[PATCHv3 bpf-next 5/6] bpf: Return value in kprobe get_func_ip only for entry address

[Jiri Olsa <jolsa@xxxxxxxxxx>]

Changing return value of kprobe's version of bpf_get_func_ip
to return zero if the attach address is not on the function's
entry point.

For kprobes attached in the middle of the function we can't easily
get to the function address especially now with the CONFIG_X86_KERNEL_IBT
support.

If user cares about current IP for kprobes attached within the
function body, they can get it with PT_REGS_IP(ctx).

Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 kernel/trace/bpf_trace.c                             | 11 ++++++++++-
 tools/testing/selftests/bpf/progs/get_func_ip_test.c |  4 ++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index bcada91b0b3b..027abc38faab 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1029,8 +1029,17 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = {
 BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
 {
 	struct kprobe *kp = kprobe_running();
+	uintptr_t addr;
 
-	return kp ? (uintptr_t)kp->addr : 0;
+	if (!kp || !(kp->flags & KPROBE_FLAG_ON_FUNC_ENTRY))
+		return 0;
+
+	addr = (uintptr_t)kp->addr;
+#ifdef CONFIG_X86_KERNEL_IBT
+	if (is_endbr(*((u32 *) addr - 1)))
+		addr -= ENDBR_INSN_SIZE;
+#endif
+	return addr;
 }
 
 static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
index a587aeca5ae0..6db70757bc8b 100644
--- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
+++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
@@ -69,7 +69,7 @@ int test6(struct pt_regs *ctx)
 {
 	__u64 addr = bpf_get_func_ip(ctx);
 
-	test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
+	test6_result = (const void *) addr == 0;
 	return 0;
 }
 
@@ -79,6 +79,6 @@ int test7(struct pt_regs *ctx)
 {
 	__u64 addr = bpf_get_func_ip(ctx);
 
-	test7_result = (const void *) addr == &bpf_fentry_test7 + 5;
+	test7_result = (const void *) addr == 0;
 	return 0;
 }
-- 
2.37.3