[PATCH v1 0/4] perf: Fix and optimize maps parsing, boundaries, and bounds safety

[PATCH v1 0/4] perf: Fix and optimize maps parsing, boundaries, and bounds safety

[Ian Rogers]

It turns out that PATH_MAX is respected by system calls but isn't
respected by file paths in /proc/pid/maps and /proc/pid/smaps. In the
kernel "//toolong" is placed in the filename of mmap/mmap2 events
where the filename is longer than PATH_MAX, do the same in the
mmap/mmap2 synthesis code to avoid overrunning the event buffer. With
Gemini's help try to address other correctness and overrun issues.

Ian Rogers (4):
  perf find-map: Remove PATH_MAX 128-byte stack array restriction
  perf synthetic-events: Fix line synchronization, bounds, and
    truncation bugs in proc maps reader
  perf synthetic-events: Fix bounds, stale state, and misc flags in
    kernel module synthesis
  perf synthetic-events: Fix bounds and union member access in mmap2
    build_id synthesis

 tools/perf/util/find-map.c         |  11 +-
 tools/perf/util/synthetic-events.c | 271 ++++++++++++++++++++---------
 2 files changed, 196 insertions(+), 86 deletions(-)

-- 
2.55.0.229.g6434b31f56-goog

[PATCH v1 1/4] perf find-map: Remove PATH_MAX 128-byte stack array restriction

[Ian Rogers]

Use getline() to dynamically allocate the required line buffer for maps
parsing, guaranteeing bounds safety and preventing buffer overruns.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/find-map.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
index 7b2300588ece..4d740b32814f 100644
--- a/tools/perf/util/find-map.c
+++ b/tools/perf/util/find-map.c
@@ -1,8 +1,14 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
 static int find_map(void **start, void **end, const char *name)
 {
 	FILE *maps;
-	char line[128];
+	char *line = NULL;
+	size_t len = 0;
+	ssize_t read_ret;
 	int found = 0;
 
 	maps = fopen("/proc/self/maps", "r");
@@ -11,7 +17,7 @@ static int find_map(void **start, void **end, const char *name)
 		return -1;
 	}
 
-	while (!found && fgets(line, sizeof(line), maps)) {
+	while (!found && (read_ret = getline(&line, &len, maps)) != -1) {
 		int m = -1;
 
 		/* We care only about private r-x mappings. */
@@ -25,6 +31,7 @@ static int find_map(void **start, void **end, const char *name)
 			found = 1;
 	}
 
+	free(line);
 	fclose(maps);
 	return !found;
 }
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v1 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[Ian Rogers]

Fix critical logic and boundary bugs in read_proc_maps_line() and caller.
Ensure any mid-line hex/dec/char parsing failure invokes io__drain_line()
to preserve line synchronization for subsequent map entries. Replace the
truncation bug (which improperly cleared over-length pathnames to an empty
string) with the kernel's standard '//toolong' fallback literal, and clamp
and pad structure size boundaries safely.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 183 ++++++++++++++++++++---------
 1 file changed, 127 insertions(+), 56 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index b75f9dcf4dbf..9161dc728e6e 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -291,6 +291,15 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
 	return 0;
 }
 
+static void io__drain_line(struct io *io)
+{
+	int ch;
+
+	do {
+		ch = io__get_char(io);
+	} while (ch >= 0 && ch != '\n');
+}
+
 static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 				u32 *prot, u32 *flags, __u64 *offset,
 				u32 *maj, u32 *min,
@@ -299,69 +308,121 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 {
 	__u64 temp;
 	int ch;
-	char *start_pathname = pathname;
+	size_t written = 0;
+	bool overflowed = false;
 
-	if (io__get_hex(io, start) != '-')
+	if (io__get_hex(io, start) != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
-	if (io__get_hex(io, end) != ' ')
+	}
+	if (io__get_hex(io, end) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 
 	/* map protection and flags bits */
 	*prot = 0;
 	ch = io__get_char(io);
 	if (ch == 'r')
 		*prot |= PROT_READ;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'w')
 		*prot |= PROT_WRITE;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'x')
 		*prot |= PROT_EXEC;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 's')
 		*flags = MAP_SHARED;
 	else if (ch == 'p')
 		*flags = MAP_PRIVATE;
-	else
+	else {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
-	if (io__get_char(io) != ' ')
+	}
+	if (io__get_char(io) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 
-	if (io__get_hex(io, offset) != ' ')
+	if (io__get_hex(io, offset) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 
-	if (io__get_hex(io, &temp) != ':')
+	if (io__get_hex(io, &temp) != ':') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	*maj = temp;
-	if (io__get_hex(io, &temp) != ' ')
+	if (io__get_hex(io, &temp) != ' ') {
+		if (!io->eof)
+			io__drain_line(io);
 		return false;
+	}
 	*min = temp;
 
 	ch = io__get_dec(io, inode);
 	if (ch != ' ') {
-		*pathname = '\0';
-		return ch == '\n';
+		if (ch == '\n') {
+			pathname[0] = '\0';
+			return true;
+		}
+		if (!io->eof)
+			io__drain_line(io);
+		return false;
 	}
+
 	do {
 		ch = io__get_char(io);
 	} while (ch == ' ');
+
 	while (true) {
-		if (ch < 0)
-			return false;
-		if (ch == '\0' || ch == '\n' ||
-		    (pathname + 1 - start_pathname) >= pathname_size) {
-			*pathname = '\0';
-			return true;
+		if (ch < 0) {
+			if (overflowed) {
+				strlcpy(pathname, "//toolong", pathname_size);
+				return true;
+			}
+			pathname[written] = '\0';
+			return written > 0;
 		}
-		*pathname++ = ch;
+		if (ch == '\0' || ch == '\n')
+			break;
+
+		if (written < (size_t)pathname_size - 1)
+			pathname[written++] = (char)ch;
+		else
+			overflowed = true;
 		ch = io__get_char(io);
 	}
+
+	if (overflowed)
+		strlcpy(pathname, "//toolong", pathname_size);
+	else
+		pathname[written] = '\0';
+
+	return true;
 }
 
 static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
@@ -457,29 +518,25 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 	}
 	io__init(&io, io.fd, bf, sizeof(bf));
 
-	event->header.type = PERF_RECORD_MMAP2;
 	t = rdclock();
 
 	while (!io.eof) {
 		static const char anonstr[] = "//anon";
 		size_t size, aligned_size;
-
-		/* ensure null termination since stack will be reused. */
-		event->mmap2.filename[0] = '\0';
+		__u64 start, end, pgoff, ino;
+		u32 prot, flags, maj, min;
 
 		/* 00400000-0040c000 r-xp 00000000 fd:01 41038  /bin/cat */
-		if (!read_proc_maps_line(&io,
-					&event->mmap2.start,
-					&event->mmap2.len,
-					&event->mmap2.prot,
-					&event->mmap2.flags,
-					&event->mmap2.pgoff,
-					&event->mmap2.maj,
-					&event->mmap2.min,
-					&event->mmap2.ino,
-					sizeof(event->mmap2.filename),
-					event->mmap2.filename))
+		/* Read directly into event->mmap2.filename! */
+		if (!read_proc_maps_line(&io, &start, &end,
+					 &prot, &flags, &pgoff,
+					 &maj, &min, &ino,
+					 sizeof(event->mmap2.filename),
+					 event->mmap2.filename)) {
+			if (io.eof)
+				break;
 			continue;
+		}
 
 		if ((rdclock() - t) > timeout) {
 			pr_warning("Reading %s/proc/%d/task/%d/maps time out. "
@@ -487,50 +544,64 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 				   "the time limit by --proc-map-timeout\n",
 				   machine->root_dir, pid, pid);
 			truncation = true;
-			goto out;
 		}
 
-		event->mmap2.ino_generation = 0;
+		if (!strcmp(event->mmap2.filename, ""))
+			strcpy(event->mmap2.filename, anonstr);
+
+		if (hugetlbfs_mnt_len &&
+		    !strncmp(event->mmap2.filename, hugetlbfs_mnt, hugetlbfs_mnt_len)) {
+			strcpy(event->mmap2.filename, anonstr);
+			flags |= MAP_HUGETLB;
+		}
+
+		size = strlen(event->mmap2.filename) + 1;
+		aligned_size = PERF_ALIGN(size, sizeof(u64));
+
+		event->mmap2.header.type = PERF_RECORD_MMAP2;
 
 		/*
-		 * Just like the kernel, see __perf_event_mmap in kernel/perf_event.c
+		 * Just like the kernel, see perf_misc_flags() in
+		 * kernel/events/core.c
 		 */
 		if (machine__is_host(machine))
 			event->header.misc = PERF_RECORD_MISC_USER;
 		else
 			event->header.misc = PERF_RECORD_MISC_GUEST_USER;
 
-		if ((event->mmap2.prot & PROT_EXEC) == 0) {
-			if (!mmap_data || (event->mmap2.prot & PROT_READ) == 0)
+		if ((prot & PROT_EXEC) == 0) {
+			if (!mmap_data || (prot & PROT_READ) == 0) {
+				if (truncation)
+					break;
 				continue;
+			}
 
 			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
 		}
 
-out:
 		if (truncation)
 			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;
 
-		if (!strcmp(event->mmap2.filename, ""))
-			strcpy(event->mmap2.filename, anonstr);
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
 
-		if (hugetlbfs_mnt_len &&
-		    !strncmp(event->mmap2.filename, hugetlbfs_mnt,
-			     hugetlbfs_mnt_len)) {
-			strcpy(event->mmap2.filename, anonstr);
-			event->mmap2.flags |= MAP_HUGETLB;
-		}
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + machine->id_hdr_size);
 
-		size = strlen(event->mmap2.filename) + 1;
-		aligned_size = PERF_ALIGN(size, sizeof(u64));
-		event->mmap2.len -= event->mmap.start;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - aligned_size));
-		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
-			(aligned_size - size));
 		event->mmap2.header.size += machine->id_hdr_size;
+		event->mmap2.start = start;
+		event->mmap2.len = end - start;
+		event->mmap2.pgoff = pgoff;
+		event->mmap2.maj = maj;
+		event->mmap2.min = min;
+		event->mmap2.ino = ino;
+		event->mmap2.ino_generation = 0;
 		event->mmap2.pid = tgid;
 		event->mmap2.tid = pid;
+		event->mmap2.prot = prot;
+		event->mmap2.flags = flags;
 
 		if (!symbol_conf.no_buildid_mmap2)
 			perf_record_mmap2__read_build_id(&event->mmap2, machine, false);
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v1 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

[Ian Rogers]

Fix potential buffer overruns in perf_event__synthesize_modules_maps_cb()
by safely clamping long DSO names to the mmap/mmap2 filename boundaries.
Explicitly assign and clear the misc flags and union padding across all
iterations to prevent stale Build-ID state from leaking between module
synthesis events.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 70 +++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 9161dc728e6e..aab958cb3bc5 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -748,6 +748,7 @@ struct perf_event__synthesize_modules_maps_cb_args {
 	perf_event__handler_t process;
 	struct machine *machine;
 	union perf_event *event;
+	u16 misc;
 };
 
 static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
@@ -755,49 +756,78 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
 	struct perf_event__synthesize_modules_maps_cb_args *args = data;
 	union perf_event *event = args->event;
 	struct dso *dso;
-	size_t size;
+	size_t size, aligned_size;
+	int rc = 0;
 
 	if (!__map__is_kmodule(map))
 		return 0;
 
 	dso = map__dso(map);
 	if (!symbol_conf.no_buildid_mmap2) {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap2.filename))
+			size = sizeof(event->mmap2.filename) - 1;
+
+		strlcpy(event->mmap2.filename, long_name,
+			sizeof(event->mmap2.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap2.header.type = PERF_RECORD_MMAP2;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - size));
-		memset(event->mmap2.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap2.header.misc = args->misc;
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap2.header.size += args->machine->id_hdr_size;
 		event->mmap2.start = map__start(map);
 		event->mmap2.len   = map__size(map);
 		event->mmap2.pid   = args->machine->pid;
 
