From: Yonghong Song <yonghong.song@linux.dev>
To: sashiko-reviews@lists.linux.dev
Cc: bpf@vger.kernel.org
Subject: Re: [PATCH bpf-next v6 11/21] bpf, x86: Dispatch exception cleanup pads at run time
Date: Sat, 26 Sep 2026 21:35:32 -0700 [thread overview]
Message-ID: <c30b6d55-1ef1-4b9a-a434-99b7f3834bb4@linux.dev> (raw)
In-Reply-To: <20260926051542.4DF841F000FF@smtp.kernel.org>
On 9/25/26 10:15 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] bpf, x86: missing JIT epilogue for exit-less subprograms crashes exception unwinder
> --
>
> commit 9bb870f715bdf91026578628a6afaf5325f80183
> Author: Yonghong Song <yonghong.song@linux.dev>
>
> bpf, x86: Dispatch exception cleanup pads at run time
>
> This commit updates the x86 BPF JIT to dispatch exception cleanup pads at run
> time, setting up native cleanup tables and populating the epilogue IP to allow
> redirecting a frame to its landing pad during an ORC stack walk.
>
>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>> index 6c7a0578760e7..fb7e8ca1aab21 100644
>> --- a/arch/x86/net/bpf_jit_comp.c
>> +++ b/arch/x86/net/bpf_jit_comp.c
> [ ... ]
>
>> @@ -3278,6 +3279,8 @@ static int do_jit(struct bpf_verifier_env *env, struct bpf_prog *bpf_prog, int *
>> seen_exit = true;
>> /* Update cleanup_addr */
>> ctx->cleanup_addr = proglen;
>> + /* Where an unwind sends a frame with no pad. */
>> + bpf_prog->aux->epilogue_ip = (u64)image + proglen;
> [Severity: High]
> What happens if a BPF subprogram only terminates via a noreturn kfunc like
> bpf_throw(), meaning it lacks a BPF_EXIT instruction entirely?
bpf_throw() will be rejected if landing_pad is available.
>
> Since the x86 JIT generates the epilogue lazily when the first BPF_EXIT is
> encountered, wouldn't do_jit() produce no epilogue at all for such a program,
> leaving epilogue_ip as 0?
>
> If an exception unwinds through this subprogram's frame, the unwinder relies
> on epilogue_ip to rewrite the return address. Wouldn't it hit this error path
> and abort the unwind?
>
> kernel/bpf/helpers.c:bpf_unwind_rewrite() {
> ...
> } else if (prog->aux->epilogue_ip) {
> *ra = prog->aux->epilogue_ip;
> } else {
> WARN_ON_ONCE(1);
> return false;
> }
> }
>
> Could this lead to corrupted exception handling that can be triggered by
> user-supplied BPF programs?
Yes, it is possible that epilogue_ip is 0 if that subprog is always
in the path when unwinding happens. The fix will be keep 'exit' insn's
so they won'be removed. See bpf_jit_comp.c
case BPF_JMP | BPF_EXIT:
if (seen_exit) {
jmp_offset = ctx->cleanup_addr - addrs[i];
goto emit_jmp;
}
seen_exit = true;
/* Update cleanup_addr */
ctx->cleanup_addr = proglen;
/* Where an unwind sends a frame with no pad. */
bpf_prog->aux->epilogue_ip = (u64)image + proglen;
...
>
>> if (bpf_prog_was_classic(bpf_prog) &&
>> !ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN)) {
>> if (emit_spectre_bhb_barrier(&prog, ip, bpf_prog))
> [ ... ]
>
next prev parent reply other threads:[~2026-09-27 4:35 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-26 5:00 [PATCH bpf-next v6 00/21] bpf: Run exception cleanup landing pads when bpf_unwind() unwinds Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 01/21] bpf: Pack bpf_insn_aux_data flags into bit fields Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 02/21] bpf: Accept the compiler's exception cleanup table at program load Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 03/21] bpf: Add the bpf_unwind() and bpf_unwind_resume() kfuncs Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 04/21] bpf: Add lookups for exception cleanup resumes and landing pads Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 05/21] bpf: Prepare for an exception cleanup table before the CFG walk Yonghong Song
2026-09-26 5:16 ` sashiko-bot
2026-09-26 23:54 ` Yonghong Song
2026-09-27 20:39 ` bot+bpf-ci
2026-09-28 0:01 ` Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 06/21] bpf: Make exception landing pads reachable in the CFG Yonghong Song
2026-09-26 5:21 ` sashiko-bot
2026-09-27 0:02 ` Yonghong Song
2026-09-27 20:40 ` bot+bpf-ci
2026-09-28 0:12 ` Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 07/21] bpf: Resume a covered call at its landing pad Yonghong Song
2026-09-26 5:15 ` sashiko-bot
2026-09-26 8:21 ` Alexei Starovoitov
2026-09-27 0:04 ` Yonghong Song
2026-09-27 0:41 ` Yonghong Song
2026-09-27 20:40 ` bot+bpf-ci
2026-09-28 0:17 ` Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 08/21] bpf: Refuse a landing pad that does not resume Yonghong Song
2026-09-26 5:17 ` sashiko-bot
2026-09-27 3:06 ` Yonghong Song
2026-09-27 20:40 ` bot+bpf-ci
2026-09-28 0:29 ` Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 09/21] bpf: Refuse a private stack for a program with an exception cleanup table Yonghong Song
2026-09-26 5:00 ` [PATCH bpf-next v6 10/21] bpf: Dispatch cleanup pads by rewriting return addresses Yonghong Song
2026-09-27 20:40 ` bot+bpf-ci
2026-09-28 1:08 ` Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 11/21] bpf, x86: Dispatch exception cleanup pads at run time Yonghong Song
2026-09-26 5:15 ` sashiko-bot
2026-09-27 4:35 ` Yonghong Song [this message]
2026-09-27 20:39 ` bot+bpf-ci
2026-09-28 3:10 ` Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 12/21] bpf, arm64: " Yonghong Song
2026-09-26 5:14 ` sashiko-bot
2026-09-27 20:40 ` bot+bpf-ci
2026-09-26 5:01 ` [PATCH bpf-next v6 13/21] libbpf: Resolve the compiler's _Unwind_Resume to the kernel's kfunc Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 14/21] libbpf: Add cleanup_info to bpf_prog_load_opts Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 15/21] libbpf: Collect .bpf_cleanup records and pass them to the kernel Yonghong Song
2026-09-27 20:39 ` bot+bpf-ci
2026-09-28 3:28 ` Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 16/21] libbpf: Carry the exception cleanup table through the light skeleton Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 17/21] libbpf: Let the static linker carry .bpf_cleanup relocations Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 18/21] selftests/bpf: Add an end-to-end .bpf_cleanup exception test Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 19/21] selftests/bpf: Add __set_global() and __ret_global() test tags Yonghong Song
2026-09-26 5:18 ` sashiko-bot
2026-09-27 4:58 ` Yonghong Song
2026-09-27 20:24 ` bot+bpf-ci
2026-09-28 3:36 ` Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 20/21] selftests/bpf: Cover the exception cleanup shapes the chain does not reach Yonghong Song
2026-09-27 20:40 ` bot+bpf-ci
2026-09-28 3:49 ` Yonghong Song
2026-09-26 5:01 ` [PATCH bpf-next v6 21/21] selftests/bpf: Load an exception cleanup program from a light skeleton Yonghong Song
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