Subject: [PATCH 02/13] kprobe: Keep traced function address

From: Jiri Olsa <[email-masked]>
Date: Tue, 4 Jan 2022 09:09:32 +0100

The bpf_get_func_ip_kprobe helper should return traced function
address, but it's doing so only for kprobes that are placed on
the function entry.

If kprobe is placed within the function, bpf_get_func_ip_kprobe
returns that address instead of function entry.

Storing the function entry directly in kprobe object, so it could
be used in bpf_get_func_ip_kprobe helper.

Signed-off-by: Jiri Olsa <[email-masked]>
---
 include/linux/kprobes.h                              |  3 +++
 kernel/kprobes.c                                     | 12 ++++++++++++
 kernel/trace/bpf_trace.c                             |  2 +-
 tools/testing/selftests/bpf/progs/get_func_ip_test.c |  4 ++--
 4 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8c8f7a4d93af..a204df4fef96 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -74,6 +74,9 @@ struct kprobe {
 	/* Offset into the symbol */
 	unsigned int offset;
 
+	/* traced function address */
+	unsigned long func_addr;
+
 	/* Called before addr is executed. */
 	kprobe_pre_handler_t pre_handler;
 
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d20ae8232835..c4060a8da050 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1310,6 +1310,7 @@ static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
 	copy_kprobe(p, ap);
 	flush_insn_slot(ap);
 	ap->addr = p->addr;
+	ap->func_addr = p->func_addr;
 	ap->flags = p->flags & ~KPROBE_FLAG_OPTIMIZED;
 	ap->pre_handler = aggr_pre_handler;
 	/* We don't care the kprobe which has gone. */
@@ -1588,6 +1589,16 @@ static int check_kprobe_address_safe(struct kprobe *p,
 	return ret;
 }
 
+static unsigned long resolve_func_addr(kprobe_opcode_t *addr)
+{
+	char str[KSYM_SYMBOL_LEN];
+	unsigned long offset;
+
+	if (kallsyms_lookup((unsigned long) addr, NULL, &offset, NULL, str))
+		return (unsigned long) addr - offset;
+	return 0;
+}
+
 int register_kprobe(struct kprobe *p)
 {
 	int ret;
@@ -1600,6 +1611,7 @@ int register_kprobe(struct kprobe *p)
 	if (IS_ERR(addr))
 		return PTR_ERR(addr);
 	p->addr = addr;
+	p->func_addr = resolve_func_addr(addr);
 
 	ret = warn_kprobe_rereg(p);
 	if (ret)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 21aa30644219..25631253084a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1026,7 +1026,7 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
 {
 	struct kprobe *kp = kprobe_running();
 
-	return kp ? (uintptr_t)kp->addr : 0;
+	return kp ? (uintptr_t)kp->func_addr : 0;
 }
 
 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..e988aefa567e 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 == &bpf_fentry_test6;
 	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 == &bpf_fentry_test7;
 	return 0;
 }
-- 
2.33.1