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

[Andrii Nakryiko]

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

typo: rounding

>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---

Makes sense.

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>


>  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
>