Calling get_perf_callchain() on perf_events from PEBS entries may cause
unwinder errors. To fix this issue, the callchain is fetched early. Such
perf_events are marked with __PERF_SAMPLE_CALLCHAIN_EARLY.
Similarly, calling bpf_get_[stack|stackid] on perf_events from PEBS may
also cause unwinder errors. To fix this, block bpf_get_[stack|stackid] on
these perf_events. Unfortunately, bpf verifier cannot tell whether the
program will be attached to perf_event with PEBS entries. Therefore,
block such programs during ioctl(PERF_EVENT_IOC_SET_BPF).
Signed-off-by: Song Liu <songliubrav...@fb.com>
---
include/linux/filter.h | 3 ++-
kernel/bpf/verifier.c | 3 +++
kernel/events/core.c | 10 ++++++++++
3 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 2593777236037..fb34dc40f039b 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -534,7 +534,8 @@ 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_perf_callchain:1; /* Do we call
helpers that uses get_perf_callchain()? */
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 b608185e1ffd5..1e11b0f6fba31 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4884,6 +4884,9 @@ 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_perf_callchain = 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..f2f575a286bb4 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9544,6 +9544,16 @@ 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.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) &&
+ prog->call_get_perf_callchain) {
+ /*
+ * The perf_event get_perf_callchain() early, the attached
+ * BPF program shouldn't call get_perf_callchain() again.
+ */
+ bpf_prog_put(prog);
+ return -EINVAL;
+ }
+
event->prog = prog;
event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
--
2.24.1
