From: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>
To: <bot+bpf-ci@kernel.org>, <florent.revest@linux.dev>,
<bpf@vger.kernel.org>, <daniel@iogearbox.net>,
<andrii@kernel.org>
Cc: <martin.lau@linux.dev>, <eddyz87@gmail.com>, <memxor@gmail.com>,
<song@kernel.org>, <yonghong.song@linux.dev>, <jolsa@kernel.org>,
<kpsingh@kernel.org>, <john.fastabend@gmail.com>,
<leon.hwang@linux.dev>, <zirajs7@gmail.com>,
<rhkrqnwk98@gmail.com>, <puranjay@kernel.org>,
<xukuohai@huaweicloud.com>, <iii@linux.ibm.com>,
<hbathini@linux.ibm.com>, <chleroy@kernel.org>,
<naveen@kernel.org>, <bjorn@kernel.org>, <pulehui@huawei.com>,
<yangtiezhu@loongson.cn>, <hengqi.chen@gmail.com>,
<linux-kernel@vger.kernel.org>, <martin.lau@kernel.org>,
<mason@kernel.org>, <ihor.solodrai@linux.dev>
Subject: Re: [PATCH bpf v4 2/3] bpf: Skip detached progs in trampoline images that are still in use
Date: Sat, 26 Sep 2026 08:44:13 +0000 [thread overview]
Message-ID: <DLP46AE97EYD.1I2HDPGBR8GME@gmail.com> (raw)
In-Reply-To: <6a6d43e6bada7a1433cd525c9ec31780ed9b2401c8834894defdf671601b2f1d@mail.kernel.org>
On Fri, Sep 25, 2026 at 10:47 AM bot+bpf-ci@kernel.org <bot+bpf-ci@kernel.org> wrote:
>> + /* nops for move_imm+jirl, patched to skip this prog when it is detached */
>> + for (i = 0; i < LOONGARCH_LONG_JUMP_NINSNS; i++)
>> + emit_insn(ctx, nop);
>
> Can a task preempted inside the skip sled resume into half of the new jump
> sequence and jump to a garbage address?
[...]
> Could the LoongArch skip site use a single instruction instead? For
> example, a 'b' to the skip target, which is always within the +/-128MB
> range of the same image, patched from nop to 'b'. The rest of the sled
> would then be unnecessary.
Seems like a real bug. Same issue on riscv.
ip_after_call was patched in bpf_tramp_image_put() when the image was
already unreachable. Now bpf_trampoline_remove_prog() patches cur_image
before bpf_trampoline_update() replaces it, so every call of the traced
function goes through the sled while it is rewritten. stop_machine
doesn't help the task that it preempted in the middle of the sled.
Pls fix and respin.
Everything else looks good.
pw-bot: cr
next prev parent reply other threads:[~2026-09-26 8:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-25 10:03 [PATCH bpf v4 0/3] bpf: Fix use-after-free of progs detached from busy trampolines Florent Revest (Anthropic)
2026-09-25 10:03 ` [PATCH bpf v4 1/3] bpf: Wait for an RCU tasks grace period before freeing trampoline progs Florent Revest (Anthropic)
2026-09-25 10:47 ` bot+bpf-ci
2026-09-26 13:54 ` Florent Revest
2026-09-25 10:03 ` [PATCH bpf v4 2/3] bpf: Skip detached progs in trampoline images that are still in use Florent Revest (Anthropic)
2026-09-25 10:47 ` bot+bpf-ci
2026-09-26 8:44 ` Alexei Starovoitov [this message]
2026-09-26 13:52 ` Florent Revest
2026-09-26 13:54 ` Florent Revest
2026-09-25 10:03 ` [PATCH bpf v4 3/3] selftests/bpf: Detach a trampoline prog while a task sleeps before it Florent Revest (Anthropic)
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