From: "Kumar Kartikeya Dwivedi" <memxor@gmail.com>
To: "Björn Töpel" <bjorn@kernel.org>,
"Feng Jiang" <jiangfeng@kylinos.cn>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andrii@kernel.org>,
"Eduard Zingerman" <eddyz87@gmail.com>,
"Martin KaFai Lau" <martin.lau@linux.dev>,
"Song Liu" <song@kernel.org>,
"Yonghong Song" <yonghong.song@linux.dev>,
"Jiri Olsa" <jolsa@kernel.org>,
"Emil Tsalapatis" <emil@etsalapatis.com>,
"Pu Lehui" <pulehui@huawei.com>,
"Puranjay Mohan" <puranjay@kernel.org>,
"Paul Walmsley" <pjw@kernel.org>,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Albert Ou" <aou@eecs.berkeley.edu>,
"Alexandre Ghiti" <alex@ghiti.fr>
Cc: "Björn Töpel" <bjorn@rivosinc.com>,
bpf@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] bpf, riscv: fix extable handling for arena load_acquire
Date: Tue, 21 Jul 2026 20:25:44 +0200 [thread overview]
Message-ID: <DK4GL1CICEHY.10XAOFWAEHJCJ@gmail.com> (raw)
In-Reply-To: <87h5lsurzn.fsf@all.your.base.are.belong.to.us>
On Tue Jul 21, 2026 at 8:17 PM CEST, Björn Töpel wrote:
> Feng Jiang <jiangfeng@kylinos.cn> writes:
>
>> emit_atomic_ld_st() returns 1 to have build_body() skip the zext after
>> a sub-word load_acquire. The caller does "ret = ret ?:
>> add_exception_handler(...)", which skips add_exception_handler() on any
>> non-zero ret, so the extable entry is missing and a faulting
>> PROBE_ATOMIC load_acquire oopses.
>>
>> REG_DONT_CLEAR_MARKER leaves rd stale on fault, and the verifier still
>> thinks the load overwrote it, so a program can leak it through a map.
>>
>> Check ret >= 0 before calling add_exception_handler(), and pass rd for
>> LOAD_ACQ so the fault zeroes rd like a PROBE_MEM load. Return ret
>> unchanged for the zext skip.
>>
>> Fixes: fb7cefabae81 ("riscv, bpf: Add support arena atomics for RV64")
>> Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>
>
> Thank you for spinning a new version!
>
> Reviewed-by: Björn Töpel <bjorn@kernel.org>
> Acked-by: Björn Töpel <bjorn@kernel.org>
There was an identical v4 resend. I applied the acks there and pushed.
Thanks.
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prev parent reply other threads:[~2026-07-21 18:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-20 6:06 [PATCH v3] bpf, riscv: fix extable handling for arena load_acquire Feng Jiang
2026-07-21 18:17 ` Björn Töpel
2026-07-21 18:25 ` Kumar Kartikeya Dwivedi [this message]
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