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-rw-r--r--kernel/bpf/verifier.c143
1 files changed, 131 insertions, 12 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8d3a4ef1d969..25baa3c8cdd2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -721,6 +721,8 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
dst_state->speculative = src->speculative;
dst_state->curframe = src->curframe;
dst_state->active_spin_lock = src->active_spin_lock;
+ dst_state->branches = src->branches;
+ dst_state->parent = src->parent;
for (i = 0; i <= src->curframe; i++) {
dst = dst_state->frame[i];
if (!dst) {
@@ -736,6 +738,23 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
return 0;
}
+static void update_branch_counts(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
+{
+ while (st) {
+ u32 br = --st->branches;
+
+ /* WARN_ON(br > 1) technically makes sense here,
+ * but see comment in push_stack(), hence:
+ */
+ WARN_ONCE((int)br < 0,
+ "BUG update_branch_counts:branches_to_explore=%d\n",
+ br);
+ if (br)
+ break;
+ st = st->parent;
+ }
+}
+
static int pop_stack(struct bpf_verifier_env *env, int *prev_insn_idx,
int *insn_idx)
{
@@ -789,6 +808,18 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
env->stack_size);
goto err;
}
+ if (elem->st.parent) {
+ ++elem->st.parent->branches;
+ /* WARN_ON(branches > 2) technically makes sense here,
+ * but
+ * 1. speculative states will bump 'branches' for non-branch
+ * instructions
+ * 2. is_state_visited() heuristics may decide not to create
+ * a new state for a sequence of branches and all such current
+ * and cloned states will be pointing to a single parent state
+ * which might have large 'branches' count.
+ */
+ }
return &elem->st;
err:
free_verifier_state(env->cur_state, true);
@@ -5682,7 +5713,8 @@ static void init_explored_state(struct bpf_verifier_env *env, int idx)
* w - next instruction
* e - edge
*/
-static int push_insn(int t, int w, int e, struct bpf_verifier_env *env)
+static int push_insn(int t, int w, int e, struct bpf_verifier_env *env,
+ bool loop_ok)
{
int *insn_stack = env->cfg.insn_stack;
int *insn_state = env->cfg.insn_state;
@@ -5712,6 +5744,8 @@ static int push_insn(int t, int w, int e, struct bpf_verifier_env *env)
insn_stack[env->cfg.cur_stack++] = w;
return 1;
} else if ((insn_state[w] & 0xF0) == DISCOVERED) {
+ if (loop_ok && env->allow_ptr_leaks)
+ return 0;
verbose_linfo(env, t, "%d: ", t);
verbose_linfo(env, w, "%d: ", w);
verbose(env, "back-edge from insn %d to %d\n", t, w);
@@ -5763,7 +5797,7 @@ peek_stack:
if (opcode == BPF_EXIT) {
goto mark_explored;
} else if (opcode == BPF_CALL) {
- ret = push_insn(t, t + 1, FALLTHROUGH, env);
+ ret = push_insn(t, t + 1, FALLTHROUGH, env, false);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
@@ -5772,7 +5806,8 @@ peek_stack:
init_explored_state(env, t + 1);
if (insns[t].src_reg == BPF_PSEUDO_CALL) {
init_explored_state(env, t);
- ret = push_insn(t, t + insns[t].imm + 1, BRANCH, env);
+ ret = push_insn(t, t + insns[t].imm + 1, BRANCH,
+ env, false);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
@@ -5785,7 +5820,7 @@ peek_stack:
}
/* unconditional jump with single edge */
ret = push_insn(t, t + insns[t].off + 1,
- FALLTHROUGH, env);
+ FALLTHROUGH, env, true);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
@@ -5798,13 +5833,13 @@ peek_stack:
} else {
/* conditional jump with two edges */
init_explored_state(env, t);
