Somehow recently I frequently hit the following test failure
with either ./test_progs or ./test_progs-cpuv4:
serial_test_ptr_untrusted:PASS:skel_open 0 nsec
serial_test_ptr_untrusted:PASS:lsm_attach 0 nsec
serial_test_ptr_untrusted:PASS:raw_tp_attach 0 nsec
serial_test_ptr_untrusted:FAIL:cmp_tp_name unexpected cmp_tp_name: actual -115 != expected 0
#182 ptr_untrusted:FAIL
Further investigation found the failure is due to
bpf_probe_read_user_str()
where reading user-level string attr->raw_tracepoint.name
is not successfully, most likely due to the
string itself still in disk and not populated into memory yet.
One solution is do a printf() call of the string before doing bpf
syscall which will force the raw_tracepoint.name into memory.
But I think a more robust solution is to use bpf_copy_from_user()
which is used in sleepable program and can tolerate page fault,
and the fix here used the latter approach.
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
tools/testing/selftests/bpf/progs/test_ptr_untrusted.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/bpf/progs/test_ptr_untrusted.c b/tools/testing/selftests/bpf/progs/test_ptr_untrusted.c
index 4bdd65b5aa2d..2fdc44e76624 100644
--- a/tools/testing/selftests/bpf/progs/test_ptr_untrusted.c
+++ b/tools/testing/selftests/bpf/progs/test_ptr_untrusted.c
@@ -6,13 +6,13 @@
char tp_name[128];
-SEC("lsm/bpf")
+SEC("lsm.s/bpf")
int BPF_PROG(lsm_run, int cmd, union bpf_attr *attr, unsigned int size)
{
switch (cmd) {
case BPF_RAW_TRACEPOINT_OPEN:
- bpf_probe_read_user_str(tp_name, sizeof(tp_name) - 1,
- (void *)attr->raw_tracepoint.name);
+ bpf_copy_from_user(tp_name, sizeof(tp_name) - 1,
+ (void *)attr->raw_tracepoint.name);
break;
default:
break;
--
2.34.1
