[PATCHv5 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>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Martynas Pumputis <m@xxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
 include/uapi/linux/bpf.h                             | 1 +
 kernel/trace/bpf_trace.c                             | 5 ++++-
 tools/include/uapi/linux/bpf.h                       | 1 +
 tools/testing/selftests/bpf/progs/get_func_ip_test.c | 4 ++--
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ead35f39f185..d6bd10759eaf 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4951,6 +4951,7 @@ union bpf_attr {
  * 		Get address of the traced function (for tracing and kprobe programs).
  * 	Return
  * 		Address of the traced function.
+ * 		0 for kprobes placed within the function (not at the entry).
  *
  * u64 bpf_get_attach_cookie(void *ctx)
  * 	Description
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index ebd1b348beb3..688552df95ca 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1048,7 +1048,10 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
 {
 	struct kprobe *kp = kprobe_running();
 
-	return kp ? (uintptr_t)kp->addr : 0;
+	if (!kp || !(kp->flags & KPROBE_FLAG_ON_FUNC_ENTRY))
+		return 0;
+
+	return get_entry_ip((uintptr_t)kp->addr);
 }
 
 static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index ead35f39f185..d6bd10759eaf 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4951,6 +4951,7 @@ union bpf_attr {
  * 		Get address of the traced function (for tracing and kprobe programs).
  * 	Return
  * 		Address of the traced function.
+ * 		0 for kprobes placed within the function (not at the entry).
  *
  * u64 bpf_get_attach_cookie(void *ctx)
  * 	Description
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