perf cpumap: Fix alignment for masks in event encoding

A mask encoding of a cpu map is laid out as:

  u16 nr
  u16 long_size
  unsigned long mask[];

However, the mask may be 8-byte aligned meaning there is a 4-byte pad
after long_size. This means 32-bit and 64-bit builds see the mask as
being at different offsets. On top of this the structure is in the byte
data[] encoded as:

  u16 type
  char data[]

This means the mask's struct isn't the required 4 or 8 byte aligned, but
is offset by 2. Consequently the long reads and writes are causing
undefined behavior as the alignment is broken.

Fix the mask struct by creating explicit 32 and 64-bit variants, use a
union to avoid data[] and casts; the struct must be packed so the
layout matches the existing perf.data layout. Taking an address of a
member of a packed struct breaks alignment so pass the packed
perf_record_cpu_map_data to functions, so they can access variables with
the right alignment.

As the 64-bit version has 4 bytes of padding, optimizing writing to only
write the 32-bit version.

Committer notes:

Disable warnings about 'packed' that break the build in some arches like
riscv64, but just around that specific struct.

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Bayduraev <alexey.v.bayduraev@linux.intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Colin Ian King <colin.king@intel.com>
Cc: Dave Marchevsky <davemarchevsky@fb.com>
Cc: German Gomez <german.gomez@arm.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Kees Kook <keescook@chromium.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Riccardo Mancini <rickyman7@gmail.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20220614143353.1559597-5-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/include/perf/event.h

@@ -6,6 +6,7 @@
 #include <linux/types.h>
 #include <linux/limits.h>
 #include <linux/bpf.h>
+#include <linux/compiler.h>
 #include <sys/types.h> /* pid_t */
 
 #define event_contains(obj, mem) ((obj).header.size > offsetof(typeof(obj), mem))
@@ -153,22 +154,60 @@ enum {
 	PERF_CPU_MAP__MASK = 1,
 };
 
+/*
+ * Array encoding of a perf_cpu_map where nr is the number of entries in cpu[]
+ * and each entry is a value for a CPU in the map.
+ */
 struct cpu_map_entries {
 	__u16			 nr;
 	__u16			 cpu[];
 };
 
-struct perf_record_record_cpu_map {
+/* Bitmap encoding of a perf_cpu_map where bitmap entries are 32-bit. */
+struct perf_record_mask_cpu_map32 {
+	/* Number of mask values. */
 	__u16			 nr;
+	/* Constant 4. */
 	__u16			 long_size;
-	unsigned long		 mask[];
+	/* Bitmap data. */
+	__u32			 mask[];
 };
 
-struct perf_record_cpu_map_data {
+/* Bitmap encoding of a perf_cpu_map where bitmap entries are 64-bit. */
+struct perf_record_mask_cpu_map64 {
+	/* Number of mask values. */
+	__u16			 nr;
+	/* Constant 8. */
+	__u16			 long_size;
+	/* Legacy padding. */
+	char                     __pad[4];
+	/* Bitmap data. */
+	__u64			 mask[];
+};
+
+/*
+ * 'struct perf_record_cpu_map_data' is packed as unfortunately an earlier
+ * version had unaligned data and we wish to retain file format compatibility.
+ * -irogers
+ */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpacked"
+#pragma GCC diagnostic ignored "-Wattributes"
+
+struct __packed perf_record_cpu_map_data {
 	__u16			 type;
-	char			 data[];
+	union {
+		/* Used when type == PERF_CPU_MAP__CPUS. */
+		struct cpu_map_entries cpus_data;
+		/* Used when type == PERF_CPU_MAP__MASK and long_size == 4. */
+		struct perf_record_mask_cpu_map32 mask32_data;
+		/* Used when type == PERF_CPU_MAP__MASK and long_size == 8. */
+		struct perf_record_mask_cpu_map64 mask64_data;
+	};
 };
 
+#pragma GCC diagnostic pop
+
 struct perf_record_cpu_map {
 	struct perf_event_header	 header;
 	struct perf_record_cpu_map_data	 data;

tools/perf/tests/cpumap.c

@@ -17,21 +17,23 @@ static int process_event_mask(struct perf_tool *tool __maybe_unused,
 			 struct machine *machine __maybe_unused)
 {
 	struct perf_record_cpu_map *map_event = &event->cpu_map;
-	struct perf_record_record_cpu_map *mask;
 	struct perf_record_cpu_map_data *data;
 	struct perf_cpu_map *map;
 	int i;
+	unsigned int long_size;
 
 	data = &map_event->data;
 
 	TEST_ASSERT_VAL("wrong type", data->type == PERF_CPU_MAP__MASK);
 
