[PATCH v5 3/3] module: Introduce module unload taint tracking

Aaron Tomlin
2022-05-02T20:53:12Z

Currently, only the initial module that tainted the kernel is
recorded e.g. when an out-of-tree module is loaded.

The purpose of this patch is to allow the kernel to maintain a record of
each unloaded module that taints the kernel. So, in addition to
displaying a list of linked modules (see print_modules()) e.g. in the
event of a detected bad page, unloaded modules that carried a taint/or
taints are displayed too. A tainted module unload count is maintained.

The number of tracked modules is not fixed. This feature is disabled by
default.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
---
init/Kconfig | 11 ++++++++
kernel/module/Makefile | 1 +
kernel/module/internal.h | 21 ++++++++++++++
kernel/module/main.c | 5 ++++
kernel/module/tracking.c | 61 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 99 insertions(+)
create mode 100644 kernel/module/tracking.c

diff --git a/init/Kconfig b/init/Kconfig
index ddcbefe535e9..6b30210f787d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2118,6 +2118,17 @@ config MODULE_FORCE_UNLOAD
rmmod). This is mainly for kernel developers and desperate users.
If unsure, say N.

+config MODULE_UNLOAD_TAINT_TRACKING
+ bool "Tainted module unload tracking"
+ depends on MODULE_UNLOAD
+ default n
+ help
+ This option allows you to maintain a record of each unloaded
+ module that tainted the kernel. In addition to displaying a
+ list of linked (or loaded) modules e.g. on detection of a bad
+ page (see bad_page()), the aforementioned details are also
+ shown. If unsure, say N.
+
config MODVERSIONS
bool "Module versioning support"
help
diff --git a/kernel/module/Makefile b/kernel/module/Makefile
index d1ca799c12e2..948efea81e85 100644
--- a/kernel/module/Makefile
+++ b/kernel/module/Makefile
@@ -18,3 +18,4 @@ obj-$(CONFIG_PROC_FS) += procfs.o
obj-$(CONFIG_SYSFS) += sysfs.o
obj-$(CONFIG_KGDB_KDB) += kdb.o
obj-$(CONFIG_MODVERSIONS) += version.o
+obj-$(CONFIG_MODULE_UNLOAD_TAINT_TRACKING) += tracking.o
diff --git a/kernel/module/internal.h b/kernel/module/internal.h
index 0bdf64c9dfb5..bc5507ab8450 100644
--- a/kernel/module/internal.h
+++ b/kernel/module/internal.h
@@ -145,6 +145,27 @@ static inline bool set_livepatch_module(struct module *mod)
#endif
}

+#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING
+struct mod_unload_taint {
+ struct list_head list;
+ char name[MODULE_NAME_LEN];
+ unsigned long taints;
+ u64 count;
+};
+
+int try_add_tainted_module(struct module *mod);
+void print_unloaded_tainted_modules(void);
+#else /* !CONFIG_MODULE_UNLOAD_TAINT_TRACKING */
+static inline int try_add_tainted_module(struct module *mod)
+{
+ return 0;
+}
+
+static inline void print_unloaded_tainted_modules(void)
+{
+}
+#endif /* CONFIG_MODULE_UNLOAD_TAINT_TRACKING */
+
#ifdef CONFIG_MODULE_DECOMPRESS
int module_decompress(struct load_info *info, const void *buf, size_t size);
void module_decompress_cleanup(struct load_info *info);
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 7a0484900320..6c3b4a846645 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1190,6 +1190,9 @@ static void free_module(struct module *mod)
module_bug_cleanup(mod);
/* Wait for RCU-sched synchronizing before releasing mod->list and buglist. */
synchronize_rcu();
+ if (try_add_tainted_module(mod))
+ pr_err("%s: adding tainted module to the unloaded tainted modules list failed.\n",
+ mod->name);
mutex_unlock(&module_mutex);

/* Clean up CFI for the module. */
@@ -3125,6 +3128,8 @@ void print_modules(void)
continue;
pr_cont(" %s%s", mod->name, module_flags(mod, buf));
}
+
+ print_unloaded_tainted_modules();
preempt_enable();
if (last_unloaded_module[0])
pr_cont(" [last unloaded: %s]", last_unloaded_module);
diff --git a/kernel/module/tracking.c b/kernel/module/tracking.c
new file mode 100644
index 000000000000..7f8133044d09
--- /dev/null
+++ b/kernel/module/tracking.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Module taint unload tracking support
+ *
+ * Copyright (C) 2022 Aaron Tomlin
+ */
+
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/rculist.h>
+#include "internal.h"
+
+static LIST_HEAD(unloaded_tainted_modules);
+
+int try_add_tainted_module(struct module *mod)
+{
+ struct mod_unload_taint *mod_taint;
+
+ module_assert_mutex_or_preempt();
+
+ list_for_each_entry_rcu(mod_taint, &unloaded_tainted_modules, list,
+ lockdep_is_held(&module_mutex)) {
+ if (!strcmp(mod_taint->name, mod->name) &&
+ mod_taint->taints & mod->taints) {
+ mod_taint->count++;
+ goto out;
+ }
+ }
+
+ mod_taint = kmalloc(sizeof(*mod_taint), GFP_KERNEL);
+ if (unlikely(!mod_taint))
+ return -ENOMEM;
+ strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN);
+ mod_taint->taints = mod->taints;
+ list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
+ mod_taint->count = 1;
+out:
+ return 0;
+}
+
+void print_unloaded_tainted_modules(void)
+{
+ struct mod_unload_taint *mod_taint;
+ char buf[MODULE_FLAGS_BUF_SIZE];
+
+ if (!list_empty(&unloaded_tainted_modules)) {
+ printk(KERN_DEFAULT "Unloaded tainted modules:");
+ list_for_each_entry_rcu(mod_taint, &unloaded_tainted_modules,
+ list) {
+ size_t l;
+
+ l = module_flags_taint(mod_taint->taints, buf);
+ buf[l++] = '\0';
+ pr_cont(" %s(%s):%llu", mod_taint->name, buf,
+ mod_taint->count);
+ }
+ }
+}
--
2.34.1