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-rw-r--r--kernel/bpf/verifier.c146
1 files changed, 146 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a086dd3210a8..801f5f3b9307 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -199,6 +199,7 @@ struct verifier_env {
struct verifier_stack_elem *head; /* stack of verifier states to be processed */
int stack_size; /* number of states to be processed */
struct verifier_state cur_state; /* current verifier state */
+ struct verifier_state_list **explored_states; /* search pruning optimization */
struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
u32 used_map_cnt; /* number of used maps */
};
@@ -1219,6 +1220,8 @@ enum {
BRANCH = 2,
};
+#define STATE_LIST_MARK ((struct verifier_state_list *) -1L)
+
static int *insn_stack; /* stack of insns to process */
static int cur_stack; /* current stack index */
static int *insn_state;
@@ -1241,6 +1244,10 @@ static int push_insn(int t, int w, int e, struct verifier_env *env)
return -EINVAL;
}
+ if (e == BRANCH)
+ /* mark branch target for state pruning */
+ env->explored_states[w] = STATE_LIST_MARK;
+
if (insn_state[w] == 0) {
/* tree-edge */
insn_state[t] = DISCOVERED | e;
@@ -1314,6 +1321,10 @@ peek_stack:
goto peek_stack;
else if (ret < 0)
goto err_free;
+ /* tell verifier to check for equivalent states
+ * after every call and jump
+ */
+ env->explored_states[t + 1] = STATE_LIST_MARK;
} else {
/* conditional jump with two edges */
ret = push_insn(t, t + 1, FALLTHROUGH, env);
@@ -1364,6 +1375,95 @@ err_free:
return ret;
}
+/* compare two verifier states
+ *
+ * all states stored in state_list are known to be valid, since
+ * verifier reached 'bpf_exit' instruction through them
+ *
+ * this function is called when verifier exploring different branches of
+ * execution popped from the state stack. If it sees an old state that has
+ * more strict register state and more strict stack state then this execution
+ * branch doesn't need to be explored further, since verifier already
+ * concluded that more strict state leads to valid finish.
+ *
+ * Therefore two states are equivalent if register state is more conservative
+ * and explored stack state is more conservative than the current one.
+ * Example:
+ * explored current
+ * (slot1=INV slot2=MISC) == (slot1=MISC slot2=MISC)
+ * (slot1=MISC slot2=MISC) != (slot1=INV slot2=MISC)
+ *
+ * In other words if current stack state (one being explored) has more
+ * valid slots than old one that already passed validation, it means
+ * the verifier can stop exploring and conclude that current state is valid too
+ *
+ * Similarly with registers. If explored state has register type as invalid
+ * whereas register type in current state is meaningful, it means that
+ * the current state will reach 'bpf_exit' instruction safely
+ */
+static bool states_equal(struct verifier_state *old, struct verifier_state *cur)
+{
+ int i;
+
+ for (i = 0; i < MAX_BPF_REG; i++) {
+ if (memcmp(&old->regs[i], &cur->regs[i],
+ sizeof(old->regs[0])) != 0) {
+ if (old->regs[i].type == NOT_INIT ||
+ old->regs[i].type == UNKNOWN_VALUE)
+ continue;
+ return false;
+ }
+ }
+
+ for (i = 0; i < MAX_BPF_STACK; i++) {
+ if (memcmp(&old->stack[i], &cur->stack[i],
+ sizeof(old->stack[0])) != 0) {
+ if (old->stack[i].stype == STACK_INVALID)
+ continue;
+ return false;
+ }
+ }
+ return true;
+}
+
+static int is_state_visited(struct verifier_env *env, int insn_idx)
+{
+ struct verifier_state_list *new_sl;
+ struct verifier_state_list *sl;
+
+ sl = env->explored_states[insn_idx];
+ if (!sl)
+ /* this 'insn_idx' instruction wasn't marked, so we will not
+ * be doing state search here
+ */
+ return 0;
+
+ while (sl != STATE_LIST_MARK) {
+ if (states_equal(&sl->state, &env->cur_state))
+ /* reached equivalent register/stack state,
+ * prune the search
+ */
+ return 1;
+ sl = sl->next;
+ }
+
+ /* there were no equivalent states, remember current one.
+ * technically the current state is not proven to be safe yet,
+ * but it will either reach bpf_exit (which means it's safe) or
+ * it will be rejected. Since there are no loops, we won't be
+ * seeing this 'insn_idx' instruction again on the way to bpf_exit
+ */
+ new_sl = kmalloc(sizeof(struct verifier_state_list), GFP_USER);
+ if (!new_sl)
+ return -ENOMEM;
+
+ /* add new state to the head of linked list */
+ memcpy(&new_sl->state, &env->cur_state, sizeof(env->cur_state));
+ new_sl->next = env->explored_states[insn_idx];
+ env->explored_states[insn_idx] = new_sl;
+ return 0;
+}
+
static int do_check(struct verifier_env *env)
{
struct verifier_state *state = &env->cur_state;
@@ -1396,6 +1496,21 @@ static int do_check(struct verifier_env *env)
return -E2BIG;
}
+ err = is_state_visited(env, insn_idx);
+ if (err < 0)
+ return err;
+ if (err == 1) {
+ /* found equivalent state, can prune the search */
+ if (log_level) {
+ if (do_print_state)
+ verbose("\nfrom %d to %d: safe\n",
+ prev_insn_idx, insn_idx);
+ else
+ verbose("%d: safe\n", insn_idx);
+ }
+ goto process_bpf_exit;
+ }
+
if (log_level && do_print_state) {
verbose("\nfrom %d to %d:", prev_insn_idx, insn_idx);
print_verifier_state(env);
@@ -1531,6 +1646,7 @@ static int do_check(struct verifier_env *env)
if (err)
return err;
+process_bpf_exit:
insn_idx = pop_stack(env, &prev_insn_idx);
if (insn_idx < 0) {
break;
@@ -1671,6 +1787,28 @@ static void convert_pseudo_ld_imm64(struct verifier_env *env)
insn->src_reg = 0;
}
+static void free_states(struct verifier_env *env)
+{
+ struct verifier_state_list *sl, *sln;
+ int i;
+
+ if (!env->explored_states)
+ return;
+
+ for (i = 0; i < env->prog->len; i++) {
+ sl = env->explored_states[i];
+
+ if (sl)
+ while (sl != STATE_LIST_MARK) {
+ sln = sl->next;
+ kfree(sl);
+ sl = sln;
+ }
+ }
+
+ kfree(env->explored_states);
+}
+
int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
{
char __user *log_ubuf = NULL;
@@ -1719,6 +1857,13 @@ int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
if (ret < 0)
goto skip_full_check;
+ env->explored_states = kcalloc(prog->len,
+ sizeof(struct verifier_state_list *),
+ GFP_USER);
+ ret = -ENOMEM;
+ if (!env->explored_states)
+ goto skip_full_check;
+
ret = check_cfg(env);
if (ret < 0)
goto skip_full_check;
@@ -1727,6 +1872,7 @@ int bpf_check(struct bpf_prog *prog, union bpf_attr *attr)
skip_full_check:
while (pop_stack(env, NULL) >= 0);
+ free_states(env);
if (log_level && log_len >= log_size - 1) {
BUG_ON(log_len >= log_size);
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-14 08:20:25 +0000