fprobe: Skip exit_handler if entry_handler returns !0

Skip hooking function return and calling exit_handler if the
entry_handler() returns !0.

Link: https://lkml.kernel.org/r/167526699798.433354.10998365726830117303.stgit@mhiramat.roam.corp.google.com

Cc: Florent Revest <revest@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/linux/fprobe.h

@@ -34,8 +34,8 @@ struct fprobe {
 	size_t			entry_data_size;
 	int			nr_maxactive;
 
-	void (*entry_handler)(struct fprobe *fp, unsigned long entry_ip,
-			      struct pt_regs *regs, void *entry_data);
+	int (*entry_handler)(struct fprobe *fp, unsigned long entry_ip,
+			     struct pt_regs *regs, void *entry_data);
 	void (*exit_handler)(struct fprobe *fp, unsigned long entry_ip,
 			     struct pt_regs *regs, void *entry_data);
 };

kernel/trace/bpf_trace.c

@@ -2644,12 +2644,23 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
 	return err;
 }
 
-static void
+static int
 kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip,
 			  struct pt_regs *regs, void *data)
 {
 	struct bpf_kprobe_multi_link *link;
 
+	link = container_of(fp, struct bpf_kprobe_multi_link, fp);
+	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
+	return 0;
+}
+
+static void
+kprobe_multi_link_exit_handler(struct fprobe *fp, unsigned long fentry_ip,
+			       struct pt_regs *regs, void *data)
+{
+	struct bpf_kprobe_multi_link *link;
+
 	link = container_of(fp, struct bpf_kprobe_multi_link, fp);
 	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
 }
@@ -2848,7 +2859,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 		goto error;
 
 	if (flags & BPF_F_KPROBE_MULTI_RETURN)
-		link->fp.exit_handler = kprobe_multi_link_handler;
+		link->fp.exit_handler = kprobe_multi_link_exit_handler;
 	else
 		link->fp.entry_handler = kprobe_multi_link_handler;
 

kernel/trace/fprobe.c

@@ -27,7 +27,7 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
 	struct rethook_node *rh = NULL;
 	struct fprobe *fp;
 	void *entry_data = NULL;
-	int bit;
+	int bit, ret;
 
 	fp = container_of(ops, struct fprobe, ops);
 	if (fprobe_disabled(fp))
@@ -52,11 +52,15 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip,
 	}
 
 	if (fp->entry_handler)
-		fp->entry_handler(fp, ip, ftrace_get_regs(fregs), entry_data);
-
-	if (rh)
-		rethook_hook(rh, ftrace_get_regs(fregs), true);
+		ret = fp->entry_handler(fp, ip, ftrace_get_regs(fregs), entry_data);
 
+	/* If entry_handler returns !0, nmissed is not counted. */
+	if (rh) {
+		if (ret)
+			rethook_recycle(rh);
+		else
+			rethook_hook(rh, ftrace_get_regs(fregs), true);
+	}
 out:
 	ftrace_test_recursion_unlock(bit);
 }

lib/test_fprobe.c

@@ -37,7 +37,7 @@ static noinline u32 fprobe_selftest_nest_target(u32 value, u32 (*nest)(u32))
 	return nest(value + 2);
 }
 
-static notrace void fp_entry_handler(struct fprobe *fp, unsigned long ip,
+static notrace int fp_entry_handler(struct fprobe *fp, unsigned long ip,
 				     struct pt_regs *regs, void *data)
 {
 	KUNIT_EXPECT_FALSE(current_test, preemptible());
@@ -51,6 +51,8 @@ static notrace void fp_entry_handler(struct fprobe *fp, unsigned long ip,
 			*(u32 *)data = entry_val;
 	} else
 		KUNIT_EXPECT_NULL(current_test, data);
+
+	return 0;
 }
 
 static notrace void fp_exit_handler(struct fprobe *fp, unsigned long ip,
@@ -74,10 +76,11 @@ static notrace void fp_exit_handler(struct fprobe *fp, unsigned long ip,
 		KUNIT_EXPECT_NULL(current_test, data);
 }
 
-static notrace void nest_entry_handler(struct fprobe *fp, unsigned long ip,
+static notrace int nest_entry_handler(struct fprobe *fp, unsigned long ip,
 				     struct pt_regs *regs, void *data)
 {
 	KUNIT_EXPECT_FALSE(current_test, preemptible());
+	return 0;
 }
 
 static notrace void nest_exit_handler(struct fprobe *fp, unsigned long ip,

samples/fprobe/fprobe_example.c

@@ -48,8 +48,8 @@ static void show_backtrace(void)
 	stack_trace_print(stacks, len, 24);
 }
 
-static void sample_entry_handler(struct fprobe *fp, unsigned long ip,
-				 struct pt_regs *regs, void *data)
+static int sample_entry_handler(struct fprobe *fp, unsigned long ip,
+				struct pt_regs *regs, void *data)
 {
 	if (use_trace)
 		/*
@@ -62,6 +62,7 @@ static void sample_entry_handler(struct fprobe *fp, unsigned long ip,
 	nhit++;
 	if (stackdump)
 		show_backtrace();
+	return 0;
 }
 
 static void sample_exit_handler(struct fprobe *fp, unsigned long ip, struct pt_regs *regs,