Commit 5d99cb2c authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

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: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723180648.1429892-3-songliubraving@fb.com
parent 7b04d6d6

include/linux/filter.h

+2 −1
Original line number Diff line number Diff line
@@ -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 */

kernel/bpf/verifier.c

+3 −0
Original line number Diff line number Diff line
@@ -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;

kernel/events/core.c

+18 −0
Original line number Diff line number Diff line
@@ -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);