- ret = push_insn(t, t + 1, FALLTHROUGH, env);
+ ret = push_insn(t, t + 1, FALLTHROUGH, env, true);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
goto err_free;
- ret = push_insn(t, t + insns[t].off + 1, BRANCH, env);
+ ret = push_insn(t, t + insns[t].off + 1, BRANCH, env, true);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
@@ -5814,7 +5849,7 @@ peek_stack:
/* all other non-branch instructions with single
* fall-through edge
*/
- ret = push_insn(t, t + 1, FALLTHROUGH, env);
+ ret = push_insn(t, t + 1, FALLTHROUGH, env, false);
if (ret == 1)
goto peek_stack;
else if (ret < 0)
@@ -6247,6 +6282,8 @@ static void clean_live_states(struct bpf_verifier_env *env, int insn,
sl = *explored_state(env, insn);
while (sl) {
+ if (sl->state.branches)
+ goto next;
if (sl->state.insn_idx != insn ||
sl->state.curframe != cur->curframe)
goto next;
@@ -6611,12 +6648,32 @@ static int propagate_liveness(struct bpf_verifier_env *env,
return 0;
}
+static bool states_maybe_looping(struct bpf_verifier_state *old,
+ struct bpf_verifier_state *cur)
+{
+ struct bpf_func_state *fold, *fcur;
+ int i, fr = cur->curframe;
+
+ if (old->curframe != fr)
+ return false;
+
+ fold = old->frame[fr];
+ fcur = cur->frame[fr];
+ for (i = 0; i < MAX_BPF_REG; i++)
+ if (memcmp(&fold->regs[i], &fcur->regs[i],
+ offsetof(struct bpf_reg_state, parent)))
+ return false;
+ return true;
+}
+
+
static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
{
struct bpf_verifier_state_list *new_sl;
struct bpf_verifier_state_list *sl, **pprev;
struct bpf_verifier_state *cur = env->cur_state, *new;
int i, j, err, states_cnt = 0;
+ bool add_new_state = false;
if (!env->insn_aux_data[insn_idx].prune_point)
/* this 'insn_idx' instruction wasn't marked, so we will not
@@ -6624,6 +6681,18 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
*/
return 0;
+ /* bpf progs typically have pruning point every 4 instructions
+ * http://vger.kernel.org/bpfconf2019.html#session-1
+ * Do not add new state for future pruning if the verifier hasn't seen
+ * at least 2 jumps and at least 8 instructions.
+ * This heuristics helps decrease 'total_states' and 'peak_states' metric.
+ * In tests that amounts to up to 50% reduction into total verifier
+ * memory consumption and 20% verifier time speedup.
+ */
+ if (env->jmps_processed - env->prev_jmps_processed >= 2 &&
+ env->insn_processed - env->prev_insn_processed >= 8)
+ add_new_state = true;
+
pprev = explored_state(env, insn_idx);
sl = *pprev;
@@ -6633,6 +6702,30 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
states_cnt++;
if (sl->state.insn_idx != insn_idx)
goto next;
+ if (sl->state.branches) {
+ if (states_maybe_looping(&sl->state, cur) &&
+ states_equal(env, &sl->state, cur)) {
+ verbose_linfo(env, insn_idx, "; ");
+ verbose(env, "infinite loop detected at insn %d\n", insn_idx);
+ return -EINVAL;
+ }
+ /* if the verifier is processing a loop, avoid adding new state
+ * too often, since different loop iterations have distinct
+ * states and may not help future pruning.
+ * This threshold shouldn't be too low to make sure that
+ * a loop with large bound will be rejected quickly.
+ * The most abusive loop will be:
+ * r1 += 1
+ * if r1 < 1000000 goto pc-2
+ * 1M insn_procssed limit / 100 == 10k peak states.
+ * This threshold shouldn't be too high either, since states
+ * at the end of the loop are likely to be useful in pruning.
