linux-kernel - [PATCH 3/3] Fix insn.c misaligned address error

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Message-Id: <20190724184512.162887-4-nums@google.com>
Date:   Wed, 24 Jul 2019 11:45:12 -0700
From:   Numfor Mbiziwo-Tiapo <nums@...gle.com>
To:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, songliubraving@...com, mbd@...com
Cc:     linux-kernel@...r.kernel.org, irogers@...gle.com,
        eranian@...gle.com, Numfor Mbiziwo-Tiapo <nums@...gle.com>
Subject: [PATCH 3/3] Fix insn.c misaligned address error

The ubsan (undefined behavior sanitizer) version of perf throws an
error on the 'x86 instruction decoder - new instructions' function
of perf test.

To reproduce this run:
make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined"

then run: tools/perf/perf test 62 -v

The error occurs in the __get_next macro (line 34) where an int is
read from a potentially unaligned address. Using memcpy instead of
assignment from an unaligned pointer.

Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
---
 tools/perf/util/intel-pt-decoder/insn.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/intel-pt-decoder/insn.c b/tools/perf/util/intel-pt-decoder/insn.c
index ca983e2bea8b..de1944c60aa9 100644
--- a/tools/perf/util/intel-pt-decoder/insn.c
+++ b/tools/perf/util/intel-pt-decoder/insn.c
@@ -31,7 +31,8 @@
 	((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
 
 #define __get_next(t, insn)	\
-	({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); r; })
+	({ t r; memcpy(&r, insn->next_byte, sizeof(t)); \
+		insn->next_byte += sizeof(t); r; })
 
 #define __peek_nbyte_next(t, insn, n)	\
 	({ t r = *(t*)((insn)->next_byte + n); r; })
-- 
2.22.0.657.g960e92d24f-goog