On 11/29/23 7:19 PM, Andrii Nakryiko wrote:
On Wed, Nov 29, 2023 at 4:15 PM Yonghong Song <yonghong.song@xxxxxxxxx> 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 | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index cd3afe57ece3..beff7e1d7fd0 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; + s64 off_min = S16_MIN, off_max = S16_MAX; s32 delta = end_new - end_old; - s32 off; + s64 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 {nit: it would be more symmetrical and easier to follow if you set S16_{MIN,MAX} in this branch, instead of using variable initialization approach
I tried to minimize the code change but probably not worth it. If no further errors in this patch, should I send v3 with better coding style or Maintainers could help do the change? Either way, please let me know.
off = insn->off; + } if (curr < pos && curr + off + 1 >= end_old) off += delta; -- 2.34.1
