linux-kernel - [PATCH v5 bpf-next 2/5] bpf: fail PERF_EVENT_IOC_SET_BPF when bpf_get

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Message-ID: <20200723180648.1429892-3-songliubraving@fb.com>
Date:   Thu, 23 Jul 2020 11:06:45 -0700
From:   Song Liu <songliubraving@...com>
To:     <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <kernel-team@...com>,
        <john.fastabend@...il.com>, <kpsingh@...omium.org>,
        <brouer@...hat.com>, <peterz@...radead.org>,
        Song Liu <songliubraving@...com>
Subject: [PATCH v5 bpf-next 2/5] bpf: fail PERF_EVENT_IOC_SET_BPF when bpf_get_[stack|stackid] cannot work

bpf_get_[stack|stackid] on perf_events with precise_ip uses callchain
attached to perf_sample_data. If this callchain is not presented, do not
allow attaching BPF program that calls bpf_get_[stack|stackid] to this
event.

In the error case, -EPROTO is returned so that libbpf can identify this
error and print proper hint message.

Signed-off-by: Song Liu <songliubraving@...com>
---
 include/linux/filter.h |  3 ++-
 kernel/bpf/verifier.c  |  3 +++
 kernel/events/core.c   | 18 ++++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1c6b6d982bf49..135692027dd8b 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -532,7 +532,8 @@ struct bpf_prog {
 				is_func:1,	/* program is a bpf function */
 				kprobe_override:1, /* Do we override a kprobe? */
 				has_callchain_buf:1, /* callchain buffer allocated? */
-				enforce_expected_attach_type:1; /* Enforce expected_attach_type checking at attach time */
+				enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */
+				call_get_stack:1; /* Do we call bpf_get_stack() or bpf_get_stackid() */
 	enum bpf_prog_type	type;		/* Type of BPF program */
 	enum bpf_attach_type	expected_attach_type; /* For some prog types */
 	u32			len;		/* Number of filter blocks */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9a6703bc3f36f..41c9517a505ff 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4887,6 +4887,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 		env->prog->has_callchain_buf = true;
 	}
 
+	if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)
+		env->prog->call_get_stack = true;
+
 	if (changes_data)
 		clear_all_pkt_pointers(env);
 	return 0;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 856d98c36f562..ddcfd2fb5cc5a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9544,6 +9544,24 @@ static int perf_event_set_bpf_handler(struct perf_event *event, u32 prog_fd)
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
 
+	if (event->attr.precise_ip &&
+	    prog->call_get_stack &&
+	    (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) ||
+	     event->attr.exclude_callchain_kernel ||
+	     event->attr.exclude_callchain_user)) {
+		/*
+		 * On perf_event with precise_ip, calling bpf_get_stack()
+		 * may trigger unwinder warnings and occasional crashes.
+		 * bpf_get_[stack|stackid] works around this issue by using
+		 * callchain attached to perf_sample_data. If the
+		 * perf_event does not full (kernel and user) callchain
+		 * attached to perf_sample_data, do not allow attaching BPF
+		 * program that calls bpf_get_[stack|stackid].
+		 */
+		bpf_prog_put(prog);
+		return -EPROTO;
+	}
+
 	event->prog = prog;
 	event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
 	WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
-- 
2.24.1