-		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
-
-		/* Clear stale build ID from previous module iteration */
+		/* Clear stale build ID and entire union from previous module iteration */
 		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
 		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
 		event->mmap2.build_id_size = 0;
+		event->mmap2.__reserved_1 = 0;
+		event->mmap2.__reserved_2 = 0;
 
 		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
 	} else {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap.filename))
+			size = sizeof(event->mmap.filename) - 1;
+
+		strlcpy(event->mmap.filename, long_name,
+			sizeof(event->mmap.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap.header.type = PERF_RECORD_MMAP;
-		event->mmap.header.size = (sizeof(event->mmap) -
-					(sizeof(event->mmap.filename) - size));
-		memset(event->mmap.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap.header.misc = args->misc;
+		event->mmap.header.size =
+			offsetof(struct perf_record_mmap, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap.header.size += args->machine->id_hdr_size;
 		event->mmap.start = map__start(map);
 		event->mmap.len   = map__size(map);
 		event->mmap.pid   = args->machine->pid;
-
-		memcpy(event->mmap.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
 	}
 
 	if (perf_tool__process_synth_event(args->tool, event, args->machine, args->process) != 0)
-		return -1;
+		rc = -1;
 
-	return 0;
+	return rc;
 }
 
 int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__handler_t process,
@@ -822,13 +852,13 @@ int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__han
 	}
 
 	/*
-	 * kernel uses 0 for user space maps, see kernel/perf_event.c
-	 * __perf_event_mmap
+	 * Just like the kernel, see perf_misc_flags() in
+	 * kernel/events/core.c
 	 */
 	if (machine__is_host(machine))
-		args.event->header.misc = PERF_RECORD_MISC_KERNEL;
+		args.misc = PERF_RECORD_MISC_KERNEL;
 	else
-		args.event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
+		args.misc = PERF_RECORD_MISC_GUEST_KERNEL;
 
 	rc = maps__for_each_map(maps, perf_event__synthesize_modules_maps_cb, &args);
 
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v1 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

[Ian Rogers]

Fix a critical logic bug in perf_event__synthesize_mmap2_build_id() where
the wrong union member structure size and offset boundaries were utilized.
Safely calculate and clamp maximum filename length to guarantee absolute
stack boundary protections for ID sample trailers, and remove void-pointer
arithmetic to meet strict standard C compliance.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index aab958cb3bc5..cb5b659822f5 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -2441,13 +2441,16 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 	size_t filename_len = strlen(filename);
 	size_t ev_len;
 	u64 sample_type = sample->evsel ? sample->evsel->core.attr.sample_type : 0;
-	void *array;
+	void *array = &ev;
 	int ret;
+	size_t max_filename_len;
 
-	if (filename_len >= sizeof(ev.mmap2.filename))
-		return -EINVAL;
+	max_filename_len = sizeof(ev.mmap2.filename) - (MAX_ID_HDR_ENTRIES * sizeof(__u64));
 
-	ev_len = sizeof(ev.mmap2) - sizeof(ev.mmap2.filename) + filename_len + 1;
+	if (filename_len > max_filename_len)
+		filename_len = max_filename_len;
+
+	ev_len = offsetof(struct perf_record_mmap2, filename) + filename_len + 1;
 	ev_len = PERF_ALIGN(ev_len, sizeof(u64));
 
 	if (ev_len + MAX_ID_HDR_ENTRIES * sizeof(__u64) > sizeof(ev))
@@ -2467,16 +2470,15 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 
 	ev.mmap2.build_id_size = bid->size;
 	if (ev.mmap2.build_id_size > sizeof(ev.mmap2.build_id))
-		ev.build_id.size = sizeof(ev.mmap2.build_id);
+		ev.mmap2.build_id_size = sizeof(ev.mmap2.build_id);
 	memcpy(ev.mmap2.build_id, bid->data, ev.mmap2.build_id_size);
 
 	ev.mmap2.prot = prot;
 	ev.mmap2.flags = flags;
 
-	memcpy(ev.mmap2.filename, filename, min(strlen(filename), sizeof(ev.mmap.filename)));
+	strlcpy(ev.mmap2.filename, filename, filename_len + 1);
 
-	array = &ev;
-	array += ev.header.size;
+	array = (void *)((char *)&ev + ev.header.size);
 	ret = perf_event__synthesize_id_sample(array, sample_type, sample);
 	if (ret < 0)
 		return ret;
-- 
2.55.0.229.g6434b31f56-goog

Re: [PATCH v1 1/4] perf find-map: Remove PATH_MAX 128-byte stack array restriction

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The `read_ret` variable is assigned the result of `getline()` but is never subsequently used, which triggers a `-Wunused-but-set-variable` compilation error.
--

--- Patch [1]: [PATCH v1 1/4] perf find-map: Remove PATH_MAX 128-byte stack array restriction ---
commit 9da3c5d9150546a40fb376c8547c0725fc587af7
Author: Ian Rogers <irogers@google.com>
perf find-map: Remove PATH_MAX 128-byte stack array restriction

This commit updates the find_map function to dynamically allocate the 
line buffer using getline. This prevents potential buffer overruns 
associated with the previous 128-byte stack array limitation.

> diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
> index 7b2300588ece0..4d740b32814f8 100644
> --- a/tools/perf/util/find-map.c
> +++ b/tools/perf/util/find-map.c
[ ... ]
> @@ -1,8 +1,14 @@
>  // SPDX-License-Identifier: GPL-2.0
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +
>  static int find_map(void **start, void **end, const char *name)
>  {
>  	FILE *maps;
> -	char line[128];
> +	char *line = NULL;
> +	size_t len = 0;
> +	ssize_t read_ret;
>  	int found = 0;
>  
>  	maps = fopen("/proc/self/maps", "r");
> @@ -11,7 +17,7 @@ static int find_map(void **start, void **end, const char *name)
>  		return -1;
>  	}
>  
> -	while (!found && fgets(line, sizeof(line), maps)) {
> +	while (!found && (read_ret = getline(&line, &len, maps)) != -1) {

[Severity: Low]
Does this leave the read_ret variable set but never used?

Because perf is typically built with -Werror, this unused assignment
triggers a -Wunused-but-set-variable compiler warning which gets promoted
to a build failure. 

Could the read_ret variable be removed and the loop condition simplified to 
just evaluate getline(&line, &len, maps) != -1 directly?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260720175455.3645946-1-irogers@google.com?part=1

Re: [PATCH v1 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Error recovery via `io__drain_line()` incorrectly consumes and discards the next valid map entry if a parsing failure occurs due to a premature newline character.
- [Medium] The PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT flag is silently dropped if the truncation timeout triggers on a map entry that fails the PROT_EXEC/mmap_data filters.
--

--- Patch [2]: [PATCH v1 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader ---
commit 21e332ccbb14a1f50a59ea36a8f2a24a05ff7df8
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

This commit addresses logic and boundary bugs in read_proc_maps_line() and its
caller. It ensures that mid-line parsing failures invoke io__drain_line() to
preserve synchronization and replaces truncation bugs with a standard fallback
literal.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 5307d707711d8..723b7323c06d9 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -291,6 +291,15 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
>  	return 0;
>  }
>  
> +static void io__drain_line(struct io *io)
> +{
> +	int ch;
> +
> +	do {
> +		ch = io__get_char(io);
> +	} while (ch >= 0 && ch != '\n');
> +}
> +
>  static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
>  				u32 *prot, u32 *flags, __u64 *offset,
>  				u32 *maj, u32 *min,
> @@ -299,69 +308,121 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
>  {
>  	__u64 temp;
>  	int ch;
> -	char *start_pathname = pathname;
> +	size_t written = 0;
> +	bool overflowed = false;
>  
> -	if (io__get_hex(io, start) != '-')
> +	if (io__get_hex(io, start) != '-') {
> +		if (!io->eof)
> +			io__drain_line(io);

[Severity: High]
If a parser like io__get_hex() or io__get_char() fails because it encounters a
premature newline character, does calling io__drain_line() here unintentionally
consume and discard the next valid map entry?

Since the newline character for the malformed line would have already been
consumed by the parser, it appears io__drain_line() might read until the end
of the subsequent line, causing it to be skipped.

> +		return false;
> +	}

[ ... ]

> @@ -487,50 +544,64 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,

[ ... ]

> -		if ((event->mmap2.prot & PROT_EXEC) == 0) {
> -			if (!mmap_data || (event->mmap2.prot & PROT_READ) == 0)
> +		if ((prot & PROT_EXEC) == 0) {
> +			if (!mmap_data || (prot & PROT_READ) == 0) {
> +				if (truncation)
> +					break;

[Severity: Medium]
When the truncation timeout triggers on a map entry that fails the PROT_EXEC
or mmap_data filters, does this break prevent the timeout flag
(PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT) from being set and emitted?

By breaking out of the loop early here, it seems the code bypasses both the
PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT assignment and the call to
perf_tool__process_synth_event(), which might leave analysis tools unaware
that the data stream was truncated.

>  				continue;
> +			}
>  
>  			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
>  		}
>  
> -out:
>  		if (truncation)
>  			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260720175455.3645946-1-irogers@google.com?part=2

Re: [PATCH v1 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly introduced `max_filename_len` clamping mechanism fails to prevent `-E2BIG` errors for long filenames because it does not account for alignment padding and the NUL byte.
--

--- Patch [4]: [PATCH v1 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis ---
commit 2f96e2c59cef660df31770f938440d336831e6e7
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

Fix a critical logic bug in perf_event__synthesize_mmap2_build_id() where
the wrong union member structure size and offset boundaries were utilized.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 043f902f1bd2e..3a4030835a320 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -2441,13 +2441,16 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
>  	size_t filename_len = strlen(filename);
>  	size_t ev_len;
>  	u64 sample_type = sample->evsel ? sample->evsel->core.attr.sample_type : 0;
> -	void *array;
> +	void *array = &ev;
>  	int ret;
> +	size_t max_filename_len;
>  
> -	if (filename_len >= sizeof(ev.mmap2.filename))
> -		return -EINVAL;
> +	max_filename_len = sizeof(ev.mmap2.filename) - (MAX_ID_HDR_ENTRIES * sizeof(__u64));
>  
> -	ev_len = sizeof(ev.mmap2) - sizeof(ev.mmap2.filename) + filename_len + 1;
> +	if (filename_len > max_filename_len)
> +		filename_len = max_filename_len;
> +
> +	ev_len = offsetof(struct perf_record_mmap2, filename) + filename_len + 1;
>  	ev_len = PERF_ALIGN(ev_len, sizeof(u64));
>  
>  	if (ev_len + MAX_ID_HDR_ENTRIES * sizeof(__u64) > sizeof(ev))
>  		return -E2BIG;

[Severity: Medium]
Does this clamping logic fail to prevent -E2BIG errors for very long
filenames?

If filename_len is clamped to max_filename_len (4048 bytes), ev_len is
subsequently calculated as offsetof(struct perf_record_mmap2, filename) +
4048 + 1 (for the NUL byte), which equals 4129.

PERF_ALIGN(4129, sizeof(u64)) aligns this up to 4136.

When checking if the padded length plus the ID header trailer exceeds the
maximum event size:
4136 + 48 = 4184, which exceeds sizeof(ev) (4176).