-	mask = (struct perf_record_record_cpu_map *)data->data;
+	long_size = data->mask32_data.long_size;
 
-	TEST_ASSERT_VAL("wrong nr",   mask->nr == 1);
+	TEST_ASSERT_VAL("wrong long_size", long_size == 4 || long_size == 8);
+
+	TEST_ASSERT_VAL("wrong nr",   data->mask32_data.nr == 1);
 
 	for (i = 0; i < 20; i++) {
-		TEST_ASSERT_VAL("wrong cpu", test_bit(i, mask->mask));
+		TEST_ASSERT_VAL("wrong cpu", perf_record_cpu_map_data__test_bit(i, data));
 	}
 
 	map = cpu_map__new_data(data);
@@ -51,19 +53,16 @@ static int process_event_cpus(struct perf_tool *tool __maybe_unused,
 			 struct machine *machine __maybe_unused)
 {
 	struct perf_record_cpu_map *map_event = &event->cpu_map;
-	struct cpu_map_entries *cpus;
 	struct perf_record_cpu_map_data *data;
 	struct perf_cpu_map *map;
 
 	data = &map_event->data;
 
 	TEST_ASSERT_VAL("wrong type", data->type == PERF_CPU_MAP__CPUS);
 
-	cpus = (struct cpu_map_entries *)data->data;
-
-	TEST_ASSERT_VAL("wrong nr",   cpus->nr == 2);
-	TEST_ASSERT_VAL("wrong cpu",  cpus->cpu[0] == 1);
-	TEST_ASSERT_VAL("wrong cpu",  cpus->cpu[1] == 256);
+	TEST_ASSERT_VAL("wrong nr",   data->cpus_data.nr == 2);
+	TEST_ASSERT_VAL("wrong cpu",  data->cpus_data.cpu[0] == 1);
+	TEST_ASSERT_VAL("wrong cpu",  data->cpus_data.cpu[1] == 256);
 
 	map = cpu_map__new_data(data);
 	TEST_ASSERT_VAL("wrong nr",  perf_cpu_map__nr(map) == 2);

tools/perf/util/cpumap.c

@@ -22,54 +22,102 @@ static int max_node_num;
  */
 static int *cpunode_map;
 
-static struct perf_cpu_map *cpu_map__from_entries(struct cpu_map_entries *cpus)
+bool perf_record_cpu_map_data__test_bit(int i,
+					const struct perf_record_cpu_map_data *data)
+{
+	int bit_word32 = i / 32;
+	__u32 bit_mask32 = 1U << (i & 31);
+	int bit_word64 = i / 64;
+	__u64 bit_mask64 = ((__u64)1) << (i & 63);
+
+	return (data->mask32_data.long_size == 4)
+		? (bit_word32 < data->mask32_data.nr) &&
+		(data->mask32_data.mask[bit_word32] & bit_mask32) != 0
+		: (bit_word64 < data->mask64_data.nr) &&
+		(data->mask64_data.mask[bit_word64] & bit_mask64) != 0;
+}
+
+/* Read ith mask value from data into the given 64-bit sized bitmap */
+static void perf_record_cpu_map_data__read_one_mask(const struct perf_record_cpu_map_data *data,
+						    int i, unsigned long *bitmap)
+{
+#if __SIZEOF_LONG__ == 8
+	if (data->mask32_data.long_size == 4)
+		bitmap[0] = data->mask32_data.mask[i];
+	else
+		bitmap[0] = data->mask64_data.mask[i];
+#else
+	if (data->mask32_data.long_size == 4) {
+		bitmap[0] = data->mask32_data.mask[i];
+		bitmap[1] = 0;
+	} else {
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+		bitmap[0] = (unsigned long)(data->mask64_data.mask[i] >> 32);
+		bitmap[1] = (unsigned long)data->mask64_data.mask[i];
+#else
+		bitmap[0] = (unsigned long)data->mask64_data.mask[i];
+		bitmap[1] = (unsigned long)(data->mask64_data.mask[i] >> 32);
+#endif
+	}
+#endif
+}
+static struct perf_cpu_map *cpu_map__from_entries(const struct perf_record_cpu_map_data *data)
 {
 	struct perf_cpu_map *map;
 
-	map = perf_cpu_map__empty_new(cpus->nr);
+	map = perf_cpu_map__empty_new(data->cpus_data.nr);
 	if (map) {
 		unsigned i;
 
