bpf: Fix a verifier bug due to incorrect branch offset comparison with cpu=v4

[ Upstream commit dfce9cb3140592b886838e06f3e0c25fea2a9cae ]

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
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 64fcd81..5d1efe5 100644 (file)
--- a/kernel/bpf/core.c
+++ b/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;