == pt_buffer_region_size(buf))) {
 			perf_aux_output_flag(&pt->handle,
 			                     PERF_AUX_FLAG_TRUNCATED);
 			advance++;