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 5BCECA94B for ; Mon, 17 Jul 2023 11:17:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6FCE9C433C7; Mon, 17 Jul 2023 11:17:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689592678; bh=jot9s6fLV7YrNQasRJBwZMKV369kRyq6kqHobeALIwg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GS/Fh5M1fS187Qfw9mCTApDFqouHgLFCnXlBrW4Nl7VJc+f24+X6nuYsRAn8ACi1j 8aZAOKpPASXOB1ubNFoKcjsypJAwS3itl/eCB6OIvi9h9M6vAwuh6Fbt420gQt3ATj 6v9YrdStqTT2OLtuO2ouKkgeEuZQCFo+ZIsHIewIVHz+M9cUwI/doRuHPEvThWJY1s o7Ihwismojqpsgbqbtb2UhmNGo2XYD+wKZquWyYYSClcLaH65YWvKIXVOF6mJX01MY prLLvQw4iFKsKLSFJLdk8Dp1ob82GxZKFnhh3Mge78kmvo6OAPSIdwxjVeLDoRlWTp NuK1oCZ3zJ0EA== 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 1/2] bpf: Disable preemption in bpf_perf_event_output Date: Mon, 17 Jul 2023 13:17:41 +0200 Message-ID: <20230717111742.183926-2-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 The nesting protection in bpf_perf_event_output relies on disabled preemption, which is guaranteed for kprobes and tracepoints. However bpf_perf_event_output can be also called from uprobes context through bpf_prog_run_array_sleepable function which disables 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: kernel tried to execute NX-protected page - exploit attempt? (uid: 0) BUG: unable to handle page fault for address: ffffffff82be3eea ... Call Trace: ? __die+0x1f/0x70 ? page_fault_oops+0x176/0x4d0 ? exc_page_fault+0x132/0x230 ? asm_exc_page_fault+0x22/0x30 ? perf_output_sample+0x12b/0x910 ? perf_event_output+0xd0/0x1d0 ? bpf_perf_event_output+0x162/0x1d0 ? bpf_prog_c6271286d9a4c938_krava1+0x76/0x87 ? __uprobe_perf_func+0x12b/0x540 ? uprobe_dispatcher+0x2c4/0x430 ? uprobe_notify_resume+0x2da/0xce0 ? atomic_notifier_call_chain+0x7b/0x110 ? exit_to_user_mode_prepare+0x13e/0x290 ? irqentry_exit_to_user_mode+0x5/0x30 ? asm_exc_int3+0x35/0x40 Fixing this by disabling preemption in bpf_perf_event_output. Fixes: 9594dc3c7e71 ("bpf: fix nested bpf tracepoints with per-cpu data") Signed-off-by: Jiri Olsa --- kernel/trace/bpf_trace.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index c92eb8c6ff08..2a6ba05d8aee 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -661,8 +661,7 @@ static DEFINE_PER_CPU(int, bpf_trace_nest_level); BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map, u64, flags, void *, data, u64, size) { - struct bpf_trace_sample_data *sds = this_cpu_ptr(&bpf_trace_sds); - int nest_level = this_cpu_inc_return(bpf_trace_nest_level); + struct bpf_trace_sample_data *sds; struct perf_raw_record raw = { .frag = { .size = size, @@ -670,7 +669,12 @@ BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map, }, }; struct perf_sample_data *sd; - int err; + int nest_level, err; + + preempt_disable(); + + sds = this_cpu_ptr(&bpf_trace_sds); + nest_level = this_cpu_inc_return(bpf_trace_nest_level); if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(sds->sds))) { err = -EBUSY; @@ -691,6 +695,7 @@ BPF_CALL_5(bpf_perf_event_output, struct pt_regs *, regs, struct bpf_map *, map, out: this_cpu_dec(bpf_trace_nest_level); + preempt_enable(); return err; } -- 2.41.0