This causes the function to return -E2BIG instead of successfully truncating
and processing the event. Should max_filename_len account for the NUL byte
and the 8-byte alignment padding to ensure the clamped size fits within
the boundaries?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260720175455.3645946-1-irogers@google.com?part=4

[PATCH v2 0/4] perf: Fix and optimize maps parsing, boundaries, and bounds safety

[Ian Rogers]

It turns out that PATH_MAX is respected by system calls but isn't
respected by file paths in /proc/pid/maps and /proc/pid/smaps. In the
kernel "//toolong" is placed in the filename of mmap/mmap2 events
where the filename is longer than PATH_MAX, do the same in the
mmap/mmap2 synthesis code to avoid overrunning the event buffer. With
Gemini's help try to address other correctness and overrun issues.

V2 addresses the following Sashiko review feedback:
- Corrects read_proc_maps_line() and io__drain_line() to safely handle
  already consumed newlines, preventing valid map data from being skipped.
- Restores the early exit block for timeouts so the TIMEOUT flag is
  always emitted to tools.
- Removes an unused assignment to avoid promoting warnings to build errors.
- Clarifies and dynamically computes the maximum filename length boundaries
  using offsetof() to prevent E2BIG errors regardless of struct layout.

Ian Rogers (4):
  perf find-map: Remove PATH_MAX 128-byte stack array restriction
  perf synthetic-events: Fix line synchronization, bounds, and
    truncation bugs in proc maps reader
  perf synthetic-events: Fix bounds, stale state, and misc flags in
    kernel module synthesis
  perf synthetic-events: Fix bounds and union member access in mmap2
    build_id synthesis

 tools/perf/util/find-map.c         |  10 +-
 tools/perf/util/synthetic-events.c | 287 ++++++++++++++++++++---------
 2 files changed, 207 insertions(+), 90 deletions(-)

-- 
2.55.0.229.g6434b31f56-goog

[PATCH v2 1/4] perf find-map: Remove PATH_MAX 128-byte stack array restriction

[Ian Rogers]

Use getline() to dynamically allocate the required line buffer for maps
parsing, guaranteeing bounds safety and avoiding compiler warnings
by evaluating the return value in the loop condition directly.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/find-map.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
index 7b2300588ece..bba511795a69 100644
--- a/tools/perf/util/find-map.c
+++ b/tools/perf/util/find-map.c
@@ -1,8 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
 static int find_map(void **start, void **end, const char *name)
 {
 	FILE *maps;
-	char line[128];
+	char *line = NULL;
+	size_t len = 0;
 	int found = 0;
 
 	maps = fopen("/proc/self/maps", "r");
@@ -11,7 +16,7 @@ static int find_map(void **start, void **end, const char *name)
 		return -1;
 	}
 
-	while (!found && fgets(line, sizeof(line), maps)) {
+	while (!found && getline(&line, &len, maps) != -1) {
 		int m = -1;
 
 		/* We care only about private r-x mappings. */
@@ -25,6 +30,7 @@ static int find_map(void **start, void **end, const char *name)
 			found = 1;
 	}
 
+	free(line);
 	fclose(maps);
 	return !found;
 }
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v2 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[Ian Rogers]

Fix critical logic and boundary bugs in read_proc_maps_line() and caller.
Ensure any mid-line hex/dec/char parsing failure invokes io__drain_line()
safely, ignoring already-consumed newlines to preserve synchronization
for subsequent map entries. Use standard '//toolong' fallback literal
for over-length pathnames, and emit timeout flags for truncated entries
securely via goto out;.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 197 ++++++++++++++++++++---------
 1 file changed, 137 insertions(+), 60 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index b75f9dcf4dbf..9a2b4d561e9e 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -291,6 +291,17 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
 	return 0;
 }
 
+static void io__drain_line(struct io *io, int ch)
+{
+	if (ch == '\n')
+		return;
+	if (ch == -2 && io->data > io->buf && io->data[-1] == '\n')
+		return;
+
+	while (ch >= 0 && ch != '\n')
+		ch = io__get_char(io);
+}
+
 static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 				u32 *prot, u32 *flags, __u64 *offset,
 				u32 *maj, u32 *min,
@@ -299,69 +310,127 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 {
 	__u64 temp;
 	int ch;
-	char *start_pathname = pathname;
+	size_t written = 0;
+	bool overflowed = false;
 
-	if (io__get_hex(io, start) != '-')
+	ch = io__get_hex(io, start);
+	if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
-	if (io__get_hex(io, end) != ' ')
+	}
+	ch = io__get_hex(io, end);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
 	/* map protection and flags bits */
 	*prot = 0;
 	ch = io__get_char(io);
 	if (ch == 'r')
 		*prot |= PROT_READ;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'w')
 		*prot |= PROT_WRITE;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'x')
 		*prot |= PROT_EXEC;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 's')
 		*flags = MAP_SHARED;
 	else if (ch == 'p')
 		*flags = MAP_PRIVATE;
-	else
+	else {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
-	if (io__get_char(io) != ' ')
+	}
+	ch = io__get_char(io);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
-	if (io__get_hex(io, offset) != ' ')
+	ch = io__get_hex(io, offset);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
-	if (io__get_hex(io, &temp) != ':')
+	ch = io__get_hex(io, &temp);
+	if (ch != ':') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	*maj = temp;
-	if (io__get_hex(io, &temp) != ' ')
+	ch = io__get_hex(io, &temp);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	*min = temp;
 
 	ch = io__get_dec(io, inode);
 	if (ch != ' ') {
-		*pathname = '\0';
-		return ch == '\n';
+		if (ch == '\n') {
+			pathname[0] = '\0';
+			return true;
+		}
+		if (!io->eof)
+			io__drain_line(io, ch);
+		return false;
 	}
+
 	do {
 		ch = io__get_char(io);
 	} while (ch == ' ');
+
 	while (true) {
-		if (ch < 0)
-			return false;
-		if (ch == '\0' || ch == '\n' ||
-		    (pathname + 1 - start_pathname) >= pathname_size) {
-			*pathname = '\0';
-			return true;
+		if (ch < 0) {
+			if (overflowed) {
+				strlcpy(pathname, "//toolong", pathname_size);
+				return true;
+			}
+			pathname[written] = '\0';
+			return written > 0;
 		}
-		*pathname++ = ch;
+		if (ch == '\0' || ch == '\n')
+			break;
+
+		if (written < (size_t)pathname_size - 1)
+			pathname[written++] = (char)ch;
+		else
+			overflowed = true;
 		ch = io__get_char(io);
 	}
+
+	if (overflowed)
+		strlcpy(pathname, "//toolong", pathname_size);
+	else
+		pathname[written] = '\0';
+
+	return true;
 }
 
 static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
@@ -463,45 +532,53 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 	while (!io.eof) {
 		static const char anonstr[] = "//anon";
 		size_t size, aligned_size;
-
-		/* ensure null termination since stack will be reused. */
-		event->mmap2.filename[0] = '\0';
+		__u64 start, end, pgoff, ino;
+		u32 prot, flags, maj, min;
 
 		/* 00400000-0040c000 r-xp 00000000 fd:01 41038  /bin/cat */
-		if (!read_proc_maps_line(&io,
-					&event->mmap2.start,
-					&event->mmap2.len,
-					&event->mmap2.prot,
-					&event->mmap2.flags,
-					&event->mmap2.pgoff,
-					&event->mmap2.maj,
-					&event->mmap2.min,
-					&event->mmap2.ino,
-					sizeof(event->mmap2.filename),
-					event->mmap2.filename))
+		/* Read directly into event->mmap2.filename! */
+		if (!read_proc_maps_line(&io, &start, &end,
+					 &prot, &flags, &pgoff,
+					 &maj, &min, &ino,
+					 sizeof(event->mmap2.filename),
+					 event->mmap2.filename)) {
+			if (io.eof)
+				break;
 			continue;
+		}
 
-		if ((rdclock() - t) > timeout) {
-			pr_warning("Reading %s/proc/%d/task/%d/maps time out. "
-				   "You may want to increase "
-				   "the time limit by --proc-map-timeout\n",
-				   machine->root_dir, pid, pid);
-			truncation = true;
-			goto out;
+		if (!strcmp(event->mmap2.filename, ""))
+			strcpy(event->mmap2.filename, anonstr);
+
+		if (hugetlbfs_mnt_len &&
+		    !strncmp(event->mmap2.filename, hugetlbfs_mnt, hugetlbfs_mnt_len)) {
+			strcpy(event->mmap2.filename, anonstr);
+			flags |= MAP_HUGETLB;
 		}
 
-		event->mmap2.ino_generation = 0;
+		size = strlen(event->mmap2.filename) + 1;
+		aligned_size = PERF_ALIGN(size, sizeof(u64));
+
+		event->mmap2.header.type = PERF_RECORD_MMAP2;
 
 		/*
-		 * Just like the kernel, see __perf_event_mmap in kernel/perf_event.c
+		 * Just like the kernel, see perf_misc_flags() in
+		 * kernel/events/core.c
 		 */
 		if (machine__is_host(machine))
 			event->header.misc = PERF_RECORD_MISC_USER;
 		else
 			event->header.misc = PERF_RECORD_MISC_GUEST_USER;
 
-		if ((event->mmap2.prot & PROT_EXEC) == 0) {
-			if (!mmap_data || (event->mmap2.prot & PROT_READ) == 0)
+		if ((rdclock() - t) > timeout) {
+			pr_warning("Reading %s/proc/%d/task/%d/maps time out. You may want to increase the time limit by --proc-map-timeout\n",
+				   machine->root_dir, pid, pid);
+			truncation = true;
+			goto out;
+		}
+
+		if ((prot & PROT_EXEC) == 0) {
+			if (!mmap_data || (prot & PROT_READ) == 0)
 				continue;
 
 			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
@@ -511,26 +588,26 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 		if (truncation)
 			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;
 
-		if (!strcmp(event->mmap2.filename, ""))
-			strcpy(event->mmap2.filename, anonstr);
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
 
-		if (hugetlbfs_mnt_len &&
-		    !strncmp(event->mmap2.filename, hugetlbfs_mnt,
-			     hugetlbfs_mnt_len)) {
-			strcpy(event->mmap2.filename, anonstr);
-			event->mmap2.flags |= MAP_HUGETLB;
-		}
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + machine->id_hdr_size);
 
-		size = strlen(event->mmap2.filename) + 1;
-		aligned_size = PERF_ALIGN(size, sizeof(u64));
-		event->mmap2.len -= event->mmap.start;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - aligned_size));
-		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
-			(aligned_size - size));
 		event->mmap2.header.size += machine->id_hdr_size;
+		event->mmap2.start = start;
+		event->mmap2.len = end - start;
+		event->mmap2.pgoff = pgoff;
+		event->mmap2.maj = maj;
+		event->mmap2.min = min;
+		event->mmap2.ino = ino;
+		event->mmap2.ino_generation = 0;
 		event->mmap2.pid = tgid;
 		event->mmap2.tid = pid;
+		event->mmap2.prot = prot;
+		event->mmap2.flags = flags;
 
 		if (!symbol_conf.no_buildid_mmap2)
 			perf_record_mmap2__read_build_id(&event->mmap2, machine, false);
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v2 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

[Ian Rogers]

