bpf: Fix a verifier bug due to incorrect branch offset comparison wit…

…h cpu=v4

[ Upstream commit dfce9cb ]

Bpf cpu=v4 support is introduced in [1] and Commit 4cd58e9
("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: 4cd58e9 ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>

kernel/bpf/core.c

@@ -371,14 +371,18 @@ 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, off_max, off;
  s32 delta = end_new - end_old;
- s32 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 {
  off = insn->off;
+ off_min = S16_MIN;
+ off_max = S16_MAX;
+ }
 
  if (curr < pos && curr + off + 1 >= end_old)
  off += delta;