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 <[email protected]> Signed-off-by: Alexei Starovoitov <[email protected]> Link: https://lore.kernel.org/bpf/[email protected]
mrcsosa · Jul 26, 2020 · 5d99cb2 · 5d99cb2
1 parent 7b04d6d
commit 5d99cb2
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Showing 3 changed files with 23 additions and 1 deletion.
diff --git a/include/linux/filter.h b/include/linux/filter.h
@@ -533,7 +533,8 @@ 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
@@ -4962,6 +4962,9 @@ 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
@@ -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);