Fix potential buffer overruns in perf_event__synthesize_modules_maps_cb()
by safely clamping long DSO names to the mmap/mmap2 filename boundaries.
Explicitly assign and clear the misc flags and union padding across all
iterations to prevent stale Build-ID state from leaking between module
synthesis events.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 70 +++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 9a2b4d561e9e..068323b9510d 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -754,6 +754,7 @@ struct perf_event__synthesize_modules_maps_cb_args {
 	perf_event__handler_t process;
 	struct machine *machine;
 	union perf_event *event;
+	u16 misc;
 };
 
 static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
@@ -761,49 +762,78 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
 	struct perf_event__synthesize_modules_maps_cb_args *args = data;
 	union perf_event *event = args->event;
 	struct dso *dso;
-	size_t size;
+	size_t size, aligned_size;
+	int rc = 0;
 
 	if (!__map__is_kmodule(map))
 		return 0;
 
 	dso = map__dso(map);
 	if (!symbol_conf.no_buildid_mmap2) {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap2.filename))
+			size = sizeof(event->mmap2.filename) - 1;
+
+		strlcpy(event->mmap2.filename, long_name,
+			sizeof(event->mmap2.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap2.header.type = PERF_RECORD_MMAP2;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - size));
-		memset(event->mmap2.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap2.header.misc = args->misc;
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap2.header.size += args->machine->id_hdr_size;
 		event->mmap2.start = map__start(map);
 		event->mmap2.len   = map__size(map);
 		event->mmap2.pid   = args->machine->pid;
 
-		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
-
-		/* Clear stale build ID from previous module iteration */
+		/* Clear stale build ID and entire union from previous module iteration */
 		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
 		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
 		event->mmap2.build_id_size = 0;
+		event->mmap2.__reserved_1 = 0;
+		event->mmap2.__reserved_2 = 0;
 
 		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
 	} else {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap.filename))
+			size = sizeof(event->mmap.filename) - 1;
+
+		strlcpy(event->mmap.filename, long_name,
+			sizeof(event->mmap.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap.header.type = PERF_RECORD_MMAP;
-		event->mmap.header.size = (sizeof(event->mmap) -
-					(sizeof(event->mmap.filename) - size));
-		memset(event->mmap.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap.header.misc = args->misc;
+		event->mmap.header.size =
+			offsetof(struct perf_record_mmap, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap.header.size += args->machine->id_hdr_size;
 		event->mmap.start = map__start(map);
 		event->mmap.len   = map__size(map);
 		event->mmap.pid   = args->machine->pid;
-
-		memcpy(event->mmap.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
 	}
 
 	if (perf_tool__process_synth_event(args->tool, event, args->machine, args->process) != 0)
-		return -1;
+		rc = -1;
 
-	return 0;
+	return rc;
 }
 
 int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__handler_t process,
@@ -828,13 +858,13 @@ int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__han
 	}
 
 	/*
-	 * kernel uses 0 for user space maps, see kernel/perf_event.c
-	 * __perf_event_mmap
+	 * Just like the kernel, see perf_misc_flags() in
+	 * kernel/events/core.c
 	 */
 	if (machine__is_host(machine))
-		args.event->header.misc = PERF_RECORD_MISC_KERNEL;
+		args.misc = PERF_RECORD_MISC_KERNEL;
 	else
-		args.event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
+		args.misc = PERF_RECORD_MISC_GUEST_KERNEL;
 
 	rc = maps__for_each_map(maps, perf_event__synthesize_modules_maps_cb, &args);
 
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v2 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

[Ian Rogers]

Fix a critical logic bug in perf_event__synthesize_mmap2_build_id() where
the wrong union member structure size and offset boundaries were utilized.
Safely calculate the exact maximum allowed filename length to guarantee
absolute stack and alignment boundaries for ID sample trailers, preventing
-E2BIG overruns on very long filenames while meeting strict standard C
compliance.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 068323b9510d..fb4f736f64c0 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -2447,13 +2447,18 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 	size_t filename_len = strlen(filename);
 	size_t ev_len;
 	u64 sample_type = sample->evsel ? sample->evsel->core.attr.sample_type : 0;
-	void *array;
+	void *array = &ev;
 	int ret;
+	size_t max_filename_len;
 
-	if (filename_len >= sizeof(ev.mmap2.filename))
-		return -EINVAL;
+	max_filename_len = sizeof(ev) -
+			   (MAX_ID_HDR_ENTRIES * sizeof(__u64)) -
+			   offsetof(struct perf_record_mmap2, filename) - 1;
 
-	ev_len = sizeof(ev.mmap2) - sizeof(ev.mmap2.filename) + filename_len + 1;
+	if (filename_len > max_filename_len)
+		filename_len = max_filename_len;
+
+	ev_len = offsetof(struct perf_record_mmap2, filename) + filename_len + 1;
 	ev_len = PERF_ALIGN(ev_len, sizeof(u64));
 
 	if (ev_len + MAX_ID_HDR_ENTRIES * sizeof(__u64) > sizeof(ev))
@@ -2473,16 +2478,15 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 
 	ev.mmap2.build_id_size = bid->size;
 	if (ev.mmap2.build_id_size > sizeof(ev.mmap2.build_id))
-		ev.build_id.size = sizeof(ev.mmap2.build_id);
+		ev.mmap2.build_id_size = sizeof(ev.mmap2.build_id);
 	memcpy(ev.mmap2.build_id, bid->data, ev.mmap2.build_id_size);
 
 	ev.mmap2.prot = prot;
 	ev.mmap2.flags = flags;
 
-	memcpy(ev.mmap2.filename, filename, min(strlen(filename), sizeof(ev.mmap.filename)));
+	strlcpy(ev.mmap2.filename, filename, filename_len + 1);
 
-	array = &ev;
-	array += ev.header.size;
+	array = (void *)((char *)&ev + ev.header.size);
 	ret = perf_event__synthesize_id_sample(array, sample_type, sample);
 	if (ret < 0)
 		return ret;
-- 
2.55.0.229.g6434b31f56-goog

Re: [PATCH v2 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] `io__drain_line()` fails to drain the remainder of the line when `ch == -2` is passed, causing parsing synchronization failure.
--

--- Patch [2]: [PATCH v2 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader ---
commit f1400c3fd8b406d3bc0aa09991216359f2f3eb18
Author: Ian Rogers <irogers@google.com>
Subject: perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

This commit addresses logic and boundary issues in the proc maps reader. It
adds explicit line drainage to handle mid-line parsing failures and introduces
timeout handling for truncated map entries.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 5307d707711d8..059dd558a564c 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
[ ... ]
> @@ -291,6 +291,17 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
[ ... ]
> +static void io__drain_line(struct io *io, int ch)
> +{
> +	if (ch == '\n')
> +		return;
> +	if (ch == -2 && io->data > io->buf && io->data[-1] == '\n')
> +		return;
> +
> +	while (ch >= 0 && ch != '\n')
> +		ch = io__get_char(io);

[Severity: Medium]
Will this loop properly drain the line if ch is initially passed as -2?

When read_proc_maps_line() encounters a malformed line where io__get_hex()
or io__get_dec() fails immediately, they return the error code -2. This
value is passed into io__drain_line() as the ch argument.

Because the loop condition requires ch >= 0, passing -2 causes the loop to
be skipped entirely without reading any characters from io__get_char(io).
This appears to leave the stream positioned mid-line, potentially causing
the parser to repeatedly fail character-by-character on the exact same
line, defeating the line synchronization mechanism.

> +}
> +
>  static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260720225200.3810501-1-irogers@google.com?part=2

[PATCH v3 0/4] perf: Fix and optimize maps parsing, boundaries, and bounds safety

[Ian Rogers]

It turns out that PATH_MAX is respected by system calls but isn't
respected by file paths in /proc/pid/maps and /proc/pid/smaps. In the
kernel "//toolong" is placed in the filename of mmap/mmap2 events
where the filename is longer than PATH_MAX, do the same in the
mmap/mmap2 synthesis code to avoid overrunning the event buffer. With
Gemini's help try to address other correctness and overrun issues.

V3 addresses Sashiko AI review feedback:
- Updates io__drain_line() loop condition from a while loop to a
  do-while loop to ensure that when ch == -2 (initial character
  non-hex/dec failure), the loop correctly reads and discards
  characters from io__get_char(io) until a newline or EOF is reached,
  preserving map line synchronization.

V2 addresses community review feedback:
- Corrects read_proc_maps_line() and io__drain_line() to safely handle
  already consumed newlines, preventing valid map data from being skipped.
- Restores the early exit block for timeouts so the TIMEOUT flag is
  always emitted to tools.
- Removes an unused assignment to avoid promoting warnings to build errors.
- Clarifies and dynamically computes the maximum filename length boundaries
  using offsetof() to prevent E2BIG errors regardless of struct layout.

Ian Rogers (4):
  perf find-map: Remove PATH_MAX 128-byte stack array restriction
  perf synthetic-events: Fix line synchronization, bounds, and
    truncation bugs in proc maps reader
  perf synthetic-events: Fix bounds, stale state, and misc flags in
    kernel module synthesis
  perf synthetic-events: Fix bounds and union member access in mmap2
    build_id synthesis

 tools/perf/util/find-map.c         |  10 +-
 tools/perf/util/synthetic-events.c | 288 ++++++++++++++++++++---------
 2 files changed, 208 insertions(+), 90 deletions(-)

-- 
2.55.0.229.g6434b31f56-goog

[PATCH v3 1/4] perf find-map: Remove PATH_MAX 128-byte stack array restriction

[Ian Rogers]

Use getline() to dynamically allocate the required line buffer for maps
parsing, guaranteeing bounds safety and avoiding compiler warnings
by evaluating the return value in the loop condition directly.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/find-map.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
index 7b2300588ece..bba511795a69 100644
--- a/tools/perf/util/find-map.c
+++ b/tools/perf/util/find-map.c
@@ -1,8 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
 static int find_map(void **start, void **end, const char *name)
 {
 	FILE *maps;
-	char line[128];
+	char *line = NULL;
+	size_t len = 0;
 	int found = 0;
 
 	maps = fopen("/proc/self/maps", "r");
@@ -11,7 +16,7 @@ static int find_map(void **start, void **end, const char *name)
 		return -1;
 	}
 
-	while (!found && fgets(line, sizeof(line), maps)) {
+	while (!found && getline(&line, &len, maps) != -1) {
 		int m = -1;
 
 		/* We care only about private r-x mappings. */
@@ -25,6 +30,7 @@ static int find_map(void **start, void **end, const char *name)
 			found = 1;
 	}
 
+	free(line);
 	fclose(maps);
 	return !found;
 }
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v3 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[Ian Rogers]

Fix critical logic and boundary bugs in read_proc_maps_line() and caller.
Ensure any mid-line hex/dec/char parsing failure invokes io__drain_line()
safely, ignoring already-consumed newlines to preserve synchronization
for subsequent map entries. Use standard '//toolong' fallback literal
for over-length pathnames, and emit timeout flags for truncated entries
securely via goto out;.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 197 ++++++++++++++++++++---------
 1 file changed, 137 insertions(+), 60 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index b75f9dcf4dbf..9a2b4d561e9e 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -291,6 +291,17 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
 	return 0;
 }
 
+static void io__drain_line(struct io *io, int ch)
+{
+	if (ch == '\n')
+		return;
+	if (ch == -2 && io->data > io->buf && io->data[-1] == '\n')
+		return;
+
+	while (ch >= 0 && ch != '\n')
+		ch = io__get_char(io);
+}
+
 static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 				u32 *prot, u32 *flags, __u64 *offset,
 				u32 *maj, u32 *min,
@@ -299,69 +310,127 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 {
 	__u64 temp;
 	int ch;
-	char *start_pathname = pathname;
+	size_t written = 0;
+	bool overflowed = false;
 
