On 11/29/23 8:54 AM, Yonghong Song 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 | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index cd3afe57ece3..74f2fd48148c 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;
+ s32 off_min = S16_MIN, off_max = S16_MAX;
s32 delta = end_new - end_old;
s32 off;
These should all be converted to s64, no? E.g. further below
the test will never trigger then for jmp32:
if (off < off_min || off > off_max)
return -ERANGE;
- 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;
+ }
if (curr < pos && curr + off + 1 >= end_old)
off += delta;
