From: Yonghong Song <yonghong.song@linux.dev>
To: Eduard Zingerman <eddyz87@gmail.com>, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
kernel-team@fb.com
Subject: Re: [PATCH bpf-next v5 08/21] bpf: Walk the exception unwind in the verifier
Date: Wed, 23 Sep 2026 11:01:10 -0700 [thread overview]
Message-ID: <6ade3aa7-a77e-4a69-81d7-4514a35bc4d3@linux.dev> (raw)
In-Reply-To: <2333883f3fe2abcc40679edb4dc11f7b9bf5d1dd.camel@gmail.com>
On 9/23/26 9:34 AM, Eduard Zingerman wrote:
> On Tue, 2026-09-22 at 21:59 -0700, Yonghong Song wrote:
>
> ...
>
>> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
>> index e12ec91b8150..3146f707e030 100644
>> --- a/include/linux/bpf_verifier.h
>> +++ b/include/linux/bpf_verifier.h
>> @@ -429,7 +429,8 @@ struct bpf_jmp_history_entry {
>> u32 prev_idx : 20;
>> /* special INSN_F_xxx flags */
>> u32 flags : 4;
>> - u32 : 8;
>> + u32 unwind_frames : 4; /* frames popped to reach this landing pad */
>> + u32 : 4;
>> /*
>> * additional registers that need precision tracking when this
>> * jump is backtracked, vector of five 11-bit records
>> @@ -510,6 +511,9 @@ struct bpf_verifier_state {
>> bool speculative;
>> bool in_sleepable;
>>
>> + bool unwinding; /* an exception is in flight */
>> + u8 unwind_frameno; /* the frame whose landing pad is running */
>> +
>> /* first and last insn idx of this verifier state */
>> u32 first_insn_idx;
>> u32 last_insn_idx;
>> @@ -991,6 +995,8 @@ struct bpf_verifier_env {
>> } cfg;
>> struct backtrack_state bt;
>> struct bpf_jmp_history_entry *cur_hist_ent;
>> + u8 cur_unwind_frames; /* frames popped to reach this insn, if a pad */
>> + u8 unwind_frames; /* frames popped, staged for the next insn */
> Similarly to v4, stashing these variables into env in one place and
> reading them in another in order to push to jump history is an
> obfuscation step. Why don't you want to push to the jump history right
> away? Like in [1].
>
> So far the only field in env that changes with current verifier state is insn_idx.
> I don't see why this feature requires adding two more such fields.
>
> [1] https://github.com/kernel-patches/bpf/commit/fbc89e90cacd207b4271da25ed7a380f6b56125e#diff-edbb57adf10d1ce1fbb830a34fa92712fd01db1fbd9b6f2504001eb7bcc7b9d0R5604-R18577
> (with corresponding changes in backtrack.c in the same commit)
Okay, I looked at your backtrack.c and verifier.c related code.
I will use jump history then.
>
> ...
next prev parent reply other threads:[~2026-09-23 18:01 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-23 4:58 [PATCH bpf-next v5 00/21] bpf: Run exception cleanup landing pads when bpf_throw() unwinds Yonghong Song
2026-09-23 4:58 ` [PATCH bpf-next v5 01/21] bpf: Pack bpf_insn_aux_data flags into bit fields Yonghong Song
2026-09-23 5:40 ` bot+bpf-ci
2026-09-23 19:16 ` Eduard Zingerman
2026-09-23 4:58 ` [PATCH bpf-next v5 02/21] bpf: Accept the compiler's exception cleanup table at program load Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 03/21] bpf: Add the bpf_unwind_resume() kfunc Yonghong Song
2026-09-23 6:13 ` Kumar Kartikeya Dwivedi
2026-09-23 4:59 ` [PATCH bpf-next v5 04/21] bpf: Add lookups for exception cleanup resumes and landing pads Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 05/21] bpf: Prepare for an exception cleanup table before the CFG walk Yonghong Song
2026-09-23 5:40 ` bot+bpf-ci
2026-09-23 4:59 ` [PATCH bpf-next v5 06/21] bpf: Make exception landing pads reachable in the CFG Yonghong Song
2026-09-23 5:51 ` bot+bpf-ci
2026-09-23 19:25 ` Eduard Zingerman
2026-09-23 4:59 ` [PATCH bpf-next v5 07/21] bpf: Explore the landing pads no call site reaches Yonghong Song
2026-09-23 16:26 ` Eduard Zingerman
2026-09-23 17:27 ` Yonghong Song
2026-09-23 18:06 ` Eduard Zingerman
2026-09-23 18:09 ` Yonghong Song
2026-09-23 21:28 ` Alexei Starovoitov
2026-09-23 22:19 ` Eduard Zingerman
2026-09-23 23:20 ` Alexei Starovoitov
2026-09-24 0:13 ` Kumar Kartikeya Dwivedi
2026-09-24 1:53 ` Alexei Starovoitov
2026-09-24 6:12 ` Kumar Kartikeya Dwivedi
2026-09-23 23:09 ` Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 08/21] bpf: Walk the exception unwind in the verifier Yonghong Song
2026-09-23 16:34 ` Eduard Zingerman
2026-09-23 18:01 ` Yonghong Song [this message]
2026-09-23 4:59 ` [PATCH bpf-next v5 09/21] bpf: Refuse exception cleanup shapes bpf_throw() cannot dispatch Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 10/21] bpf: Refuse a private stack for a program with an exception cleanup table Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 11/21] bpf: Dispatch exception cleanup pads from bpf_throw() Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 12/21] bpf, x86: Dispatch exception cleanup pads at run time Yonghong Song
2026-09-23 6:45 ` Eduard Zingerman
2026-09-23 20:45 ` Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 13/21] bpf, arm64: " Yonghong Song
2026-09-23 4:59 ` [PATCH bpf-next v5 14/21] libbpf: Resolve the compiler's _Unwind_Resume to the kernel's kfunc Yonghong Song
2026-09-23 8:36 ` Kumar Kartikeya Dwivedi
2026-09-23 5:00 ` [PATCH bpf-next v5 15/21] libbpf: Add cleanup_info to bpf_prog_load_opts Yonghong Song
2026-09-23 5:00 ` [PATCH bpf-next v5 16/21] libbpf: Collect .bpf_cleanup records and pass them to the kernel Yonghong Song
2026-09-23 5:52 ` Kumar Kartikeya Dwivedi
2026-09-23 5:00 ` [PATCH bpf-next v5 17/21] libbpf: Carry the exception cleanup table through the light skeleton Yonghong Song
2026-09-23 5:00 ` [PATCH bpf-next v5 18/21] libbpf: Let the static linker carry .bpf_cleanup relocations Yonghong Song
2026-09-23 5:40 ` bot+bpf-ci
2026-09-23 5:00 ` [PATCH bpf-next v5 19/21] selftests/bpf: Add an end-to-end .bpf_cleanup exception test Yonghong Song
2026-09-23 5:51 ` bot+bpf-ci
2026-09-23 5:00 ` [PATCH bpf-next v5 20/21] selftests/bpf: Cover the exception cleanup shapes the chain does not reach Yonghong Song
2026-09-23 5:51 ` bot+bpf-ci
2026-09-23 7:50 ` Eduard Zingerman
2026-09-23 5:00 ` [PATCH bpf-next v5 21/21] selftests/bpf: Load an exception cleanup program from a light skeleton Yonghong Song
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