bpf: Fix a verifier bug due to incorrect branch offset comparison with cpu=v4
authorYonghong Song <yonghong.song@linux.dev>
Fri, 1 Dec 2023 02:46:40 +0000 (18:46 -0800)
committerAndrii Nakryiko <andrii@kernel.org>
Fri, 1 Dec 2023 23:41:50 +0000 (15:41 -0800)
commitdfce9cb3140592b886838e06f3e0c25fea2a9cae
treee3e3996806c2f48fb223715059d780f66af89db6
parent830139e7b6911266a84a77e1f18abf758995cc89
bpf: Fix a verifier bug due to incorrect branch offset comparison with cpu=v4

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@linux.dev
  [2] https://lore.kernel.org/bpf/20231110193644.3130906-1-yonghong.song@linux.dev

Fixes: 4cd58e9af8b9 ("bpf: Support new 32bit offset jmp instruction")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20231201024640.3417057-1-yonghong.song@linux.dev
kernel/bpf/core.c