| Message ID | 20220425090841.3958494-3-atomlin@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | module: Introduce module unload taint tracking | expand |
Le 25/04/2022 à 11:08, Aaron Tomlin a écrit : > 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/main.c | 65 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 76 insertions(+) > > 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/main.c b/kernel/module/main.c > index ea78cec316dd..35686e63b32f 100644 > --- a/kernel/module/main.c > +++ b/kernel/module/main.c > @@ -68,6 +68,16 @@ > */ > DEFINE_MUTEX(module_mutex); > LIST_HEAD(modules); > +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING > +static LIST_HEAD(unloaded_tainted_modules); > + > +struct mod_unload_taint { > + struct list_head list; > + char name[MODULE_NAME_LEN]; > + unsigned long taints; > + u64 count; > +}; > +#endif > > /* Work queue for freeing init sections in success case */ > static void do_free_init(struct work_struct *w); > @@ -150,6 +160,41 @@ int unregister_module_notifier(struct notifier_block *nb) > } > EXPORT_SYMBOL(unregister_module_notifier); > > +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING > +static 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)) { > + size_t len = strlen(mod_taint->name); Why do you need that strlen() at all, can't you just use strcmp() ? With strncmp() what happens if for instance mod_taint->name is "dead" and mod->name is "deadbeef" ? > + > + if (!strncmp(mod_taint->name, mod->name, len) && > + 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; > +} > +#else /* MODULE_UNLOAD_TAINT_TRACKING */ > +static int try_add_tainted_module(struct module *mod) > +{ > + return 0; > +} > +#endif > + > /* > * We require a truly strong try_module_get(): 0 means success. > * Otherwise an error is returned due to ongoing or failed > @@ -1201,6 +1246,9 @@ 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. */ > @@ -3126,6 +3174,9 @@ struct module *__module_text_address(unsigned long addr) > void print_modules(void) > { > struct module *mod; > +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING > + struct mod_unload_taint *mod_taint; > +#endif > char buf[MODULE_FLAGS_BUF_SIZE]; > > printk(KERN_DEFAULT "Modules linked in:"); > @@ -3136,6 +3187,20 @@ void print_modules(void) > continue; > pr_cont(" %s%s", mod->name, module_flags(mod, buf)); > } > +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING > + 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); > + } > + } > +#endif > preempt_enable(); > if (last_unloaded_module[0]) > pr_cont(" [last unloaded: %s]", last_unloaded_module);
On Mon 2022-05-02 11:07 +0000, Christophe Leroy wrote: > > @@ -150,6 +160,41 @@ int unregister_module_notifier(struct notifier_block *nb) > > } > > EXPORT_SYMBOL(unregister_module_notifier); > > > > +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING > > +static 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)) { > > + size_t len = strlen(mod_taint->name); > > Why do you need that strlen() at all, can't you just use strcmp() ? > With strncmp() what happens if for instance mod_taint->name is "dead" > and mod->name is "deadbeef" ? Hi Christophe, Thanks for your feedback. I see that. Furthermore, the length of a module's name is fixed. Hence strcmp() should be fine. Kind regards,
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/main.c b/kernel/module/main.c index ea78cec316dd..35686e63b32f 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -68,6 +68,16 @@ */ DEFINE_MUTEX(module_mutex); LIST_HEAD(modules); +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING +static LIST_HEAD(unloaded_tainted_modules); + +struct mod_unload_taint { + struct list_head list; + char name[MODULE_NAME_LEN]; + unsigned long taints; + u64 count; +}; +#endif /* Work queue for freeing init sections in success case */ static void do_free_init(struct work_struct *w); @@ -150,6 +160,41 @@ int unregister_module_notifier(struct notifier_block *nb) } EXPORT_SYMBOL(unregister_module_notifier); +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING +static 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)) { + size_t len = strlen(mod_taint->name); + + if (!strncmp(mod_taint->name, mod->name, len) && + 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; +} +#else /* MODULE_UNLOAD_TAINT_TRACKING */ +static int try_add_tainted_module(struct module *mod) +{ + return 0; +} +#endif + /* * We require a truly strong try_module_get(): 0 means success. * Otherwise an error is returned due to ongoing or failed @@ -1201,6 +1246,9 @@ 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. */ @@ -3126,6 +3174,9 @@ struct module *__module_text_address(unsigned long addr) void print_modules(void) { struct module *mod; +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING + struct mod_unload_taint *mod_taint; +#endif char buf[MODULE_FLAGS_BUF_SIZE]; printk(KERN_DEFAULT "Modules linked in:"); @@ -3136,6 +3187,20 @@ void print_modules(void) continue; pr_cont(" %s%s", mod->name, module_flags(mod, buf)); } +#ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING + 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); + } + } +#endif preempt_enable(); if (last_unloaded_module[0]) pr_cont(" [last unloaded: %s]", last_unloaded_module);
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/main.c | 65 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 76 insertions(+)