linux-kernel - [PATCH v1] perf parse-events: Fix parsing of >30kb event strings

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Message-ID: <20250905042643.1937122-1-irogers@google.com>
Date: Thu,  4 Sep 2025 21:26:43 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf parse-events: Fix parsing of >30kb event strings

Metrics may generate many particularly uncore event references. The
resulting event string may then be >32kb. The parse events lex is
using "%option reject" which stores backtracking state in a buffer
sized at roughtly 30kb. If the event string is larger than this then a
buffer overflow and typically a crash happens.

The need for "%option reject" was for BPF events which were removed in
commit 3d6dfae88917 ("perf parse-events: Remove BPF event
support"). As "%option reject" is both a memory and performance cost
let's remove it and fix the parsing case for event strings being over
~30kb.

Whilst cleaning up "%option reject" make the header files accurately
reflect functions used in the code and tidy up not requiring yywrap.

Measuring on the "PMU JSON event tests" a modest reduction of 0.41%
user time and 0.27% max resident size was observed. More importantly
this change fixes parsing large metrics and event strings.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/parse-events.l | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
index 2034590eb789..1eaa8dbc26d8 100644
--- a/tools/perf/util/parse-events.l
+++ b/tools/perf/util/parse-events.l
@@ -5,16 +5,14 @@
 %option stack
 %option bison-locations
 %option yylineno
-%option reject
+%option noyywrap

 %{
 #include <errno.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
 #include "parse-events.h"
 #include "parse-events-bison.h"
-#include "evsel.h"

 char *parse_events_get_text(yyscan_t yyscanner);
 YYSTYPE *parse_events_get_lval(yyscan_t yyscanner);
@@ -222,10 +220,6 @@ do {							\
 	yycolumn += yyleng;				\
 } while (0);

-#define USER_REJECT		\
-	yycolumn -= yyleng;	\
-	REJECT
-
 %}

 %x mem
@@ -423,8 +417,3 @@ r{num_raw_hex}		{ return str(yyscanner, PE_RAW); }
 .			{ }

 %%
-
-int parse_events_wrap(void *scanner __maybe_unused)
-{
-	return 1;
-}
-- 
2.51.0.355.g5224444f11-goog