-		for (i = 0; i < cpus->nr; i++) {
+		for (i = 0; i < data->cpus_data.nr; i++) {
 			/*
 			 * Special treatment for -1, which is not real cpu number,
 			 * and we need to use (int) -1 to initialize map[i],
 			 * otherwise it would become 65535.
 			 */
-			if (cpus->cpu[i] == (u16) -1)
+			if (data->cpus_data.cpu[i] == (u16) -1)
 				map->map[i].cpu = -1;
 			else
-				map->map[i].cpu = (int) cpus->cpu[i];
+				map->map[i].cpu = (int) data->cpus_data.cpu[i];
 		}
 	}
 
 	return map;
 }
 
-static struct perf_cpu_map *cpu_map__from_mask(struct perf_record_record_cpu_map *mask)
+static struct perf_cpu_map *cpu_map__from_mask(const struct perf_record_cpu_map_data *data)
 {
+	DECLARE_BITMAP(local_copy, 64);
+	int weight = 0, mask_nr = data->mask32_data.nr;
 	struct perf_cpu_map *map;
-	int nr, nbits = mask->nr * mask->long_size * BITS_PER_BYTE;
 
-	nr = bitmap_weight(mask->mask, nbits);
+	for (int i = 0; i < mask_nr; i++) {
+		perf_record_cpu_map_data__read_one_mask(data, i, local_copy);
+		weight += bitmap_weight(local_copy, 64);
+	}
+
+	map = perf_cpu_map__empty_new(weight);
+	if (!map)
+		return NULL;
 
-	map = perf_cpu_map__empty_new(nr);
-	if (map) {
-		int cpu, i = 0;
+	for (int i = 0, j = 0; i < mask_nr; i++) {
+		int cpus_per_i = (i * data->mask32_data.long_size  * BITS_PER_BYTE);
+		int cpu;
 
-		for_each_set_bit(cpu, mask->mask, nbits)
-			map->map[i++].cpu = cpu;
+		perf_record_cpu_map_data__read_one_mask(data, i, local_copy);
+		for_each_set_bit(cpu, local_copy, 64)
+			map->map[j++].cpu = cpu + cpus_per_i;
 	}
 	return map;
 
 }
 
-struct perf_cpu_map *cpu_map__new_data(struct perf_record_cpu_map_data *data)
+struct perf_cpu_map *cpu_map__new_data(const struct perf_record_cpu_map_data *data)
 {
 	if (data->type == PERF_CPU_MAP__CPUS)
-		return cpu_map__from_entries((struct cpu_map_entries *)data->data);
+		return cpu_map__from_entries(data);
 	else
-		return cpu_map__from_mask((struct perf_record_record_cpu_map *)data->data);
+		return cpu_map__from_mask(data);
 }
 
 size_t cpu_map__fprintf(struct perf_cpu_map *map, FILE *fp)

tools/perf/util/cpumap.h

@@ -37,9 +37,11 @@ struct cpu_aggr_map {
 
 struct perf_record_cpu_map_data;
 
+bool perf_record_cpu_map_data__test_bit(int i, const struct perf_record_cpu_map_data *data);
+
 struct perf_cpu_map *perf_cpu_map__empty_new(int nr);
 
-struct perf_cpu_map *cpu_map__new_data(struct perf_record_cpu_map_data *data);
+struct perf_cpu_map *cpu_map__new_data(const struct perf_record_cpu_map_data *data);
 size_t cpu_map__snprint(struct perf_cpu_map *map, char *buf, size_t size);
 size_t cpu_map__snprint_mask(struct perf_cpu_map *map, char *buf, size_t size);
 size_t cpu_map__fprintf(struct perf_cpu_map *map, FILE *fp);

tools/perf/util/session.c

@@ -916,30 +916,30 @@ static void perf_event__cpu_map_swap(union perf_event *event,
 				     bool sample_id_all __maybe_unused)
 {
 	struct perf_record_cpu_map_data *data = &event->cpu_map.data;
-	struct cpu_map_entries *cpus;
-	struct perf_record_record_cpu_map *mask;
-	unsigned i;
 
 	data->type = bswap_16(data->type);
 
 	switch (data->type) {
 	case PERF_CPU_MAP__CPUS:
-		cpus = (struct cpu_map_entries *)data->data;
-
-		cpus->nr = bswap_16(cpus->nr);
+		data->cpus_data.nr = bswap_16(data->cpus_data.nr);
 
-		for (i = 0; i < cpus->nr; i++)
-			cpus->cpu[i] = bswap_16(cpus->cpu[i]);
+		for (unsigned i = 0; i < data->cpus_data.nr; i++)
+			data->cpus_data.cpu[i] = bswap_16(data->cpus_data.cpu[i]);
 		break;
 	case PERF_CPU_MAP__MASK:
-		mask = (struct perf_record_record_cpu_map *)data->data;
-
-		mask->nr = bswap_16(mask->nr);
-		mask->long_size = bswap_16(mask->long_size);
+		data->mask32_data.long_size = bswap_16(data->mask32_data.long_size);
 
