On Wed, Nov 29, 2023 at 4:15 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
> Bpf cpu=v4 support is introduced in [1] and Commit 4cd58e9af8b9
> ("bpf: Support new 32bit offset jmp instruction") added support for new
> 32bit offset jmp instruction. Unfortunately, in function
> bpf_adj_delta_to_off(), for new branch insn with 32bit offset, the offset
> (plus/minor a small delta) compares to 16-bit offset bound
> [S16_MIN, S16_MAX], which caused the following verification failure:
> $ ./test_progs-cpuv4 -t verif_scale_pyperf180
> ...
> insn 10 cannot be patched due to 16-bit range
> ...
> libbpf: failed to load object 'pyperf180.bpf.o'
> scale_test:FAIL:expect_success unexpected error: -12 (errno 12)
> #405 verif_scale_pyperf180:FAIL
>
> Note that due to recent llvm18 development, the patch [2] (already applied
> in bpf-next) needs to be applied to bpf tree for testing purpose.
>
> The fix is rather simple. For 32bit offset branch insn, the adjusted
> offset compares to [S32_MIN, S32_MAX] and then verification succeeded.
>
> [1] https://lore.kernel.org/all/20230728011143.3710005-1-yonghong.song@xxxxxxxxx
> [2] https://lore.kernel.org/bpf/20231110193644.3130906-1-yonghong.song@xxxxxxxxx
>
> Fixes: 4cd58e9af8b9 ("bpf: Support new 32bit offset jmp instruction")
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
> kernel/bpf/core.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index cd3afe57ece3..beff7e1d7fd0 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -371,14 +371,17 @@ static int bpf_adj_delta_to_imm(struct bpf_insn *insn, u32 pos, s32 end_old,
> static int bpf_adj_delta_to_off(struct bpf_insn *insn, u32 pos, s32 end_old,
> s32 end_new, s32 curr, const bool probe_pass)
> {
> - const s32 off_min = S16_MIN, off_max = S16_MAX;
> + s64 off_min = S16_MIN, off_max = S16_MAX;
> s32 delta = end_new - end_old;
> - s32 off;
> + s64 off;
>
> - if (insn->code == (BPF_JMP32 | BPF_JA))
> + if (insn->code == (BPF_JMP32 | BPF_JA)) {
> off = insn->imm;
> - else
> + off_min = S32_MIN;
> + off_max = S32_MAX;
> + } else {
nit: it would be more symmetrical and easier to follow if you set
S16_{MIN,MAX} in this branch, instead of using variable initialization
approach
> off = insn->off;
> + }
>
> if (curr < pos && curr + off + 1 >= end_old)
> off += delta;
> --
> 2.34.1
>
