linux-kernel - [PATCH v3 3/3] trace: print address if symbol not found

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Date:   Wed, 20 Dec 2017 08:39:24 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     kernel-hardening@...ts.openwall.com
Cc:     "Tobin C. Harding" <me@...in.cc>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-kernel@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>,
        Joe Perches <joe@...ches.com>
Subject: [PATCH v3 3/3] trace: print address if symbol not found

Fixes behaviour modified by: commit 40eee173a35e ("kallsyms: don't leak
address when symbol not found")

Previous patch changed behaviour of kallsyms function sprint_symbol() to
return an error code instead of printing the address if a symbol was not
found. Ftrace relies on the original behaviour. We should not break
tracing when applying the previous patch. We can maintain the original
behaviour by checking the return code on calls to sprint_symbol() and
friends.

Check return code and print actual address on error (i.e symbol not
found).

Signed-off-by: Tobin C. Harding <me@...in.cc>
---
 kernel/trace/trace.h             | 24 ++++++++++++++++++++++++
 kernel/trace/trace_events_hist.c |  6 +++---
 kernel/trace/trace_output.c      |  2 +-
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 2a6d0325a761..881b1a577d75 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1814,4 +1814,28 @@ static inline void trace_event_eval_update(struct trace_eval_map **map, int len)
 
 extern struct trace_iterator *tracepoint_print_iter;
 
+static inline int
+trace_sprint_symbol(char *buffer, unsigned long address)
+{
+	int ret;
+
+	ret = sprint_symbol(buffer, address);
+	if (ret == -1)
+		ret = sprintf(buffer, "0x%lx", address);
+
+	return ret;
+}
+
+static inline int
+trace_sprint_symbol_no_offset(char *buffer, unsigned long address)
+{
+	int ret;
+
+	ret = sprint_symbol_no_offset(buffer, address);
+	if (ret == -1)
+		ret = sprintf(buffer, "0x%lx", address);
+
+	return ret;
+}
+
 #endif /* _LINUX_KERNEL_TRACE_H */
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 1e1558c99d56..ca523327c058 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -982,7 +982,7 @@ static void hist_trigger_stacktrace_print(struct seq_file *m,
 			return;
 
 		seq_printf(m, "%*c", 1 + spaces, ' ');
-		sprint_symbol(str, stacktrace_entries[i]);
+		trace_sprint_symbol(str, stacktrace_entries[i]);
 		seq_printf(m, "%s\n", str);
 	}
 }
@@ -1014,12 +1014,12 @@ hist_trigger_entry_print(struct seq_file *m,
 			seq_printf(m, "%s: %llx", field_name, uval);
 		} else if (key_field->flags & HIST_FIELD_FL_SYM) {
 			uval = *(u64 *)(key + key_field->offset);
-			sprint_symbol_no_offset(str, uval);
+			trace_sprint_symbol_no_offset(str, uval);
 			seq_printf(m, "%s: [%llx] %-45s", field_name,
 				   uval, str);
 		} else if (key_field->flags & HIST_FIELD_FL_SYM_OFFSET) {
 			uval = *(u64 *)(key + key_field->offset);
-			sprint_symbol(str, uval);
+			trace_sprint_symbol(str, uval);
 			seq_printf(m, "%s: [%llx] %-55s", field_name,
 				   uval, str);
 		} else if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 90db994ac900..f3c3a0a60f72 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -365,7 +365,7 @@ seq_print_sym_offset(struct trace_seq *s, const char *fmt,
 #ifdef CONFIG_KALLSYMS
 	const char *name;
 
-	sprint_symbol(str, address);
+	trace_sprint_symbol(str, address);
 	name = kretprobed(str);
 
 	if (name && strlen(name)) {
-- 
2.7.4