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 3068BA94B for ; Mon, 17 Jul 2023 11:18:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7B5BC433C8; Mon, 17 Jul 2023 11:18:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689592688; bh=ZGutFDp51EVykNDckVXlsmgqycUIt04Tp0uAqvCNyEY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WFuZBauGC1k32snt4hy0Mcq71QfzML8QVlqpP1KAgHjSlh86mXpofexhRv6/RLBhh 3Gx/tD6D88oM8N/QUF2HuJ3NgIDlOLDy0+qwqKZNkcg/LQ6mxjdqIQHYCE0ytMT5gy jL4b/hTttKW9RkxjQIbAZayypRi1gn//76ldk5HiBxGrmJ/E4i/zpkLXEtxQjKWVfm HMBy31UTfYn6/HGQ5eQaq5V8BV4n/4HUiGC3kHjIrGo6rL89C5YC2eEeuJLGjZKRdo 3qDOQsnDEZVvJG+xOx9ynpzd4QteD7pI8aXVMXruDTOwPe5rFXEWuow91bjaS7Sm8s uw2OGip3CX/0Q== From: Jiri Olsa To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: bpf@vger.kernel.org, Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo Subject: [PATCH/RFC 2/2] bpf: Disable preemption in bpf_event_output Date: Mon, 17 Jul 2023 13:17:42 +0200 Message-ID: <20230717111742.183926-3-jolsa@kernel.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230717111742.183926-1-jolsa@kernel.org> References: <20230717111742.183926-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit We received report [1] of kernel crash, which is caused by using nesting protection without disabled preemption. The bpf_event_output can be called by programs executed by bpf_prog_run_array_cg function that disabled migration but keeps preemption enabled. This can cause task to be preempted by another one inside the nesting protection and lead eventually to two tasks using same perf_sample_data buffer and cause crashes like: BUG: kernel NULL pointer dereference, address: 0000000000000001 #PF: supervisor instruction fetch in kernel mode #PF: error_code(0x0010) - not-present page ... ? perf_output_sample+0x12a/0x9a0 ? finish_task_switch.isra.0+0x81/0x280 ? perf_event_output+0x66/0xa0 ? bpf_event_output+0x13a/0x190 ? bpf_event_output_data+0x22/0x40 ? bpf_prog_dfc84bbde731b257_cil_sock4_connect+0x40a/0xacb ? xa_load+0x87/0xe0 ? __cgroup_bpf_run_filter_sock_addr+0xc1/0x1a0 ? release_sock+0x3e/0x90 ? sk_setsockopt+0x1a1/0x12f0 ? udp_pre_connect+0x36/0x50 ? inet_dgram_connect+0x93/0xa0 ? __sys_connect+0xb4/0xe0 ? udp_setsockopt+0x27/0x40 ? __pfx_udp_push_pending_frames+0x10/0x10 ? __sys_setsockopt+0xdf/0x1a0 ? __x64_sys_connect+0xf/0x20 ? do_syscall_64+0x3a/0x90 ? entry_SYSCALL_64_after_hwframe+0x72/0xdc Fixing this by disabling preemption in bpf_event_output. [1] https://github.com/cilium/cilium/issues/26756 Reported-by: Oleg "livelace" Popov Fixes: 768fb61fcc13 ("bpf: Fix bpf_event_output re-entry issue") Signed-off-by: Jiri Olsa --- kernel/trace/bpf_trace.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 2a6ba05d8aee..36fb6e483952 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -720,7 +720,6 @@ static DEFINE_PER_CPU(struct bpf_trace_sample_data, bpf_misc_sds); u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy) { - int nest_level = this_cpu_inc_return(bpf_event_output_nest_level); struct perf_raw_frag frag = { .copy = ctx_copy, .size = ctx_size, @@ -737,8 +736,13 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, }; struct perf_sample_data *sd; struct pt_regs *regs; + int nest_level; u64 ret; + preempt_disable(); + + nest_level = this_cpu_inc_return(bpf_event_output_nest_level); + if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bpf_misc_sds.sds))) { ret = -EBUSY; goto out; @@ -753,6 +757,7 @@ u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size, ret = __bpf_perf_event_output(regs, map, flags, sd); out: this_cpu_dec(bpf_event_output_nest_level); + preempt_enable(); return ret; } -- 2.41.0