Re: [PATCH v1] perf parse-events: Avoid segv if PMU lookup fails for legacy cache terms

[Arnaldo Carvalho de Melo]

Em Tue, Jul 11, 2023 at 11:52:50PM -0700, Ian Rogers escreveu:
> libfuzzer found the following command could segv:
> ```
> $ perf stat -e cpu/L2,L2/ true
> ```
> This is because the L2 term rewrites the perf_event_attr type to
> PERF_TYPE_HW_CACHE which then fails the PMU lookup for the second
> legacy cache term.
> 
> The new failure is consistent with repeated hardware terms:
> ```
> $ perf stat -e cpu/L2,L2/ true
> event syntax error: 'cpu/L2,L2/'
>                             \___ Failed to find PMU for type 3
> 
> Initial error:
> event syntax error: 'cpu/L2,L2/'
>                             \___ Failed to find PMU for type 3
> Run 'perf list' for a list of valid events
> 
>  Usage: perf stat [<options>] [<command>]
> 
>     -e, --event <event>   event selector. use 'perf list' to list available events
> $ perf stat -e cpu/cycles,cycles/ true
> event syntax error: 'cpu/cycles,cycles/'
>                                 \___ Failed to find PMU for type 0
> 
> Initial error:
> event syntax error: 'cpu/cycles,cycles/'
>                                 \___ Failed to find PMU for type 0
> Run 'perf list' for a list of valid events
> 
>  Usage: perf stat [<options>] [<command>]
> 
>     -e, --event <event>   event selector. use 'perf list' to list available events
> ```

I added the Fixes as requested:

Fixes: 6fd1e5191591f9d5 ("perf parse-events: Support PMUs for legacy cache events")

Please check if the patch below helps a bit giving more info to the
user, but still a bit cryptic:

⬢[acme@toolbox perf-tools]$ perf stat -e cpu/L2,L2/ true
event syntax error: 'cpu/L2,L2/'
                            \___ Failed to find PMU for perf_event_attr.type 3 (PERF_TYPE_HW_CACHE)

Initial error:
event syntax error: 'cpu/L2,L2/'
                            \___ Failed to find PMU for perf_event_attr.type 3 (PERF_TYPE_HW_CACHE)
Run 'perf list' for a list of valid events

 Usage: perf stat [<options>] [<command>]

    -e, --event <event>   event selector. use 'perf list' to list available events
⬢[acme@toolbox perf-tools]$

And the other case is needs more patching, so better leave this for 6.6.


⬢[acme@toolbox perf-tools]$ perf stat -e cpu/cycles,cycles/ true
event syntax error: 'cpu/cycles,cycles/'
                                \___ Failed to find PMU for type 0

Initial error:
event syntax error: 'cpu/cycles,cycles/'
                                \___ Failed to find PMU for type 0
Run 'perf list' for a list of valid events

 Usage: perf stat [<options>] [<command>]

    -e, --event <event>   event selector. use 'perf list' to list available events
⬢[acme@toolbox perf-tools]$

- Arnaldo

diff --git a/tools/perf/util/evsel_fprintf.h b/tools/perf/util/evsel_fprintf.h
index c8a9fac2f2ddc0f2..044612774a962020 100644
--- a/tools/perf/util/evsel_fprintf.h
+++ b/tools/perf/util/evsel_fprintf.h
@@ -4,6 +4,7 @@
 
 #include <stdio.h>
 #include <stdbool.h>
+#include <linux/types.h>
 
 struct evsel;
 
@@ -45,6 +46,8 @@ int sample__fprintf_sym(struct perf_sample *sample, struct addr_location *al,
 
 typedef int (*attr__fprintf_f)(FILE *, const char *, const char *, void *);
 
+const char *stringify_perf_type_id(u64 value);
+
 int perf_event_attr__fprintf(FILE *fp, struct perf_event_attr *attr,
 			     attr__fprintf_f attr__fprintf, void *priv);
 #endif // __PERF_EVSEL_H
diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index acde097e327cce8c..8678469cf974070a 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -25,6 +25,7 @@
 #include "asm/bug.h"
 #include "util/parse-branch-options.h"
 #include "util/evsel_config.h"
+#include "util/evsel_fprintf.h"
 #include "util/event.h"
 #include "util/bpf-filter.h"
 #include "util/util.h"
@@ -1219,9 +1220,11 @@ static int config_term_pmu(struct perf_event_attr *attr,
 		if (!pmu) {
 			char *err_str;
 
-			if (asprintf(&err_str, "Failed to find PMU for type %d", attr->type) >= 0)
+			if (asprintf(&err_str, "Failed to find PMU for perf_event_attr.type %d (%s)", attr->type,
+				     stringify_perf_type_id(attr->type)) >= 0) {
 				parse_events_error__handle(err, term->err_term,
 							   err_str, /*help=*/NULL);
+			}
 			return -EINVAL;
 		}
 		if (perf_pmu__supports_legacy_cache(pmu)) {
diff --git a/tools/perf/util/perf_event_attr_fprintf.c b/tools/perf/util/perf_event_attr_fprintf.c
index 2247991451f3aa1b..ce97371eda027271 100644
--- a/tools/perf/util/perf_event_attr_fprintf.c
+++ b/tools/perf/util/perf_event_attr_fprintf.c
@@ -74,7 +74,7 @@ static void __p_read_format(char *buf, size_t size, u64 value)
 }
 
 #define ENUM_ID_TO_STR_CASE(x) case x: return (#x);
-static const char *stringify_perf_type_id(u64 value)
+const char *stringify_perf_type_id(u64 value)
 {
 	switch (value) {
 	ENUM_ID_TO_STR_CASE(PERF_TYPE_HARDWARE)