-	if (io__get_hex(io, start) != '-')
+	ch = io__get_hex(io, start);
+	if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
-	if (io__get_hex(io, end) != ' ')
+	}
+	ch = io__get_hex(io, end);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
 	/* map protection and flags bits */
 	*prot = 0;
 	ch = io__get_char(io);
 	if (ch == 'r')
 		*prot |= PROT_READ;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'w')
 		*prot |= PROT_WRITE;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'x')
 		*prot |= PROT_EXEC;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 's')
 		*flags = MAP_SHARED;
 	else if (ch == 'p')
 		*flags = MAP_PRIVATE;
-	else
+	else {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
-	if (io__get_char(io) != ' ')
+	}
+	ch = io__get_char(io);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
-	if (io__get_hex(io, offset) != ' ')
+	ch = io__get_hex(io, offset);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
-	if (io__get_hex(io, &temp) != ':')
+	ch = io__get_hex(io, &temp);
+	if (ch != ':') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	*maj = temp;
-	if (io__get_hex(io, &temp) != ' ')
+	ch = io__get_hex(io, &temp);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	*min = temp;
 
 	ch = io__get_dec(io, inode);
 	if (ch != ' ') {
-		*pathname = '\0';
-		return ch == '\n';
+		if (ch == '\n') {
+			pathname[0] = '\0';
+			return true;
+		}
+		if (!io->eof)
+			io__drain_line(io, ch);
+		return false;
 	}
+
 	do {
 		ch = io__get_char(io);
 	} while (ch == ' ');
+
 	while (true) {
-		if (ch < 0)
-			return false;
-		if (ch == '\0' || ch == '\n' ||
-		    (pathname + 1 - start_pathname) >= pathname_size) {
-			*pathname = '\0';
-			return true;
+		if (ch < 0) {
+			if (overflowed) {
+				strlcpy(pathname, "//toolong", pathname_size);
+				return true;
+			}
+			pathname[written] = '\0';
+			return written > 0;
 		}
-		*pathname++ = ch;
+		if (ch == '\0' || ch == '\n')
+			break;
+
+		if (written < (size_t)pathname_size - 1)
+			pathname[written++] = (char)ch;
+		else
+			overflowed = true;
 		ch = io__get_char(io);
 	}
+
+	if (overflowed)
+		strlcpy(pathname, "//toolong", pathname_size);
+	else
+		pathname[written] = '\0';
+
+	return true;
 }
 
 static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
@@ -463,45 +532,53 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 	while (!io.eof) {
 		static const char anonstr[] = "//anon";
 		size_t size, aligned_size;
-
-		/* ensure null termination since stack will be reused. */
-		event->mmap2.filename[0] = '\0';
+		__u64 start, end, pgoff, ino;
+		u32 prot, flags, maj, min;
 
 		/* 00400000-0040c000 r-xp 00000000 fd:01 41038  /bin/cat */
-		if (!read_proc_maps_line(&io,
-					&event->mmap2.start,
-					&event->mmap2.len,
-					&event->mmap2.prot,
-					&event->mmap2.flags,
-					&event->mmap2.pgoff,
-					&event->mmap2.maj,
-					&event->mmap2.min,
-					&event->mmap2.ino,
-					sizeof(event->mmap2.filename),
-					event->mmap2.filename))
+		/* Read directly into event->mmap2.filename! */
+		if (!read_proc_maps_line(&io, &start, &end,
+					 &prot, &flags, &pgoff,
+					 &maj, &min, &ino,
+					 sizeof(event->mmap2.filename),
+					 event->mmap2.filename)) {
+			if (io.eof)
+				break;
 			continue;
+		}
 
-		if ((rdclock() - t) > timeout) {
-			pr_warning("Reading %s/proc/%d/task/%d/maps time out. "
-				   "You may want to increase "
-				   "the time limit by --proc-map-timeout\n",
-				   machine->root_dir, pid, pid);
-			truncation = true;
-			goto out;
+		if (!strcmp(event->mmap2.filename, ""))
+			strcpy(event->mmap2.filename, anonstr);
+
+		if (hugetlbfs_mnt_len &&
+		    !strncmp(event->mmap2.filename, hugetlbfs_mnt, hugetlbfs_mnt_len)) {
+			strcpy(event->mmap2.filename, anonstr);
+			flags |= MAP_HUGETLB;
 		}
 
-		event->mmap2.ino_generation = 0;
+		size = strlen(event->mmap2.filename) + 1;
+		aligned_size = PERF_ALIGN(size, sizeof(u64));
+
+		event->mmap2.header.type = PERF_RECORD_MMAP2;
 
 		/*
-		 * Just like the kernel, see __perf_event_mmap in kernel/perf_event.c
+		 * Just like the kernel, see perf_misc_flags() in
+		 * kernel/events/core.c
 		 */
 		if (machine__is_host(machine))
 			event->header.misc = PERF_RECORD_MISC_USER;
 		else
 			event->header.misc = PERF_RECORD_MISC_GUEST_USER;
 
-		if ((event->mmap2.prot & PROT_EXEC) == 0) {
-			if (!mmap_data || (event->mmap2.prot & PROT_READ) == 0)
+		if ((rdclock() - t) > timeout) {
+			pr_warning("Reading %s/proc/%d/task/%d/maps time out. You may want to increase the time limit by --proc-map-timeout\n",
+				   machine->root_dir, pid, pid);
+			truncation = true;
+			goto out;
+		}
+
+		if ((prot & PROT_EXEC) == 0) {
+			if (!mmap_data || (prot & PROT_READ) == 0)
 				continue;
 
 			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
@@ -511,26 +588,26 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 		if (truncation)
 			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;
 
-		if (!strcmp(event->mmap2.filename, ""))
-			strcpy(event->mmap2.filename, anonstr);
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
 
-		if (hugetlbfs_mnt_len &&
-		    !strncmp(event->mmap2.filename, hugetlbfs_mnt,
-			     hugetlbfs_mnt_len)) {
-			strcpy(event->mmap2.filename, anonstr);
-			event->mmap2.flags |= MAP_HUGETLB;
-		}
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + machine->id_hdr_size);
 
-		size = strlen(event->mmap2.filename) + 1;
-		aligned_size = PERF_ALIGN(size, sizeof(u64));
-		event->mmap2.len -= event->mmap.start;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - aligned_size));
-		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
-			(aligned_size - size));
 		event->mmap2.header.size += machine->id_hdr_size;
+		event->mmap2.start = start;
+		event->mmap2.len = end - start;
+		event->mmap2.pgoff = pgoff;
+		event->mmap2.maj = maj;
+		event->mmap2.min = min;
+		event->mmap2.ino = ino;
+		event->mmap2.ino_generation = 0;
 		event->mmap2.pid = tgid;
 		event->mmap2.tid = pid;
+		event->mmap2.prot = prot;
+		event->mmap2.flags = flags;
 
 		if (!symbol_conf.no_buildid_mmap2)
 			perf_record_mmap2__read_build_id(&event->mmap2, machine, false);
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v3 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

[Ian Rogers]

Fix potential buffer overruns in perf_event__synthesize_modules_maps_cb()
by safely clamping long DSO names to the mmap/mmap2 filename boundaries.
Explicitly assign and clear the misc flags and union padding across all
iterations to prevent stale Build-ID state from leaking between module
synthesis events.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 70 +++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 20 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 9a2b4d561e9e..068323b9510d 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -754,6 +754,7 @@ struct perf_event__synthesize_modules_maps_cb_args {
 	perf_event__handler_t process;
 	struct machine *machine;
 	union perf_event *event;
+	u16 misc;
 };
 
 static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
@@ -761,49 +762,78 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
 	struct perf_event__synthesize_modules_maps_cb_args *args = data;
 	union perf_event *event = args->event;
 	struct dso *dso;
-	size_t size;
+	size_t size, aligned_size;
+	int rc = 0;
 
 	if (!__map__is_kmodule(map))
 		return 0;
 
 	dso = map__dso(map);
 	if (!symbol_conf.no_buildid_mmap2) {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap2.filename))
+			size = sizeof(event->mmap2.filename) - 1;
+
+		strlcpy(event->mmap2.filename, long_name,
+			sizeof(event->mmap2.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap2.header.type = PERF_RECORD_MMAP2;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - size));
-		memset(event->mmap2.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap2.header.misc = args->misc;
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap2.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap2.header.size += args->machine->id_hdr_size;
 		event->mmap2.start = map__start(map);
 		event->mmap2.len   = map__size(map);
 		event->mmap2.pid   = args->machine->pid;
 
-		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
-
-		/* Clear stale build ID from previous module iteration */
+		/* Clear stale build ID and entire union from previous module iteration */
 		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
 		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
 		event->mmap2.build_id_size = 0;
+		event->mmap2.__reserved_1 = 0;
+		event->mmap2.__reserved_2 = 0;
 
 		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
 	} else {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap.filename))
+			size = sizeof(event->mmap.filename) - 1;
+
+		strlcpy(event->mmap.filename, long_name,
+			sizeof(event->mmap.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap.header.type = PERF_RECORD_MMAP;
-		event->mmap.header.size = (sizeof(event->mmap) -
-					(sizeof(event->mmap.filename) - size));
-		memset(event->mmap.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap.header.misc = args->misc;
+		event->mmap.header.size =
+			offsetof(struct perf_record_mmap, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset(event->mmap.filename + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap.header.size += args->machine->id_hdr_size;
 		event->mmap.start = map__start(map);
 		event->mmap.len   = map__size(map);
 		event->mmap.pid   = args->machine->pid;
-
-		memcpy(event->mmap.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
 	}
 
 	if (perf_tool__process_synth_event(args->tool, event, args->machine, args->process) != 0)
-		return -1;
+		rc = -1;
 
-	return 0;
+	return rc;
 }
 
 int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__handler_t process,
@@ -828,13 +858,13 @@ int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__han
 	}
 
 	/*
-	 * kernel uses 0 for user space maps, see kernel/perf_event.c
-	 * __perf_event_mmap
+	 * Just like the kernel, see perf_misc_flags() in
+	 * kernel/events/core.c
 	 */
 	if (machine__is_host(machine))
-		args.event->header.misc = PERF_RECORD_MISC_KERNEL;
+		args.misc = PERF_RECORD_MISC_KERNEL;
 	else
-		args.event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
+		args.misc = PERF_RECORD_MISC_GUEST_KERNEL;
 
 	rc = maps__for_each_map(maps, perf_event__synthesize_modules_maps_cb, &args);
 
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v3 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

[Ian Rogers]

Fix a critical logic bug in perf_event__synthesize_mmap2_build_id() where
the wrong union member structure size and offset boundaries were utilized.
Safely calculate the exact maximum allowed filename length to guarantee
absolute stack and alignment boundaries for ID sample trailers, preventing
-E2BIG overruns on very long filenames while meeting strict standard C
compliance.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 068323b9510d..6477a726c8ba 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -298,8 +298,9 @@ static void io__drain_line(struct io *io, int ch)
 	if (ch == -2 && io->data > io->buf && io->data[-1] == '\n')
 		return;
 
-	while (ch >= 0 && ch != '\n')
+	do {
 		ch = io__get_char(io);
+	} while (ch >= 0 && ch != '\n');
 }
 
 static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
@@ -2447,13 +2448,18 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 	size_t filename_len = strlen(filename);
 	size_t ev_len;
 	u64 sample_type = sample->evsel ? sample->evsel->core.attr.sample_type : 0;
-	void *array;
+	void *array = &ev;
 	int ret;
+	size_t max_filename_len;
 
-	if (filename_len >= sizeof(ev.mmap2.filename))
-		return -EINVAL;
+	max_filename_len = sizeof(ev) -
+			   (MAX_ID_HDR_ENTRIES * sizeof(__u64)) -
+			   offsetof(struct perf_record_mmap2, filename) - 1;
 
