From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A1EDE263F49; Wed, 4 Jun 2025 01:02:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748998941; cv=none; b=quzfRg1Y3xnGrN+RylIdtY9fvacJVGfVQQ0pjiUKmRSD8oDSbLjMZPbsU5UCeqq1JBbOdpTeRDWCJbAH9t11XVIn7WtitLLrGPcvO0J8M1FWx141rwjgdO+rfGAB3IRQ9nu3V6rsTTso+jzw56befHzWR3wRp/NiA3FN5D+xJqE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748998941; c=relaxed/simple; bh=sVrqk7BJazuyKsJJEeaQCd/367FlHz2nJ9AGkwUzIU8=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Trfp1845OibQIiyiM7JtOAFk4uAaDu4Ol2wOPVGaulFbOhHid1Tz+HzcsfoPkmDWFD/PnBjtYj3oBBsUMM98yjEcDqa8exWtZKpkmOIzq0GxPP9HLMWbcrQcTmX6TOLFeR9O3QXo5g7ebe/9+qY48arIZB6w2Zw0GGYhVznffOQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mVgKUsvq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mVgKUsvq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 876B2C4CEF1; Wed, 4 Jun 2025 01:02:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748998941; bh=sVrqk7BJazuyKsJJEeaQCd/367FlHz2nJ9AGkwUzIU8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mVgKUsvq7/fzLsYlJCPm0L0oq2t6S0EdxvAz7lPzi5QDhLbKQ7xDL8Nb2bATtWoPW TtfSDUGmKJ3QSVZNb366AuglfHQOFTW1jJOgMLoIhc9+RtPA/7G58+OptL1n1F6IcQ kX3kz1kS/JFZJBEPkMoD3Nwtk5dajMCp4vPMXnKXwJwdvq3P93Iz35edYiI0oDlCzM b85qS1/drGG1jhDhTiQNFL8yMe1VDe19DCfmb/V2G4YiY2Zsd9AvMCnE9hFZ/NWe8c YeIO84jV4asr7DD1BaAgP8kvFjJjam2jP0UEOh+VYQLtwy4J6D/z+8eBqlvRXb8p6t CpeNQBTHRi3Ww== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Hou Tao , syzbot+dce5aae19ae4d6399986@syzkaller.appspotmail.com, Alexei Starovoitov , Sasha Levin , daniel@iogearbox.net, andrii@kernel.org, bpf@vger.kernel.org Subject: [PATCH AUTOSEL 6.6 05/62] bpf: Check rcu_read_lock_trace_held() in bpf_map_lookup_percpu_elem() Date: Tue, 3 Jun 2025 21:01:16 -0400 Message-Id: <20250604010213.3462-5-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250604010213.3462-1-sashal@kernel.org> References: <20250604010213.3462-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.6.92 Content-Transfer-Encoding: 8bit From: Hou Tao [ Upstream commit d4965578267e2e81f67c86e2608481e77e9c8569 ] bpf_map_lookup_percpu_elem() helper is also available for sleepable bpf program. When BPF JIT is disabled or under 32-bit host, bpf_map_lookup_percpu_elem() will not be inlined. Using it in a sleepable bpf program will trigger the warning in bpf_map_lookup_percpu_elem(), because the bpf program only holds rcu_read_lock_trace lock. Therefore, add the missed check. Reported-by: syzbot+dce5aae19ae4d6399986@syzkaller.appspotmail.com Closes: https://lore.kernel.org/bpf/000000000000176a130617420310@google.com/ Signed-off-by: Hou Tao Link: https://lore.kernel.org/r/20250526062534.1105938-1-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- **YES** This commit should be backported to stable kernel trees based on my analysis: ## Analysis **1. Clear Bug Fix:** This commit fixes a legitimate bug where `bpf_map_lookup_percpu_elem()` triggers warnings in sleepable BPF programs when the BPF JIT is disabled or on 32-bit hosts. The warning occurs because sleepable BPF programs hold `rcu_read_lock_trace` instead of `rcu_read_lock`, but the function only checked for the latter. **2. Minimal, Contained Change:** The fix is extremely small and surgical - it only adds `!rcu_read_lock_trace_held()` to the existing warning condition in `bpf_map_lookup_percpu_elem()` at kernel/bpf/helpers.c:132-133. This follows the exact same pattern established by the previous similar fix. **3. Strong Historical Precedent:** Multiple similar commits have been successfully backported: - **Commit 169410eba271** (Similar Commit #1 - Backport Status: YES) - Added the same `rcu_read_lock_trace_held()` check to `bpf_map_{lookup,update,delete}_elem()` helpers with identical reasoning - **Commit 29a7e00ffadd** (Similar Commit #4 - Backport Status: YES) - Fixed missed RCU read lock in `bpf_task_under_cgroup()` for sleepable programs **4. Clear User Impact:** The commit was reported by syzbot and fixes a concrete issue affecting users running sleepable BPF programs. Without this fix, users see spurious warnings that indicate potential RCU usage bugs. **5. Low Regression Risk:** The change only expands the conditions under which the warning is suppressed - it doesn't change any functional behavior, just makes the assertion more accurate for sleepable BPF programs. **6. Part of Ongoing Pattern:** This is the missing piece in a series of similar fixes that have systematically addressed RCU assertions for sleepable BPF programs. The previous commit 169410eba271 fixed the basic map helpers but missed this percpu variant. **7. Stable Tree Criteria Alignment:** - Fixes important functionality (eliminates false warnings) - No architectural changes - Minimal risk of regression - Confined to BPF subsystem - Clear side effects (none beyond fixing the warning) The commit perfectly matches the stable tree backporting criteria and follows the established pattern of similar successful backports. kernel/bpf/helpers.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 41d62405c8521..8f0b62b04deeb 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -128,7 +128,8 @@ const struct bpf_func_proto bpf_map_peek_elem_proto = { BPF_CALL_3(bpf_map_lookup_percpu_elem, struct bpf_map *, map, void *, key, u32, cpu) { - WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_bh_held()); + WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_trace_held() && + !rcu_read_lock_bh_held()); return (unsigned long) map->ops->map_lookup_percpu_elem(map, key, cpu); } -- 2.39.5