[PATCH] perf bpf: 8 byte align bpil data

Ian Rogers
2022-06-14T01:47:39Z

bpil data is accessed assuming 64-bit alignment resulting in undefined
behavior as the data is just byte aligned. With an -fsanitize=undefined
build the following errors are observed:

$ sudo perf record -a sleep 1
util/bpf-event.c:310:22: runtime error: load of misaligned address 0x55f61084520f for type '__u64', which requires 8 byte alignment
0x55f61084520f: note: pointer points here
a8 fe ff ff 3c 51 d3 c0 ff ff ff ff 04 84 d3 c0 ff ff ff ff d8 aa d3 c0 ff ff ff ff a4 c0 d3 c0
^
util/bpf-event.c:311:20: runtime error: load of misaligned address 0x55f61084522f for type '__u32', which requires 4 byte alignment
0x55f61084522f: note: pointer points here
ff ff ff ff c7 17 00 00 f1 02 00 00 1f 04 00 00 58 04 00 00 00 00 00 00 0f 00 00 00 63 02 00 00
^
util/bpf-event.c:198:33: runtime error: member access within misaligned address 0x55f61084523f for type 'const struct bpf_func_info', which requires 4 byte alignment
0x55f61084523f: note: pointer points here
58 04 00 00 00 00 00 00 0f 00 00 00 63 02 00 00 3b 00 00 00 ab 02 00 00 44 00 00 00 14 03 00 00

Correct this by rouding up the data sizes and aligning the pointers.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/bpf-utils.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/bpf-utils.c b/tools/perf/util/bpf-utils.c
index e271e05e51bc..80b1d2b3729b 100644
--- a/tools/perf/util/bpf-utils.c
+++ b/tools/perf/util/bpf-utils.c
@@ -149,11 +149,10 @@ get_bpf_prog_info_linear(int fd, __u64 arrays)
count = bpf_prog_info_read_offset_u32(&info, desc->count_offset);
size = bpf_prog_info_read_offset_u32(&info, desc->size_offset);

- data_len += count * size;
+ data_len += roundup(count * size, sizeof(__u64));
}

/* step 3: allocate continuous memory */
- data_len = roundup(data_len, sizeof(__u64));
info_linear = malloc(sizeof(struct perf_bpil) + data_len);
if (!info_linear)
return ERR_PTR(-ENOMEM);
@@ -180,7 +179,7 @@ get_bpf_prog_info_linear(int fd, __u64 arrays)
bpf_prog_info_set_offset_u64(&info_linear->info,
desc->array_offset,
ptr_to_u64(ptr));
- ptr += count * size;
+ ptr += roundup(count * size, sizeof(__u64));
}

/* step 5: call syscall again to get required arrays */
--
2.36.1.476.g0c4daa206d-goog