-	ev_len = sizeof(ev.mmap2) - sizeof(ev.mmap2.filename) + filename_len + 1;
+	if (filename_len > max_filename_len)
+		filename_len = max_filename_len;
+
+	ev_len = offsetof(struct perf_record_mmap2, filename) + filename_len + 1;
 	ev_len = PERF_ALIGN(ev_len, sizeof(u64));
 
 	if (ev_len + MAX_ID_HDR_ENTRIES * sizeof(__u64) > sizeof(ev))
@@ -2473,16 +2479,15 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 
 	ev.mmap2.build_id_size = bid->size;
 	if (ev.mmap2.build_id_size > sizeof(ev.mmap2.build_id))
-		ev.build_id.size = sizeof(ev.mmap2.build_id);
+		ev.mmap2.build_id_size = sizeof(ev.mmap2.build_id);
 	memcpy(ev.mmap2.build_id, bid->data, ev.mmap2.build_id_size);
 
 	ev.mmap2.prot = prot;
 	ev.mmap2.flags = flags;
 
-	memcpy(ev.mmap2.filename, filename, min(strlen(filename), sizeof(ev.mmap.filename)));
+	strlcpy(ev.mmap2.filename, filename, filename_len + 1);
 
-	array = &ev;
-	array += ev.header.size;
+	array = (void *)((char *)&ev + ev.header.size);
 	ret = perf_event__synthesize_id_sample(array, sample_type, sample);
 	if (ret < 0)
 		return ret;
-- 
2.55.0.229.g6434b31f56-goog

Re: [PATCH v3 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] The memset used to clear the filename padding and ID header trailer will trigger a _FORTIFY_SOURCE runtime abort when a DSO name length approaches PATH_MAX.
--

--- Patch [3]: [PATCH v3 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis ---
commit e862d233381463bc8c1e84b7d335152fe0a7c118
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

This commit clamps long DSO names to mmap/mmap2 filename boundaries to prevent
buffer overruns in perf_event__synthesize_modules_maps_cb(). It also explicitly
clears misc flags and union padding to prevent stale Build-ID state from leaking
between module synthesis events.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c

[ ... ]

> @@ -761,49 +762,78 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
>  	if (!symbol_conf.no_buildid_mmap2) {
>  		const char *long_name = dso__long_name(dso);
>  
> -		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
> +		size = strlen(long_name);
> +		if (size >= sizeof(event->mmap2.filename))
> +			size = sizeof(event->mmap2.filename) - 1;
> +
> +		strlcpy(event->mmap2.filename, long_name,
> +			sizeof(event->mmap2.filename));
> +
> +		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
>  		event->mmap2.header.type = PERF_RECORD_MMAP2;
> -		event->mmap2.header.size = (sizeof(event->mmap2) -
> -					(sizeof(event->mmap2.filename) - size));
> -		memset(event->mmap2.filename + size, 0, args->machine->id_hdr_size);
> +		event->mmap2.header.misc = args->misc;
> +		event->mmap2.header.size =
> +			offsetof(struct perf_record_mmap2, filename) +
> +			aligned_size;
> +
> +		/* Zero the padding and ID header trailer safely! */
> +		memset(event->mmap2.filename + size, 0,
> +		       (aligned_size - size) + args->machine->id_hdr_size);

[Severity: High]
This is a pre-existing issue, but can this memset trigger a _FORTIFY_SOURCE
runtime abort when a DSO name length approaches PATH_MAX?

The event->mmap2.filename field is declared as a fixed-size array of
PATH_MAX (4096 bytes). If a kernel module path is very long, size is clamped
to 4095 and aligned_size evaluates to 4096. The memset then attempts to write
(1 + args->machine->id_hdr_size) bytes starting at event->mmap2.filename + 4095.

Because the memset is anchored to the filename member array, _FORTIFY_SOURCE
dynamically tracks that there is only 1 byte remaining in that specific member.
Since 1 + id_hdr_size > 1, this exceeds the compiler-enforced array bound,
triggering __chk_fail() and terminating perf, even though the underlying
allocation is large enough.

> +
>  		event->mmap2.header.size += args->machine->id_hdr_size;
>  		event->mmap2.start = map__start(map);

[ ... ]

>  		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
>  	} else {
> -		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
> +		const char *long_name = dso__long_name(dso);
> +
> +		size = strlen(long_name);
> +		if (size >= sizeof(event->mmap.filename))
> +			size = sizeof(event->mmap.filename) - 1;
> +
> +		strlcpy(event->mmap.filename, long_name,
> +			sizeof(event->mmap.filename));
> +
> +		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
>  		event->mmap.header.type = PERF_RECORD_MMAP;
> -		event->mmap.header.size = (sizeof(event->mmap) -
> -					(sizeof(event->mmap.filename) - size));
> -		memset(event->mmap.filename + size, 0, args->machine->id_hdr_size);
> +		event->mmap.header.misc = args->misc;
> +		event->mmap.header.size =
> +			offsetof(struct perf_record_mmap, filename) +
> +			aligned_size;
> +
> +		/* Zero the padding and ID header trailer safely! */
> +		memset(event->mmap.filename + size, 0,
> +		       (aligned_size - size) + args->machine->id_hdr_size);

[Severity: High]
This is a pre-existing issue, but this memset is subject to the same
_FORTIFY_SOURCE abort as the mmap2 case above when the DSO name approaches
PATH_MAX and sample IDs are enabled.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721173347.9163-1-irogers@google.com?part=3

Re: [PATCH v3 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] io__drain_line() fails to drain the line when a parsing error occurs, breaking map parsing synchronization and causing inefficient cascading failures.
--

--- Patch [2]: [PATCH v3 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader ---
commit ffbc393b4ac8d55ab5ee2db18d5f9a92e83c09d1
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

This commit fixes logic and boundary bugs in read_proc_maps_line() and its
callers. It adds io__drain_line() to safely ignore already-consumed
newlines and preserve synchronization for subsequent map entries.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 5307d707711d8..059dd558a564c 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -291,6 +291,17 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
>  	return 0;
>  }
>  
> +static void io__drain_line(struct io *io, int ch)
> +{
> +	if (ch == '\n')
> +		return;
> +	if (ch == -2 && io->data > io->buf && io->data[-1] == '\n')
> +		return;
> +
> +	while (ch >= 0 && ch != '\n')
> +		ch = io__get_char(io);

[Severity: Medium]
Will this loop correctly drain the line when a parsing error occurs?

When io__get_hex() or io__get_dec() encounters an invalid first character,
they consume it and return -2. read_proc_maps_line() then calls
io__drain_line(io, -2).

Because the loop condition strictly requires ch >= 0, it will skip entirely
when passed the -2 error code, returning without consuming any characters.

Instead of draining the rest of the line, the parser will re-evaluate every
remaining character as the potential start of a new map entry, leading to
parsing desynchronization and a tight loop of failures that could trigger
the timeout watchdog.

> +}
> +
>  static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
>  				u32 *prot, u32 *flags, __u64 *offset,
>  				u32 *maj, u32 *min,
> @@ -299,69 +310,127 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
>  {
>  	__u64 temp;
>  	int ch;
> -	char *start_pathname = pathname;
> +	size_t written = 0;
> +	bool overflowed = false;
>  
> -	if (io__get_hex(io, start) != '-')
> +	ch = io__get_hex(io, start);
> +	if (ch != '-') {
> +		if (!io->eof)
> +			io__drain_line(io, ch);
>  		return false;
> -	if (io__get_hex(io, end) != ' ')
> +	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721173347.9163-1-irogers@google.com?part=2

[PATCH v4 0/4] perf: Fix and optimize maps parsing, boundaries, and bounds safety

[Ian Rogers]

It turns out that PATH_MAX is respected by system calls but isn't
respected by file paths in /proc/pid/maps and /proc/pid/smaps. In the
kernel "//toolong" is placed in the filename of mmap/mmap2 events
where the filename is longer than PATH_MAX, do the same in the
mmap/mmap2 synthesis code to avoid overrunning the event buffer -
note, the filename buffer is bounds checked but this makes the
synthesis more similar to the kernel approach. With Gemini's help try
to address other correctness and overrun issues.

V4 addresses review feedback:
- Ensures io__drain_line()'s do-while loop is properly included and
  committed directly within Patch 2. When ch == -2 is passed on parsing
  errors, the loop correctly reads and discards remaining line
  characters until a newline or EOF is reached, preventing tight failure
  loops and preserving line synchronization.
- Replaces member array memset destination pointers in Patches 2 & 3
  with offsetof() casts on (char *)event to avoid _FORTIFY_SOURCE
  runtime array bound aborts when zeroing padding trailers for long
  pathnames.

V3 addresses review feedback:
- Updates io__drain_line() loop condition from a while loop to a
  do-while loop to ensure initial non-hex/dec failures correctly
  drain line remnants.

V2 addresses community review feedback:
- Corrects read_proc_maps_line() and io__drain_line() to safely handle
  already consumed newlines, preventing valid map data from being skipped.
- Restores the early exit block for timeouts so the TIMEOUT flag is
  always emitted to tools.
- Removes an unused assignment to avoid promoting warnings to build errors.
- Clarifies and dynamically computes the maximum filename length boundaries
  using offsetof() to prevent E2BIG errors regardless of struct layout.

Ian Rogers (4):
  perf find-map: Remove PATH_MAX 128-byte stack array restriction
  perf synthetic-events: Fix line synchronization, bounds, and
    truncation bugs in proc maps reader
  perf synthetic-events: Fix bounds, stale state, and misc flags in
    kernel module synthesis
  perf synthetic-events: Fix bounds and union member access in mmap2
    build_id synthesis

 tools/perf/util/find-map.c         |  10 +-
 tools/perf/util/synthetic-events.c | 288 ++++++++++++++++++++---------
 2 files changed, 208 insertions(+), 90 deletions(-)

-- 
2.55.0.229.g6434b31f56-goog

[PATCH v4 1/4] perf find-map: Remove PATH_MAX 128-byte stack array restriction

[Ian Rogers]

Use getline() to dynamically allocate the required line buffer for maps
parsing, guaranteeing bounds safety and avoiding compiler warnings
by evaluating the return value in the loop condition directly.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/find-map.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/find-map.c b/tools/perf/util/find-map.c
index 7b2300588ece..bba511795a69 100644
--- a/tools/perf/util/find-map.c
+++ b/tools/perf/util/find-map.c
@@ -1,8 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
 static int find_map(void **start, void **end, const char *name)
 {
 	FILE *maps;
-	char line[128];
+	char *line = NULL;
+	size_t len = 0;
 	int found = 0;
 
 	maps = fopen("/proc/self/maps", "r");
@@ -11,7 +16,7 @@ static int find_map(void **start, void **end, const char *name)
 		return -1;
 	}
 
-	while (!found && fgets(line, sizeof(line), maps)) {
+	while (!found && getline(&line, &len, maps) != -1) {
 		int m = -1;
 
 		/* We care only about private r-x mappings. */
@@ -25,6 +30,7 @@ static int find_map(void **start, void **end, const char *name)
 			found = 1;
 	}
 
+	free(line);
 	fclose(maps);
 	return !found;
 }
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v4 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[Ian Rogers]

Fix critical logic and boundary bugs in read_proc_maps_line() and caller.
Ensure any mid-line hex/dec/char parsing failure invokes io__drain_line()
safely, using a do-while loop to read and discard remaining characters
until a newline or EOF is reached. Use standard '//toolong' fallback
literal for over-length pathnames, emit timeout flags for truncated
entries securely via goto out;, and cast event buffer pointers to avoid
_FORTIFY_SOURCE array bounds aborts when zeroing trailers.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 203 ++++++++++++++++++++---------
 1 file changed, 138 insertions(+), 65 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index b75f9dcf4dbf..60bdf2d918ea 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -291,6 +291,18 @@ static int perf_event__synthesize_fork(const struct perf_tool *tool,
 	return 0;
 }
 
