add infrastructure for tagging functions as error injectable
Using BPF we can override kprob'ed functions and return arbitrary
values. Obviously this can be a bit unsafe, so make this feature opt-in
for functions. Simply tag a function with KPROBE_ERROR_INJECT_SYMBOL in
order to give BPF access to that function for error injection purposes.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index da2ccf1..b4aab48 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -83,6 +83,16 @@
return &(kretprobe_table_locks[hash].lock);
}
+/* List of symbols that can be overriden for error injection. */
+static LIST_HEAD(kprobe_error_injection_list);
+static DEFINE_MUTEX(kprobe_ei_mutex);
+struct kprobe_ei_entry {
+ struct list_head list;
+ unsigned long start_addr;
+ unsigned long end_addr;
+ void *priv;
+};
+
/* Blacklist -- list of struct kprobe_blacklist_entry */
static LIST_HEAD(kprobe_blacklist);
@@ -1394,6 +1404,17 @@
return false;
}
+bool within_kprobe_error_injection_list(unsigned long addr)
+{
+ struct kprobe_ei_entry *ent;
+
+ list_for_each_entry(ent, &kprobe_error_injection_list, list) {
+ if (addr >= ent->start_addr && addr < ent->end_addr)
+ return true;
+ }
+ return false;
+}
+
/*
* If we have a symbol_name argument, look it up and add the offset field
* to it. This way, we can specify a relative address to a symbol.
@@ -2168,6 +2189,86 @@
return 0;
}
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+/* Markers of the _kprobe_error_inject_list section */
+extern unsigned long __start_kprobe_error_inject_list[];
+extern unsigned long __stop_kprobe_error_inject_list[];
+
+/*
+ * Lookup and populate the kprobe_error_injection_list.
+ *
+ * For safety reasons we only allow certain functions to be overriden with
+ * bpf_error_injection, so we need to populate the list of the symbols that have
+ * been marked as safe for overriding.
+ */
+static void populate_kprobe_error_injection_list(unsigned long *start,
+ unsigned long *end,
+ void *priv)
+{
+ unsigned long *iter;
+ struct kprobe_ei_entry *ent;
+ unsigned long entry, offset = 0, size = 0;
+
+ mutex_lock(&kprobe_ei_mutex);
+ for (iter = start; iter < end; iter++) {
+ entry = arch_deref_entry_point((void *)*iter);
+
+ if (!kernel_text_address(entry) ||
+ !kallsyms_lookup_size_offset(entry, &size, &offset)) {
+ pr_err("Failed to find error inject entry at %p\n",
+ (void *)entry);
+ continue;
+ }
+
+ ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+ if (!ent)
+ break;
+ ent->start_addr = entry;
+ ent->end_addr = entry + size;
+ ent->priv = priv;
+ INIT_LIST_HEAD(&ent->list);
+ list_add_tail(&ent->list, &kprobe_error_injection_list);
+ }
+ mutex_unlock(&kprobe_ei_mutex);
+}
+
+static void __init populate_kernel_kprobe_ei_list(void)
+{
+ populate_kprobe_error_injection_list(__start_kprobe_error_inject_list,
+ __stop_kprobe_error_inject_list,
+ NULL);
+}
+
+static void module_load_kprobe_ei_list(struct module *mod)
+{
+ if (!mod->num_kprobe_ei_funcs)
+ return;
+ populate_kprobe_error_injection_list(mod->kprobe_ei_funcs,
+ mod->kprobe_ei_funcs +
+ mod->num_kprobe_ei_funcs, mod);
+}
+
+static void module_unload_kprobe_ei_list(struct module *mod)
+{
+ struct kprobe_ei_entry *ent, *n;
+ if (!mod->num_kprobe_ei_funcs)
+ return;
+
+ mutex_lock(&kprobe_ei_mutex);
+ list_for_each_entry_safe(ent, n, &kprobe_error_injection_list, list) {
+ if (ent->priv == mod) {
+ list_del_init(&ent->list);
+ kfree(ent);
+ }
+ }
+ mutex_unlock(&kprobe_ei_mutex);
+}
+#else
+static inline void __init populate_kernel_kprobe_ei_list(void) {}
+static inline void module_load_kprobe_ei_list(struct module *m) {}
+static inline void module_unload_kprobe_ei_list(struct module *m) {}
+#endif
+
/* Module notifier call back, checking kprobes on the module */
static int kprobes_module_callback(struct notifier_block *nb,
unsigned long val, void *data)
@@ -2178,6 +2279,11 @@
unsigned int i;
int checkcore = (val == MODULE_STATE_GOING);
+ if (val == MODULE_STATE_COMING)
+ module_load_kprobe_ei_list(mod);
+ else if (val == MODULE_STATE_GOING)
+ module_unload_kprobe_ei_list(mod);
+
if (val != MODULE_STATE_GOING && val != MODULE_STATE_LIVE)
return NOTIFY_DONE;
@@ -2240,6 +2346,8 @@
pr_err("Please take care of using kprobes.\n");
}
+ populate_kernel_kprobe_ei_list();
+
if (kretprobe_blacklist_size) {
/* lookup the function address from its name */
for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
@@ -2407,6 +2515,56 @@
.release = seq_release,
};
+/*
+ * kprobes/error_injection_list -- shows which functions can be overriden for
+ * error injection.
+ * */
+static void *kprobe_ei_seq_start(struct seq_file *m, loff_t *pos)
+{
+ mutex_lock(&kprobe_ei_mutex);
+ return seq_list_start(&kprobe_error_injection_list, *pos);
+}
+
+static void kprobe_ei_seq_stop(struct seq_file *m, void *v)
+{
+ mutex_unlock(&kprobe_ei_mutex);
+}
+
+static void *kprobe_ei_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+ return seq_list_next(v, &kprobe_error_injection_list, pos);
+}
+
+static int kprobe_ei_seq_show(struct seq_file *m, void *v)
+{
+ char buffer[KSYM_SYMBOL_LEN];
+ struct kprobe_ei_entry *ent =
+ list_entry(v, struct kprobe_ei_entry, list);
+
+ sprint_symbol(buffer, ent->start_addr);
+ seq_printf(m, "%s\n", buffer);
+ return 0;
+}
+
+static const struct seq_operations kprobe_ei_seq_ops = {
+ .start = kprobe_ei_seq_start,
+ .next = kprobe_ei_seq_next,
+ .stop = kprobe_ei_seq_stop,
+ .show = kprobe_ei_seq_show,
+};
+
+static int kprobe_ei_open(struct inode *inode, struct file *filp)
+{
+ return seq_open(filp, &kprobe_ei_seq_ops);
+}
+
+static const struct file_operations debugfs_kprobe_ei_ops = {
+ .open = kprobe_ei_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
static void arm_all_kprobes(void)
{
struct hlist_head *head;
@@ -2548,6 +2706,11 @@
if (!file)
goto error;
+ file = debugfs_create_file("error_injection_list", 0444, dir, NULL,
+ &debugfs_kprobe_ei_ops);
+ if (!file)
+ goto error;
+
return 0;
error:
diff --git a/kernel/module.c b/kernel/module.c
index dea01ac..bd695bf 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3118,7 +3118,11 @@
sizeof(*mod->ftrace_callsites),
&mod->num_ftrace_callsites);
#endif
-
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+ mod->kprobe_ei_funcs = section_objs(info, "_kprobe_error_inject_list",
+ sizeof(*mod->kprobe_ei_funcs),
+ &mod->num_kprobe_ei_funcs);
+#endif
mod->extable = section_objs(info, "__ex_table",
sizeof(*mod->extable), &mod->num_exentries);