[PATCH v2 1/3] perf tools: Prevent out-of-bounds access to registers

[German Gomez]

The size of the cache of register values is arch-dependant
(PERF_REGS_MAX). This has the potential of causing an out-of-bounds
access in the function "perf_reg_value" if the local architecture
contains less registers than the one the perf.data file was recorded on.

Since the maximum number of registers is bound by the bitmask "u64
cache_mask", and the size of the cache when running under x86 systems is
64 already, fix the size to 64 and add a range-check to the function
"perf_reg_value" to prevent out-of-bounds access.

Reported-by: Alexandre Truong <alexandre.truong at arm.com>
Signed-off-by: German Gomez <german.gomez at arm.com>
---
 tools/perf/util/event.h     | 5 ++++-
 tools/perf/util/perf_regs.c | 3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index 95ffed663..c59331eea 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -44,13 +44,16 @@ struct perf_event_attr;
 /* perf sample has 16 bits size limit */
 #define PERF_SAMPLE_MAX_SIZE (1 << 16)
 
+/* number of register is bound by the number of bits in regs_dump::mask (64) */
+#define PERF_SAMPLE_REGS_CACHE_SIZE (8 * sizeof(u64))
+
 struct regs_dump {
 	u64 abi;
 	u64 mask;
 	u64 *regs;
 
 	/* Cached values/mask filled by first register access. */
-	u64 cache_regs[PERF_REGS_MAX];
+	u64 cache_regs[PERF_SAMPLE_REGS_CACHE_SIZE];
 	u64 cache_mask;
 };
 
diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c
index 5ee47ae15..06a7461ba 100644
--- a/tools/perf/util/perf_regs.c
+++ b/tools/perf/util/perf_regs.c
@@ -25,6 +25,9 @@ int perf_reg_value(u64 *valp, struct regs_dump *regs, int id)
 	int i, idx = 0;
 	u64 mask = regs->mask;
 
+	if ((u64)id >= PERF_SAMPLE_REGS_CACHE_SIZE)
+		return -EINVAL;
+
 	if (regs->cache_mask & (1ULL << id))
 		goto out;
 
-- 
2.25.1