+static void io__drain_line(struct io *io, int ch)
+{
+	if (ch == '\n')
+		return;
+	if (ch == -2 && io->data > io->buf && io->data[-1] == '\n')
+		return;
+
+	do {
+		ch = io__get_char(io);
+	} while (ch >= 0 && ch != '\n');
+}
+
 static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 				u32 *prot, u32 *flags, __u64 *offset,
 				u32 *maj, u32 *min,
@@ -299,69 +311,127 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
 {
 	__u64 temp;
 	int ch;
-	char *start_pathname = pathname;
+	size_t written = 0;
+	bool overflowed = false;
 
-	if (io__get_hex(io, start) != '-')
+	ch = io__get_hex(io, start);
+	if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
-	if (io__get_hex(io, end) != ' ')
+	}
+	ch = io__get_hex(io, end);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
 	/* map protection and flags bits */
 	*prot = 0;
 	ch = io__get_char(io);
 	if (ch == 'r')
 		*prot |= PROT_READ;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'w')
 		*prot |= PROT_WRITE;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 'x')
 		*prot |= PROT_EXEC;
-	else if (ch != '-')
+	else if (ch != '-') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	ch = io__get_char(io);
 	if (ch == 's')
 		*flags = MAP_SHARED;
 	else if (ch == 'p')
 		*flags = MAP_PRIVATE;
-	else
+	else {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
-	if (io__get_char(io) != ' ')
+	}
+	ch = io__get_char(io);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
-	if (io__get_hex(io, offset) != ' ')
+	ch = io__get_hex(io, offset);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 
-	if (io__get_hex(io, &temp) != ':')
+	ch = io__get_hex(io, &temp);
+	if (ch != ':') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	*maj = temp;
-	if (io__get_hex(io, &temp) != ' ')
+	ch = io__get_hex(io, &temp);
+	if (ch != ' ') {
+		if (!io->eof)
+			io__drain_line(io, ch);
 		return false;
+	}
 	*min = temp;
 
 	ch = io__get_dec(io, inode);
 	if (ch != ' ') {
-		*pathname = '\0';
-		return ch == '\n';
+		if (ch == '\n') {
+			pathname[0] = '\0';
+			return true;
+		}
+		if (!io->eof)
+			io__drain_line(io, ch);
+		return false;
 	}
+
 	do {
 		ch = io__get_char(io);
 	} while (ch == ' ');
+
 	while (true) {
-		if (ch < 0)
-			return false;
-		if (ch == '\0' || ch == '\n' ||
-		    (pathname + 1 - start_pathname) >= pathname_size) {
-			*pathname = '\0';
-			return true;
+		if (ch < 0) {
+			if (overflowed) {
+				strlcpy(pathname, "//toolong", pathname_size);
+				return true;
+			}
+			pathname[written] = '\0';
+			return written > 0;
 		}
-		*pathname++ = ch;
+		if (ch == '\0' || ch == '\n')
+			break;
+
+		if (written < (size_t)pathname_size - 1)
+			pathname[written++] = (char)ch;
+		else
+			overflowed = true;
 		ch = io__get_char(io);
 	}
+
+	if (overflowed)
+		strlcpy(pathname, "//toolong", pathname_size);
+	else
+		pathname[written] = '\0';
+
+	return true;
 }
 
 static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
@@ -463,45 +533,53 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 	while (!io.eof) {
 		static const char anonstr[] = "//anon";
 		size_t size, aligned_size;
-
-		/* ensure null termination since stack will be reused. */
-		event->mmap2.filename[0] = '\0';
+		__u64 start, end, pgoff, ino;
+		u32 prot, flags, maj, min;
 
 		/* 00400000-0040c000 r-xp 00000000 fd:01 41038  /bin/cat */
-		if (!read_proc_maps_line(&io,
-					&event->mmap2.start,
-					&event->mmap2.len,
-					&event->mmap2.prot,
-					&event->mmap2.flags,
-					&event->mmap2.pgoff,
-					&event->mmap2.maj,
-					&event->mmap2.min,
-					&event->mmap2.ino,
-					sizeof(event->mmap2.filename),
-					event->mmap2.filename))
+		/* Read directly into event->mmap2.filename! */
+		if (!read_proc_maps_line(&io, &start, &end,
+					 &prot, &flags, &pgoff,
+					 &maj, &min, &ino,
+					 sizeof(event->mmap2.filename),
+					 event->mmap2.filename)) {
+			if (io.eof)
+				break;
 			continue;
+		}
 
-		if ((rdclock() - t) > timeout) {
-			pr_warning("Reading %s/proc/%d/task/%d/maps time out. "
-				   "You may want to increase "
-				   "the time limit by --proc-map-timeout\n",
-				   machine->root_dir, pid, pid);
-			truncation = true;
-			goto out;
+		if (!strcmp(event->mmap2.filename, ""))
+			strcpy(event->mmap2.filename, anonstr);
+
+		if (hugetlbfs_mnt_len &&
+		    !strncmp(event->mmap2.filename, hugetlbfs_mnt, hugetlbfs_mnt_len)) {
+			strcpy(event->mmap2.filename, anonstr);
+			flags |= MAP_HUGETLB;
 		}
 
-		event->mmap2.ino_generation = 0;
+		size = strlen(event->mmap2.filename) + 1;
+		aligned_size = PERF_ALIGN(size, sizeof(u64));
+
+		event->mmap2.header.type = PERF_RECORD_MMAP2;
 
 		/*
-		 * Just like the kernel, see __perf_event_mmap in kernel/perf_event.c
+		 * Just like the kernel, see perf_misc_flags() in
+		 * kernel/events/core.c
 		 */
 		if (machine__is_host(machine))
 			event->header.misc = PERF_RECORD_MISC_USER;
 		else
 			event->header.misc = PERF_RECORD_MISC_GUEST_USER;
 
-		if ((event->mmap2.prot & PROT_EXEC) == 0) {
-			if (!mmap_data || (event->mmap2.prot & PROT_READ) == 0)
+		if ((rdclock() - t) > timeout) {
+			pr_warning("Reading %s/proc/%d/task/%d/maps time out. You may want to increase the time limit by --proc-map-timeout\n",
+				   machine->root_dir, pid, pid);
+			truncation = true;
+			goto out;
+		}
+
+		if ((prot & PROT_EXEC) == 0) {
+			if (!mmap_data || (prot & PROT_READ) == 0)
 				continue;
 
 			event->header.misc |= PERF_RECORD_MISC_MMAP_DATA;
@@ -511,26 +589,26 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
 		if (truncation)
 			event->header.misc |= PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT;
 
-		if (!strcmp(event->mmap2.filename, ""))
-			strcpy(event->mmap2.filename, anonstr);
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
 
-		if (hugetlbfs_mnt_len &&
-		    !strncmp(event->mmap2.filename, hugetlbfs_mnt,
-			     hugetlbfs_mnt_len)) {
-			strcpy(event->mmap2.filename, anonstr);
-			event->mmap2.flags |= MAP_HUGETLB;
-		}
+		/* Zero the padding and ID header trailer safely! */
+		memset((char *)event + offsetof(struct perf_record_mmap2, filename) + size, 0,
+		       (aligned_size - size) + machine->id_hdr_size);
 
-		size = strlen(event->mmap2.filename) + 1;
-		aligned_size = PERF_ALIGN(size, sizeof(u64));
-		event->mmap2.len -= event->mmap.start;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - aligned_size));
-		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
-			(aligned_size - size));
 		event->mmap2.header.size += machine->id_hdr_size;
+		event->mmap2.start = start;
+		event->mmap2.len = end - start;
+		event->mmap2.pgoff = pgoff;
+		event->mmap2.maj = maj;
+		event->mmap2.min = min;
+		event->mmap2.ino = ino;
+		event->mmap2.ino_generation = 0;
 		event->mmap2.pid = tgid;
 		event->mmap2.tid = pid;
+		event->mmap2.prot = prot;
+		event->mmap2.flags = flags;
 
 		if (!symbol_conf.no_buildid_mmap2)
 			perf_record_mmap2__read_build_id(&event->mmap2, machine, false);
@@ -703,11 +781,6 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
 
 		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
 
-		/* Clear stale build ID from previous module iteration */
-		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
-		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
-		event->mmap2.build_id_size = 0;
-
 		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
 	} else {
 		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v4 3/4] perf synthetic-events: Fix bounds, stale state, and misc flags in kernel module synthesis

[Ian Rogers]

Clamp long DSO names to mmap/mmap2 filename boundaries to prevent
buffer overruns in perf_event__synthesize_modules_maps_cb(). Explicitly
clear misc flags and union padding to prevent stale Build-ID state from
leaking between module synthesis events, and cast event buffer pointers
to avoid _FORTIFY_SOURCE array bounds aborts when zeroing padding
trailers.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 71 ++++++++++++++++++++++--------
 1 file changed, 53 insertions(+), 18 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index 60bdf2d918ea..e547874b77b2 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -755,6 +755,7 @@ struct perf_event__synthesize_modules_maps_cb_args {
 	perf_event__handler_t process;
 	struct machine *machine;
 	union perf_event *event;
+	u16 misc;
 };
 
 static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
@@ -762,44 +763,78 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
 	struct perf_event__synthesize_modules_maps_cb_args *args = data;
 	union perf_event *event = args->event;
 	struct dso *dso;
-	size_t size;
+	size_t size, aligned_size;
+	int rc = 0;
 
 	if (!__map__is_kmodule(map))
 		return 0;
 
 	dso = map__dso(map);
 	if (!symbol_conf.no_buildid_mmap2) {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap2.filename))
+			size = sizeof(event->mmap2.filename) - 1;
+
+		strlcpy(event->mmap2.filename, long_name,
+			sizeof(event->mmap2.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap2.header.type = PERF_RECORD_MMAP2;
-		event->mmap2.header.size = (sizeof(event->mmap2) -
-					(sizeof(event->mmap2.filename) - size));
-		memset(event->mmap2.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap2.header.misc = args->misc;
+		event->mmap2.header.size =
+			offsetof(struct perf_record_mmap2, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset((char *)event + offsetof(struct perf_record_mmap2, filename) + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap2.header.size += args->machine->id_hdr_size;
 		event->mmap2.start = map__start(map);
 		event->mmap2.len   = map__size(map);
 		event->mmap2.pid   = args->machine->pid;
 
-		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
+		/* Clear stale build ID and entire union from previous module iteration */
+		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
+		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
+		event->mmap2.build_id_size = 0;
+		event->mmap2.__reserved_1 = 0;
+		event->mmap2.__reserved_2 = 0;
 
 		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
 	} else {
-		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));
+		const char *long_name = dso__long_name(dso);
+
+		size = strlen(long_name);
+		if (size >= sizeof(event->mmap.filename))
+			size = sizeof(event->mmap.filename) - 1;
+
+		strlcpy(event->mmap.filename, long_name,
+			sizeof(event->mmap.filename));
+
+		aligned_size = PERF_ALIGN(size + 1, sizeof(u64));
 		event->mmap.header.type = PERF_RECORD_MMAP;
-		event->mmap.header.size = (sizeof(event->mmap) -
-					(sizeof(event->mmap.filename) - size));
-		memset(event->mmap.filename + size, 0, args->machine->id_hdr_size);
+		event->mmap.header.misc = args->misc;
+		event->mmap.header.size =
+			offsetof(struct perf_record_mmap, filename) +
+			aligned_size;
+
+		/* Zero the padding and ID header trailer safely! */
+		memset((char *)event + offsetof(struct perf_record_mmap, filename) + size, 0,
+		       (aligned_size - size) + args->machine->id_hdr_size);
+
 		event->mmap.header.size += args->machine->id_hdr_size;
 		event->mmap.start = map__start(map);
 		event->mmap.len   = map__size(map);
 		event->mmap.pid   = args->machine->pid;
-
-		memcpy(event->mmap.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
 	}
 
 	if (perf_tool__process_synth_event(args->tool, event, args->machine, args->process) != 0)
-		return -1;
+		rc = -1;
 
