linux-kernel - [BUGFIX PATCH] tracing/kprobes: Fix within_notrace

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Date:   Thu,  2 Aug 2018 16:50:48 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     rostedt@...dmis.org,
        Francis Deslauriers <francis.deslauriers@...icios.com>,
        peterz@...radead.org, Shuah Khan <shuah@...nel.org>
Cc:     mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
        linux-kernel@...r.kernel.org
Subject: [BUGFIX PATCH] tracing/kprobes: Fix within_notrace_func() to check only notrace functions

Fix within_notrace_func() to check only notrace functions
and to ignore the kprobe-event which can not solve symbol
address.

within_notrace_func() returns true if the given kprobe events
probe point seems like out-of-range. But that is not correct
place to check it, it should be done in kprobes afterwards.

kprobe-events allows user to define a probe point on "currently
unloaded module" so that it can trace the event while module
load. In this case, user will put a probe on a symbol which
is not in kallsyms yet and it hits the within_notrace_func().
In the result, kprobe-events always refuses if user defines
a probe on "currenly unloaded module".

Fixes: commit 45408c4f9250 ("tracing: kprobes: Prohibit probing on notrace function")
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_kprobe.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index deeb03ae21e1..2e13f77b9a37 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -88,6 +88,7 @@ static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
 	return nhit;
 }
 
+/* Return 0 if it fails to find the symbol address */
 static nokprobe_inline
 unsigned long trace_kprobe_address(struct trace_kprobe *tk)
 {
@@ -96,7 +97,8 @@ unsigned long trace_kprobe_address(struct trace_kprobe *tk)
 	if (tk->symbol) {
 		addr = (unsigned long)
 			kallsyms_lookup_name(trace_kprobe_symbol(tk));
-		addr += tk->rp.kp.offset;
+		if (addr)
+			addr += tk->rp.kp.offset;
 	} else {
 		addr = (unsigned long)tk->rp.kp.addr;
 	}
@@ -519,8 +521,8 @@ static bool within_notrace_func(struct trace_kprobe *tk)
 	unsigned long offset, size, addr;
 
 	addr = trace_kprobe_address(tk);
-	if (!kallsyms_lookup_size_offset(addr, &size, &offset))
-		return true;	/* Out of range. */
+	if (!addr || !kallsyms_lookup_size_offset(addr, &size, &offset))
+		return false;
 
 	return !ftrace_location_range(addr - offset, addr - offset + size);
 }