-		switch (mask->long_size) {
-		case 4: mem_bswap_32(&mask->mask, mask->nr); break;
-		case 8: mem_bswap_64(&mask->mask, mask->nr); break;
+		switch (data->mask32_data.long_size) {
+		case 4:
+			data->mask32_data.nr = bswap_16(data->mask32_data.nr);
+			for (unsigned i = 0; i < data->mask32_data.nr; i++)
+				data->mask32_data.mask[i] = bswap_32(data->mask32_data.mask[i]);
+			break;
+		case 8:
+			data->mask64_data.nr = bswap_16(data->mask64_data.nr);
+			for (unsigned i = 0; i < data->mask64_data.nr; i++)
+				data->mask64_data.mask[i] = bswap_64(data->mask64_data.mask[i]);
+			break;
 		default:
 			pr_err("cpu_map swap: unsupported long size\n");
 		}

tools/perf/util/synthetic-events.c

@@ -1184,27 +1184,33 @@ int perf_event__synthesize_thread_map2(struct perf_tool *tool,
 	return err;
 }
 
-static void synthesize_cpus(struct cpu_map_entries *cpus,
+static void synthesize_cpus(struct perf_record_cpu_map_data *data,
 			    const struct perf_cpu_map *map)
 {
 	int i, map_nr = perf_cpu_map__nr(map);
 
-	cpus->nr = map_nr;
+	data->cpus_data.nr = map_nr;
 
 	for (i = 0; i < map_nr; i++)
-		cpus->cpu[i] = perf_cpu_map__cpu(map, i).cpu;
+		data->cpus_data.cpu[i] = perf_cpu_map__cpu(map, i).cpu;
 }
 
-static void synthesize_mask(struct perf_record_record_cpu_map *mask,
+static void synthesize_mask(struct perf_record_cpu_map_data *data,
 			    const struct perf_cpu_map *map, int max)
 {
-	int i;
+	int idx;
+	struct perf_cpu cpu;
+
+	/* Due to padding, the 4bytes per entry mask variant is always smaller. */
+	data->mask32_data.nr = BITS_TO_U32(max);
+	data->mask32_data.long_size = 4;
 
-	mask->nr = BITS_TO_LONGS(max);
-	mask->long_size = sizeof(long);
+	perf_cpu_map__for_each_cpu(cpu, idx, map) {
+		int bit_word = cpu.cpu / 32;
+		__u32 bit_mask = 1U << (cpu.cpu & 31);
 
-	for (i = 0; i < perf_cpu_map__nr(map); i++)
-		set_bit(perf_cpu_map__cpu(map, i).cpu, mask->mask);
+		data->mask32_data.mask[bit_word] |= bit_mask;
+	}
 }
 
 static size_t cpus_size(const struct perf_cpu_map *map)
@@ -1215,7 +1221,7 @@ static size_t cpus_size(const struct perf_cpu_map *map)
 static size_t mask_size(const struct perf_cpu_map *map, int *max)
 {
 	*max = perf_cpu_map__max(map).cpu;
-	return sizeof(struct perf_record_record_cpu_map) + BITS_TO_LONGS(*max) * sizeof(long);
+	return sizeof(struct perf_record_mask_cpu_map32) + BITS_TO_U32(*max) * sizeof(__u32);
 }
 
 static void *cpu_map_data__alloc(const struct perf_cpu_map *map, size_t *size,
@@ -1248,7 +1254,7 @@ static void *cpu_map_data__alloc(const struct perf_cpu_map *map, size_t *size,
 		*type  = PERF_CPU_MAP__MASK;
 	}
 
-	*size += sizeof(struct perf_record_cpu_map_data);
+	*size += sizeof(__u16); /* For perf_record_cpu_map_data.type. */
 	*size = PERF_ALIGN(*size, sizeof(u64));
 	return zalloc(*size);
 }
@@ -1261,18 +1267,18 @@ static void cpu_map_data__synthesize(struct perf_record_cpu_map_data *data,
 
 	switch (type) {
 	case PERF_CPU_MAP__CPUS:
-		synthesize_cpus((struct cpu_map_entries *) data->data, map);
+		synthesize_cpus(data, map);
 		break;
 	case PERF_CPU_MAP__MASK:
-		synthesize_mask((struct perf_record_record_cpu_map *)data->data, map, max);
+		synthesize_mask(data, map, max);
 	default:
 		break;
 	}
 }
 
 static struct perf_record_cpu_map *cpu_map_event__new(const struct perf_cpu_map *map)
 {
-	size_t size = sizeof(struct perf_record_cpu_map);
+	size_t size = sizeof(struct perf_event_header);
 	struct perf_record_cpu_map *event;
 	int max;
 	u16 type;