This is a note to let you know that I've just added the patch titled
bpf: Fix a verifier bug due to incorrect branch offset comparison with cpu=v4
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-fix-a-verifier-bug-due-to-incorrect-branch-offset-comparison-with-cpu-v4.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From dfce9cb3140592b886838e06f3e0c25fea2a9cae Mon Sep 17 00:00:00 2001
From: Yonghong Song <yonghong.song@xxxxxxxxx>
Date: Thu, 30 Nov 2023 18:46:40 -0800
Subject: bpf: Fix a verifier bug due to incorrect branch offset comparison with cpu=v4
From: Yonghong Song <yonghong.song@xxxxxxxxx>
commit dfce9cb3140592b886838e06f3e0c25fea2a9cae upstream.
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>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20231201024640.3417057-1-yonghong.song@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/bpf/core.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -365,14 +365,18 @@ static int bpf_adj_delta_to_imm(struct b
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;
Patches currently in stable-queue which might be from yonghong.song@xxxxxxxxx are
queue-6.1/bpf-fix-a-verifier-bug-due-to-incorrect-branch-offset-comparison-with-cpu-v4.patch
queue-6.1/bpf-support-new-32bit-offset-jmp-instruction.patch
