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bpf: Fail PERF_EVENT_IOC_SET_BPF when bpf_get_[stack|stackid] cannot work

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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@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200723180648.1429892-3-songliubraving@fb.com
This commit is contained in:
Song Liu 2020-07-23 11:06:45 -07:00 committed by Alexei Starovoitov
parent 7b04d6d60f
commit 5d99cb2c86
3 changed files with 23 additions and 1 deletions
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3
include/linux/filter.h
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@ -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 */

3
kernel/bpf/verifier.c
View File

@ -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;

18
kernel/events/core.c
View File

@ -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);