Re: [PATCH] perf bpf: 8 byte align bpil data

Ian Rogers
2022-06-27T17:18:11Z

On Mon, Jun 13, 2022 at 6:47 PM Ian Rogers <irogers@google.com> wrote:
>
> 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.

Happy Monday, polite ping!

Thanks,
Ian

> 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
>