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perf parse-events: Fix big-endian 'overwrite' by writing correct union member

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The "Read backward ring buffer" test crashes on big-endian (e.g. s390x)
due to a NULL dereference when the backward mmap path isn't enabled.

Reproducer:
  # ./perf test -F 'Read backward ring buffer'
  Segmentation fault (core dumped)
  # uname -m
  s390x
  #

Root cause:
get_config_terms() stores into evsel_config_term::val.val (u64) while later
code reads boolean fields such as evsel_config_term::val.overwrite.
On big-endian the 1-byte boolean is left-aligned, so writing
evsel_config_term::val.val = 1 is read back as
evsel_config_term::val.overwrite = 0,
leaving backward mmap disabled and a NULL map being used.

Store values in the union member that matches the term type, e.g.:
  /* for OVERWRITE */
  new_term->val.overwrite = 1;  /* not new_term->val.val = 1 */
to fix this. Improve add_config_term() and add two more parameters for
string and value. Function add_config_term() now creates a complete node
element of type evsel_config_term and handles all evsel_config_term::val
union members.

Impact:
Enables backward mmap on big-endian and prevents the crash.
No change on little-endian.

Output after:
 # ./perf test -Fv 44
 --- start ---
 Using CPUID IBM,9175,705,ME1,3.8,002f
 mmap size 1052672B
 mmap size 8192B
 ---- end ----
 44: Read backward ring buffer                         : Ok
 #

Fixes: 159ca97cd9 ("perf parse-events: Refactor get_config_terms() to remove macros")
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@linaro.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Thomas Richter
2026-02-17 14:14:56 +01:00
committed by Arnaldo Carvalho de Melo
parent 8dd1d9a335
commit 72a8b9c060
1 changed files with 65 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

82
tools/perf/util/parse-events.c
View File

@@ -1117,7 +1117,7 @@ static int config_attr(struct perf_event_attr *attr,
static struct evsel_config_term *add_config_term(enum evsel_term_type type,
struct list_head *head_terms,
bool weak)
bool weak, char *str, u64 val)
{
struct evsel_config_term *t;
@@ -1128,8 +1128,62 @@ static struct evsel_config_term *add_config_term(enum evsel_term_type type,
INIT_LIST_HEAD(&t->list);
t->type = type;
t->weak = weak;
list_add_tail(&t->list, head_terms);
switch (type) {
case EVSEL__CONFIG_TERM_PERIOD:
case EVSEL__CONFIG_TERM_FREQ:
case EVSEL__CONFIG_TERM_STACK_USER:
case EVSEL__CONFIG_TERM_USR_CHG_CONFIG:
case EVSEL__CONFIG_TERM_USR_CHG_CONFIG1:
case EVSEL__CONFIG_TERM_USR_CHG_CONFIG2:
case EVSEL__CONFIG_TERM_USR_CHG_CONFIG3:
case EVSEL__CONFIG_TERM_USR_CHG_CONFIG4:
t->val.val = val;
break;
case EVSEL__CONFIG_TERM_TIME:
t->val.time = val;
break;
case EVSEL__CONFIG_TERM_INHERIT:
t->val.inherit = val;
break;
case EVSEL__CONFIG_TERM_OVERWRITE:
t->val.overwrite = val;
break;
case EVSEL__CONFIG_TERM_MAX_STACK:
t->val.max_stack = val;
break;
case EVSEL__CONFIG_TERM_MAX_EVENTS:
t->val.max_events = val;
break;
case EVSEL__CONFIG_TERM_PERCORE:
t->val.percore = val;
break;
case EVSEL__CONFIG_TERM_AUX_OUTPUT:
t->val.aux_output = val;
break;
case EVSEL__CONFIG_TERM_AUX_SAMPLE_SIZE:
t->val.aux_sample_size = val;
break;
case EVSEL__CONFIG_TERM_CALLGRAPH:
case EVSEL__CONFIG_TERM_BRANCH:
case EVSEL__CONFIG_TERM_DRV_CFG:
case EVSEL__CONFIG_TERM_RATIO_TO_PREV:
case EVSEL__CONFIG_TERM_AUX_ACTION:
if (str) {
t->val.str = strdup(str);
if (!t->val.str) {
zfree(&t);
return NULL;
}
t->free_str = true;
}
break;
default:
t->val.val = val;
break;
}
list_add_tail(&t->list, head_terms);
return t;
}
@@ -1142,7 +1196,7 @@ static int get_config_terms(const struct parse_events_terms *head_config,
struct evsel_config_term *new_term;
enum evsel_term_type new_type;
bool str_type = false;
u64 val;
u64 val = 0;
switch (term->type_term) {
case PARSE_EVENTS__TERM_TYPE_SAMPLE_PERIOD:
@@ -1234,20 +1288,15 @@ static int get_config_terms(const struct parse_events_terms *head_config,
continue;
}
new_term = add_config_term(new_type, head_terms, term->weak);
/*
* Note: Members evsel_config_term::val and
* parse_events_term::val are unions and endianness needs
* to be taken into account when changing such union members.
*/
new_term = add_config_term(new_type, head_terms, term->weak,
str_type ? term->val.str : NULL, val);
if (!new_term)
return -ENOMEM;
if (str_type) {
new_term->val.str = strdup(term->val.str);
if (!new_term->val.str) {
zfree(&new_term);
return -ENOMEM;
}
new_term->free_str = true;
} else {
new_term->val.val = val;
}
}
return 0;
}
@@ -1277,10 +1326,9 @@ static int add_cfg_chg(const struct perf_pmu *pmu,
if (bits) {
struct evsel_config_term *new_term;
new_term = add_config_term(new_term_type, head_terms, false);
new_term = add_config_term(new_term_type, head_terms, false, NULL, bits);
if (!new_term)
return -ENOMEM;
new_term->val.cfg_chg = bits;
}
return 0;