+ */
+ if (env->jmps_processed - env->prev_jmps_processed < 20 &&
+ env->insn_processed - env->prev_insn_processed < 100)
+ add_new_state = false;
+ goto miss;
+ }
if (states_equal(env, &sl->state, cur)) {
sl->hit_cnt++;
/* reached equivalent register/stack state,
@@ -6650,7 +6743,15 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
return err;
return 1;
}
- sl->miss_cnt++;
+miss:
+ /* when new state is not going to be added do not increase miss count.
+ * Otherwise several loop iterations will remove the state
+ * recorded earlier. The goal of these heuristics is to have
+ * states from some iterations of the loop (some in the beginning
+ * and some at the end) to help pruning.
+ */
+ if (add_new_state)
+ sl->miss_cnt++;
/* heuristic to determine whether this state is beneficial
* to keep checking from state equivalence point of view.
* Higher numbers increase max_states_per_insn and verification time,
@@ -6662,6 +6763,11 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
*/
*pprev = sl->next;
if (sl->state.frame[0]->regs[0].live & REG_LIVE_DONE) {
+ u32 br = sl->state.branches;
+
+ WARN_ONCE(br,
+ "BUG live_done but branches_to_explore %d\n",
+ br);
free_verifier_state(&sl->state, false);
kfree(sl);
env->peak_states--;
@@ -6687,18 +6793,25 @@ next:
if (!env->allow_ptr_leaks && states_cnt > BPF_COMPLEXITY_LIMIT_STATES)
return 0;
- /* there were no equivalent states, remember current one.
- * technically the current state is not proven to be safe yet,
+ if (!add_new_state)
+ return 0;
+
+ /* There were no equivalent states, remember the current one.
+ * Technically the current state is not proven to be safe yet,
* but it will either reach outer most bpf_exit (which means it's safe)
- * or it will be rejected. Since there are no loops, we won't be
+ * or it will be rejected. When there are no loops the verifier won't be
* seeing this tuple (frame[0].callsite, frame[1].callsite, .. insn_idx)
- * again on the way to bpf_exit
+ * again on the way to bpf_exit.
+ * When looping the sl->state.branches will be > 0 and this state
+ * will not be considered for equivalence until branches == 0.
*/
new_sl = kzalloc(sizeof(struct bpf_verifier_state_list), GFP_KERNEL);
if (!new_sl)
return -ENOMEM;
env->total_states++;
env->peak_states++;
+ env->prev_jmps_processed = env->jmps_processed;
+ env->prev_insn_processed = env->insn_processed;
/* add new state to the head of linked list */
new = &new_sl->state;
@@ -6709,6 +6822,9 @@ next:
return err;
}
new->insn_idx = insn_idx;
+ WARN_ONCE(new->branches != 1,
+ "BUG is_state_visited:branches_to_explore=%d insn %d\n", new->branches, insn_idx);
+ cur->parent = new;
new_sl->next = *explored_state(env, insn_idx);
*explored_state(env, insn_idx) = new_sl;
/* connect new state to parentage chain. Current frame needs all
@@ -6795,6 +6911,7 @@ static int do_check(struct bpf_verifier_env *env)
return -ENOMEM;
state->curframe = 0;
state->speculative = false;
+ state->branches = 1;
state->frame[0] = kzalloc(sizeof(struct bpf_func_state), GFP_KERNEL);
if (!state->frame[0]) {
kfree(state);
@@ -7001,6 +7118,7 @@ static int do_check(struct bpf_verifier_env *env)
} else if (class == BPF_JMP || class == BPF_JMP32) {
u8 opcode = BPF_OP(insn->code);
+ env->jmps_processed++;
if (opcode == BPF_CALL) {
if (BPF_SRC(insn->code) != BPF_K ||
insn->off != 0 ||
@@ -7086,6 +7204,7 @@ static int do_check(struct bpf_verifier_env *env)
if (err)
return err;
process_bpf_exit:
+ update_branch_counts(env, env->cur_state);
err = pop_stack(env, &env->prev_insn_idx,
&env->insn_idx);
if (err < 0) {
generated by cgit v1.2.3-58-ga151 (git 2.39.0) at 2024-11-24 05:04:43 +0000