-	return 0;
+	return rc;
 }
 
 int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__handler_t process,
@@ -824,13 +859,13 @@ int perf_event__synthesize_modules(const struct perf_tool *tool, perf_event__han
 	}
 
 	/*
-	 * kernel uses 0 for user space maps, see kernel/perf_event.c
-	 * __perf_event_mmap
+	 * Just like the kernel, see perf_misc_flags() in
+	 * kernel/events/core.c
 	 */
 	if (machine__is_host(machine))
-		args.event->header.misc = PERF_RECORD_MISC_KERNEL;
+		args.misc = PERF_RECORD_MISC_KERNEL;
 	else
-		args.event->header.misc = PERF_RECORD_MISC_GUEST_KERNEL;
+		args.misc = PERF_RECORD_MISC_GUEST_KERNEL;
 
 	rc = maps__for_each_map(maps, perf_event__synthesize_modules_maps_cb, &args);
 
-- 
2.55.0.229.g6434b31f56-goog

[PATCH v4 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

[Ian Rogers]

Fix a critical logic bug in perf_event__synthesize_mmap2_build_id() where
the wrong union member structure size and offset boundaries were utilized.
Safely calculate the exact maximum allowed filename length to guarantee
absolute stack and alignment boundaries for ID sample trailers, preventing
-E2BIG overruns on very long filenames while meeting strict standard C
compliance.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/util/synthetic-events.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index e547874b77b2..06a960e8ba85 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -2448,13 +2448,18 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 	size_t filename_len = strlen(filename);
 	size_t ev_len;
 	u64 sample_type = sample->evsel ? sample->evsel->core.attr.sample_type : 0;
-	void *array;
+	void *array = &ev;
 	int ret;
+	size_t max_filename_len;
 
-	if (filename_len >= sizeof(ev.mmap2.filename))
-		return -EINVAL;
+	max_filename_len = sizeof(ev) -
+			   (MAX_ID_HDR_ENTRIES * sizeof(__u64)) -
+			   offsetof(struct perf_record_mmap2, filename) - 1;
 
-	ev_len = sizeof(ev.mmap2) - sizeof(ev.mmap2.filename) + filename_len + 1;
+	if (filename_len > max_filename_len)
+		filename_len = max_filename_len;
+
+	ev_len = offsetof(struct perf_record_mmap2, filename) + filename_len + 1;
 	ev_len = PERF_ALIGN(ev_len, sizeof(u64));
 
 	if (ev_len + MAX_ID_HDR_ENTRIES * sizeof(__u64) > sizeof(ev))
@@ -2474,16 +2479,15 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
 
 	ev.mmap2.build_id_size = bid->size;
 	if (ev.mmap2.build_id_size > sizeof(ev.mmap2.build_id))
-		ev.build_id.size = sizeof(ev.mmap2.build_id);
+		ev.mmap2.build_id_size = sizeof(ev.mmap2.build_id);
 	memcpy(ev.mmap2.build_id, bid->data, ev.mmap2.build_id_size);
 
 	ev.mmap2.prot = prot;
 	ev.mmap2.flags = flags;
 
-	memcpy(ev.mmap2.filename, filename, min(strlen(filename), sizeof(ev.mmap.filename)));
+	strlcpy(ev.mmap2.filename, filename, filename_len + 1);
 
-	array = &ev;
-	array += ev.header.size;
+	array = (void *)((char *)&ev + ev.header.size);
 	ret = perf_event__synthesize_id_sample(array, sample_type, sample);
 	if (ret < 0)
 		return ret;
-- 
2.55.0.229.g6434b31f56-goog

Re: [PATCH v4 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Latent buffer overflow and potential FORTIFY_SOURCE abort due to incorrect string length bounds check against union capacity instead of array size.
--

--- Patch [4]: [PATCH v4 4/4] perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis ---
commit a02cc1d93b140eea5444d6b7ee95e98c02c00905
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix bounds and union member access in mmap2 build_id synthesis

This commit modifies bounds and union member access in mmap2 build_id
synthesis. It replaces the previous array-based bounds check with a new
calculation based on the size of the event union.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 63c9c85b02f37..8928c6964fc9d 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
[ ... ]
> @@ -2448,13 +2448,18 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
>  	size_t filename_len = strlen(filename);
>  	size_t ev_len;
>  	u64 sample_type = sample->evsel ? sample->evsel->core.attr.sample_type : 0;
> -	void *array;
> +	void *array = &ev;
>  	int ret;
> +	size_t max_filename_len;
>  
> -	if (filename_len >= sizeof(ev.mmap2.filename))
> -		return -EINVAL;
> +	max_filename_len = sizeof(ev) -
> +			   (MAX_ID_HDR_ENTRIES * sizeof(__u64)) -
> +			   offsetof(struct perf_record_mmap2, filename) - 1;

[Severity: Medium]
Will this calculation cause an issue if the size of the union perf_event
ever grows larger than struct perf_record_mmap2?

Since max_filename_len is derived from sizeof(ev) rather than the capacity of
the ev.mmap2.filename array, any future expansion of the union could cause
max_filename_len to exceed the actual array bounds.

>  
> -	ev_len = sizeof(ev.mmap2) - sizeof(ev.mmap2.filename) + filename_len + 1;
> +	if (filename_len > max_filename_len)
> +		filename_len = max_filename_len;
> +
> +	ev_len = offsetof(struct perf_record_mmap2, filename) + filename_len + 1;
>  	ev_len = PERF_ALIGN(ev_len, sizeof(u64));
[ ... ]
> @@ -2474,16 +2479,15 @@ int perf_event__synthesize_mmap2_build_id(const struct perf_tool *tool,
[ ... ]
> -	memcpy(ev.mmap2.filename, filename, min(strlen(filename), sizeof(ev.mmap.filename)));
> +	strlcpy(ev.mmap2.filename, filename, filename_len + 1);

[Severity: Medium]
If filename_len is bounded by sizeof(ev) and the union expands, could this
strlcpy write past the ev.mmap2.filename array capacity and trigger a
_FORTIFY_SOURCE abort?

When built with _FORTIFY_SOURCE=2, bounds checks evaluate against the sub-object
array capacity (ev.mmap2.filename) rather than the enclosing struct.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721182150.94016-1-irogers@google.com?part=4

Re: [PATCH v4 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

New issues:
- [Critical] Bypassing _FORTIFY_SOURCE array bounds checks introduces an exploitable stack buffer overflow when zeroing event trailers.
- [High] Removal of the stale build ID clearing leaks state and corrupts subsequent kernel module events.

Pre-existing issues:
- [High] Incomplete fix: _FORTIFY_SOURCE array bounds aborts still exist in multiple other synthesis functions.
--

--- Patch [2]: [PATCH v4 2/4] perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader ---
commit ba0b89af1798a9c26d45cb174748a43558ce4d9d
Author: Ian Rogers <irogers@google.com>

perf synthetic-events: Fix line synchronization, bounds, and truncation bugs in proc maps reader

This commit fixes bugs in read_proc_maps_line() and its callers by ensuring
proper line draining on parsing failures. It also adds standard fallbacks
for over-length paths, safely emits timeout flags, and introduces pointer
casts to prevent _FORTIFY_SOURCE array bounds aborts when zeroing trailers.

> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 5307d707711d8..e0680d770462c 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
[ ... ]
> @@ -463,45 +533,53 @@ int perf_event__synthesize_mmap_events(const struct perf_tool *tool,
[ ... ]
> -		memset(event->mmap2.filename + size, 0, machine->id_hdr_size +
> -			(aligned_size - size));
> -		event->mmap2.header.size += machine->id_hdr_size;
> +		/* Zero the padding and ID header trailer safely! */
> +		memset((char *)event + offsetof(struct perf_record_mmap2, filename) + size, 0,
> +		       (aligned_size - size) + machine->id_hdr_size);
> +
> +		event->mmap2.header.size += machine->id_hdr_size;

[Severity: Critical]
Can bypassing the _FORTIFY_SOURCE array bounds checks introduce a stack
buffer overflow regression here?

When this function is called via machine__init_live(), the event union is
allocated on the stack without the extra padding for id_hdr_size:

tools/perf/util/machine.c:machine__init_live() {
    union perf_event event;
    memset(&event, 0, sizeof(event));
    ...
    perf_event__synthesize_mmap_events(tool, &event, ...);
}

If an attacker provides a pathname approaching PATH_MAX in /proc/pid/maps,
size pushes the memset destination to the end of the union perf_event
structure. By bypassing the fortify check, this memset blindly writes
machine->id_hdr_size bytes of zeroes completely outside the bounds of the
stack variable, silently corrupting the stack frame instead of safely
aborting.

[Severity: High]
This is a pre-existing issue, but does the same _FORTIFY_SOURCE array
bounds abort regression still exist in other synthesis functions?

While this patch applies a cast bypass here in
perf_event__synthesize_mmap_events(), similar bounds-violating memset calls
remain in other paths. 

For example, in perf_event__prepare_comm():

tools/perf/util/synthetic-events.c:perf_event__prepare_comm() {
    ...
    memset(event->comm.comm + size, 0, machine->id_hdr_size);
    ...
}

Since event->comm.comm is a static 16-byte array, if a process name is 15
characters long, the memset begins exactly at the end of the array and
writes id_hdr_size bytes. Under modern compiler flags (_FORTIFY_SOURCE=2
or 3), this reliably triggers an abort because the compiler detects
the memset writing past the bounds of the array. The same pattern is
also present in perf_event__synthesize_cgroups().

[ ... ]
> @@ -703,11 +781,6 @@ static int perf_event__synthesize_modules_maps_cb(struct map *map, void *data)
>  
>  		memcpy(event->mmap2.filename, dso__long_name(dso), dso__long_name_len(dso) + 1);
>  
> -		/* Clear stale build ID from previous module iteration */
> -		event->mmap2.header.misc &= ~PERF_RECORD_MISC_MMAP_BUILD_ID;
> -		memset(event->mmap2.build_id, 0, sizeof(event->mmap2.build_id));
> -		event->mmap2.build_id_size = 0;
> -
>  		perf_record_mmap2__read_build_id(&event->mmap2, args->machine, false);
>  	} else {
>  		size = PERF_ALIGN(dso__long_name_len(dso) + 1, sizeof(u64));

[Severity: High]
Could removing this explicit clearing of the shared union's build ID leak
state between loop iterations?

The perf_event__synthesize_modules() function allocates a single
union perf_event structure outside the loop and reuses it for every kernel
module via maps__for_each_map().

By removing the explicit clearing of PERF_RECORD_MISC_MMAP_BUILD_ID, if one
module successfully reads a build ID, the flag remains set for all
subsequent modules.

When processing subsequent modules, perf_record_mmap2__read_build_id() sees
the flag is already set, assumes the event already contains a valid build
ID, and reads the stale build ID from the previous iteration. This could
attribute samples to incorrect binaries.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721182150.94016-1-irogers@google.com?part=2