[PATCH v3] perf dso: Fix kallsyms DSO detection with fallback logic
From: Tanushree Shah <hidden>
Date: 2026-06-26 16:12:00
Also in:
linux-perf-users
Subsystem:
performance events subsystem, the rest · Maintainers:
Peter Zijlstra, Ingo Molnar, Arnaldo Carvalho de Melo, Namhyung Kim, Linus Torvalds
The current kallsyms detection in dso__is_kallsyms() uses the
dso_binary_type enum which fixes the issue of kallsyms being cached in
the build-id cache for out-of-tree modules.
However, during build-id injection in perf record/inject, dso_binary_type
has not been explicitly set yet,so dso__binary_type() returns
DSO_BINARY_TYPE__NOT_FOUND instead of DSO_BINARY_TYPE__KALLSYMS for the
kernel DSO. The current check then fails to identify it as kallsyms,
causing build-id symlinks to not be created in ~/.debug/.build-id/ and
perf archive to fail with "Cannot stat" errors.
Steps to reproduce the issue:
1. rm -rf ~/.debug/.build-id
2. perf record sleep 1
3. perf archive
Fix by falling back to matching long_name against the known kallsyms
strings explicitly when binary_type is not yet set
(== DSO_BINARY_TYPE__NOT_FOUND). Use strcmp() for exact matching of
fixed names and strict validation for guest kallsyms with embedded PID
to prevent path traversal attacks.
Fixes: ebf0b332732d ("perf dso: fix dso__is_kallsyms() check")
Signed-off-by: Tanushree Shah <redacted>
---
v2 -> v3: Replace strncmp() prefix matching with strcmp() for fixed
kallsyms names and add is_guest_kallsyms_pid_name() to
strictly validate guest kallsyms with PID format, preventing
path traversal attacks.
v1 -> v2: Rename DSO__NAME_GUEST_KALLSYMS to DSO__PREFIX_GUEST_KALLSYMS
to reflect that it is a prefix, not a full name.
v1: https://lore.kernel.org/all/20260410071225.708005-2-tshah@linux.ibm.com/ (local)
tools/perf/util/dso.h | 57 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 56 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index ede691e9a249..8763e6f65316 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h@@ -9,6 +9,7 @@ #include <stdbool.h> #include <stdio.h> #include <linux/bitops.h> +#include <string.h> #include "build-id.h" #include "debuginfo.h" #include "mutex.h"
@@ -20,6 +21,40 @@ struct perf_env; #define DSO__NAME_KALLSYMS "[kernel.kallsyms]" #define DSO__NAME_KCORE "[kernel.kcore]" +#define DSO__NAME_GUEST_KALLSYMS "[guest.kernel.kallsyms]" +#define DSO__NAME_GUEST_KALLSYMS_PID_PREFIX "[guest.kernel.kallsyms." + +/* + * Validate names of the form "[guest.kernel.kallsyms.<pid>]", where + * <pid> is the PID of the guest VM and varies per guest, so it + * cannot be matched with strcmp() against a fixed string. + * + * Every character after the fixed prefix must be a decimal digit, + * with ']' immediately terminating the digit run and nothing + * following it. This rules out '/', "..", or any other character + * being smuggled into the name. + */ +static inline bool is_guest_kallsyms_pid_name(const char *name) +{ + const size_t prefix_len = sizeof(DSO__NAME_GUEST_KALLSYMS_PID_PREFIX) - 1; + size_t digits; + + if (strncmp(name, DSO__NAME_GUEST_KALLSYMS_PID_PREFIX, prefix_len) != 0) + return false; + + digits = strspn(name + prefix_len, "0123456789"); + if (digits == 0) + return false; + + /* ']' must terminate the digit run, with nothing trailing it */ + if (name[prefix_len + digits] != ']') + return false; + + if (name[prefix_len + digits + 1] != '\0') + return false; + + return true; +} /** * enum dso_binary_type - The kind of DSO generally associated with a memory
@@ -914,8 +949,28 @@ static inline bool dso__is_kcore(const struct dso *dso) static inline bool dso__is_kallsyms(const struct dso *dso) { enum dso_binary_type bt = dso__binary_type(dso); + const char *name; + + if (bt == DSO_BINARY_TYPE__KALLSYMS || bt == DSO_BINARY_TYPE__GUEST_KALLSYMS) + return true; + + if (bt != DSO_BINARY_TYPE__NOT_FOUND) + return false; + + if (!RC_CHK_ACCESS(dso)->kernel) + return false; + + name = RC_CHK_ACCESS(dso)->long_name; + if (!name) + return false; + + if (!strcmp(name, DSO__NAME_KALLSYMS)) + return true; + + if (!strcmp(name, DSO__NAME_GUEST_KALLSYMS)) + return true; - return bt == DSO_BINARY_TYPE__KALLSYMS || bt == DSO_BINARY_TYPE__GUEST_KALLSYMS; + return is_guest_kallsyms_pid_name(name); } bool dso__is_object_file(const struct dso *dso);
--
2.47.3