[PATCH v8 1/5] add infrastructure for tagging functions as error injectable

From: Josef Bacik
Date: Wed Dec 06 2017 - 11:12:55 EST

From: Josef Bacik <jbacik@xxxxxx>

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@xxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/asm-generic/vmlinux.lds.h | 10 +++
include/linux/bpf.h | 11 +++
include/linux/kprobes.h | 1 +
include/linux/module.h | 5 ++
kernel/kprobes.c | 163 ++++++++++++++++++++++++++++++++++++++
kernel/module.c | 6 +-
6 files changed, 195 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8acfc1e099e1..85822804861e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -136,6 +136,15 @@
#define KPROBE_BLACKLIST()
#endif

+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+#define ERROR_INJECT_LIST() . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start_kprobe_error_inject_list) = .; \
+ KEEP(*(_kprobe_error_inject_list)) \
+ VMLINUX_SYMBOL(__stop_kprobe_error_inject_list) = .;
+#else
+#define ERROR_INJECT_LIST()
+#endif
+
#ifdef CONFIG_EVENT_TRACING
#define FTRACE_EVENTS() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_ftrace_events) = .; \
@@ -560,6 +569,7 @@
FTRACE_EVENTS() \
TRACE_SYSCALLS() \
KPROBE_BLACKLIST() \
+ ERROR_INJECT_LIST() \
MEM_DISCARD(init.rodata) \
CLK_OF_TABLES() \
RESERVEDMEM_OF_TABLES() \
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 520aeebe0d93..552a666a338b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -530,4 +530,15 @@ extern const struct bpf_func_proto bpf_sock_map_update_proto;
void bpf_user_rnd_init_once(void);
u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);

+#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+#define BPF_ALLOW_ERROR_INJECTION(fname) \
+static unsigned long __used \
+ __attribute__((__section__("_kprobe_error_inject_list"))) \
+ _eil_addr_##fname = (unsigned long)fname;
+#else
+#define BPF_ALLOW_ERROR_INJECTION(fname)
+#endif
+#endif
+
#endif /* _LINUX_BPF_H */
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index bd2684700b74..4f501cb73aec 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -271,6 +271,7 @@ extern bool arch_kprobe_on_func_entry(unsigned long offset);
extern bool kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset);

extern bool within_kprobe_blacklist(unsigned long addr);
+extern bool within_kprobe_error_injection_list(unsigned long addr);

struct kprobe_insn_cache {
struct mutex mutex;
diff --git a/include/linux/module.h b/include/linux/module.h
index fe5aa3736707..7bb1a9b9a322 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -475,6 +475,11 @@ struct module {
ctor_fn_t *ctors;
unsigned int num_ctors;
#endif
+
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+ unsigned int num_kprobe_ei_funcs;
+ unsigned long *kprobe_ei_funcs;
+#endif
} ____cacheline_aligned __randomize_layout;
#ifndef MODULE_ARCH_INIT
#define MODULE_ARCH_INIT {}
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index a1606a4224e1..bdd7dd724f6f 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -83,6 +83,16 @@ static raw_spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
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);

@@ -1392,6 +1402,17 @@ bool within_kprobe_blacklist(unsigned long addr)
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.
@@ -2164,6 +2185,86 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
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)
@@ -2174,6 +2275,11 @@ static int kprobes_module_callback(struct notifier_block *nb,
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;

@@ -2236,6 +2342,8 @@ static int __init init_kprobes(void)
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++) {
@@ -2403,6 +2511,56 @@ static const struct file_operations debugfs_kprobe_blacklist_ops = {
.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;
@@ -2544,6 +2702,11 @@ static int __init debugfs_kprobe_init(void)
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 de66ec825992..19d8d9455f2f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3110,7 +3110,11 @@ static int find_module_sections(struct module *mod, struct load_info *info)
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);

--
2.7.5