selftests/bpf: Fix test_vmlinux test to use bpf_probe_read_user()

The test is reading UAPI kernel structure from user-space. So it doesn't need
CO-RE relocations and has to use bpf_probe_read_user().

Fixes: acbd0620 ("selftests/bpf: Add vmlinux.h selftest exercising tracing of syscalls")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200818213356.2629020-6-andriin@fb.com

tools/testing/selftests/bpf/progs/test_vmlinux.c

@@ -19,12 +19,14 @@ SEC("tp/syscalls/sys_enter_nanosleep")
 int handle__tp(struct trace_event_raw_sys_enter *args)
 {
 	struct __kernel_timespec *ts;
+	long tv_nsec;
 
 	if (args->id != __NR_nanosleep)
 		return 0;
 
 	ts = (void *)args->args[0];
-	if (BPF_CORE_READ(ts, tv_nsec) != MY_TV_NSEC)
+	if (bpf_probe_read_user(&tv_nsec, sizeof(ts->tv_nsec), &ts->tv_nsec) ||
+	    tv_nsec != MY_TV_NSEC)
 		return 0;
 
 	tp_called = true;
@@ -35,12 +37,14 @@ SEC("raw_tp/sys_enter")
 int BPF_PROG(handle__raw_tp, struct pt_regs *regs, long id)
 {
 	struct __kernel_timespec *ts;
+	long tv_nsec;
 
 	if (id != __NR_nanosleep)
 		return 0;
 
 	ts = (void *)PT_REGS_PARM1_CORE(regs);
-	if (BPF_CORE_READ(ts, tv_nsec) != MY_TV_NSEC)
+	if (bpf_probe_read_user(&tv_nsec, sizeof(ts->tv_nsec), &ts->tv_nsec) ||
+	    tv_nsec != MY_TV_NSEC)
 		return 0;
 
 	raw_tp_called = true;
@@ -51,12 +55,14 @@ SEC("tp_btf/sys_enter")
 int BPF_PROG(handle__tp_btf, struct pt_regs *regs, long id)
 {
 	struct __kernel_timespec *ts;
+	long tv_nsec;
 
 	if (id != __NR_nanosleep)
 		return 0;
 
 	ts = (void *)PT_REGS_PARM1_CORE(regs);
-	if (BPF_CORE_READ(ts, tv_nsec) != MY_TV_NSEC)
+	if (bpf_probe_read_user(&tv_nsec, sizeof(ts->tv_nsec), &ts->tv_nsec) ||
+	    tv_nsec != MY_TV_NSEC)
 		return 0;
 
 	tp_btf_called = true;