Merge branch 'bpf-copy_verifier_state-should-copy-loop_entry-field'

Eduard Zingerman says: ==================== This patch set fixes a bug in copy_verifier_state() where the loop_entry field was not copied. This omission led to incorrect loop_entry fields remaining in env->cur_state, causing incorrect decisions about loop entry assignments in update_loop_entry(). An example of an unsafe program accepted by the verifier due to this bug can be found in patch #2. This bug can also cause an infinite loop in the verifier, see patch #5. Structure of the patch set: - Patch #1 fixes the bug but has a significant negative impact on verification performance for sched_ext programs. - Patch #3 mitigates the verification performance impact of patch #1 by avoiding clean_live_states() for states whose loop_entry is still being verified. This reduces the number of processed instructions for sched_ext programs by 28–92% in some cases. - Patches #5-6 simplify {get,update}_loop_entry() logic (and are not strictly necessary). - Patches #7–10 mitigate the memory overhead introduced by patch #1 when a program with iterator-based loop hits the 1M instruction limit. This is achieved by freeing states in env->free_list when their branches and used_as_loop_entry counts reach zero. Patches #1-4 were previously sent as a part of [1]. [1] https://lore.kernel.org/bpf/20250122120442.3536298-1-eddyz87@gmail.com/ ==================== Link: https://patch.msgid.link/20250215110411.3236773-1-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2026-04-15 10:42:40 -04:00 · 2025-02-18 19:23:00 -08:00
parent 0fc6025c95 574078b001
commit 654765b5c6
3 changed files with 296 additions and 97 deletions
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -427,11 +427,6 @@ struct bpf_verifier_state {
 	bool active_rcu_lock;

 	bool speculative;
-	/* If this state was ever pointed-to by other state's loop_entry field
-	 * this flag would be set to true. Used to avoid freeing such states
-	 * while they are still in use.
-	 */
-	bool used_as_loop_entry;
 	bool in_sleepable;

 	/* first and last insn idx of this verifier state */
@@ -458,6 +453,11 @@ struct bpf_verifier_state {
 	u32 dfs_depth;
 	u32 callback_unroll_depth;
 	u32 may_goto_depth;
+	/* If this state was ever pointed-to by other state's loop_entry field
+	 * this flag would be set to true. Used to avoid freeing such states
+	 * while they are still in use.
+	 */
+	u32 used_as_loop_entry;
 };

 #define bpf_get_spilled_reg(slot, frame, mask)				\
@@ -498,8 +498,10 @@ struct bpf_verifier_state {
 /* linked list of verifier states used to prune search */
 struct bpf_verifier_state_list {
 	struct bpf_verifier_state state;
-	struct bpf_verifier_state_list *next;
-	int miss_cnt, hit_cnt;
+	struct list_head node;
+	u32 miss_cnt;
+	u32 hit_cnt:31;
+	u32 in_free_list:1;
 };

 struct bpf_loop_inline_state {
@@ -710,8 +712,11 @@ struct bpf_verifier_env {
 	bool test_state_freq;		/* test verifier with different pruning frequency */
 	bool test_reg_invariants;	/* fail verification on register invariants violations */
 	struct bpf_verifier_state *cur_state; /* current verifier state */
-	struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
-	struct bpf_verifier_state_list *free_list;
+	/* Search pruning optimization, array of list_heads for
+	 * lists of struct bpf_verifier_state_list.
+	 */
+	struct list_head *explored_states;
+	struct list_head free_list;	/* list of struct bpf_verifier_state_list */
 	struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
 	struct btf_mod_pair used_btfs[MAX_USED_BTFS]; /* array of BTF's used by BPF program */
 	u32 used_map_cnt;		/* number of used maps */
@@ -767,6 +772,8 @@ struct bpf_verifier_env {
 	u32 peak_states;
 	/* longest register parentage chain walked for liveness marking */
 	u32 longest_mark_read_walk;
+	u32 free_list_size;
+	u32 explored_states_size;
 	bpfptr_t fd_array;

 	/* bit mask to keep track of whether a register has been accessed
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1609,6 +1609,14 @@ static struct bpf_reference_state *find_lock_state(struct bpf_verifier_state *st
 	return NULL;
 }

+static void update_peak_states(struct bpf_verifier_env *env)
+{
+	u32 cur_states;
+
+	cur_states = env->explored_states_size + env->free_list_size;
+	env->peak_states = max(env->peak_states, cur_states);
+}
+
 static void free_func_state(struct bpf_func_state *state)
 {
 	if (!state)
@@ -1631,6 +1639,50 @@ static void free_verifier_state(struct bpf_verifier_state *state,
 		kfree(state);
 }

+/* struct bpf_verifier_state->{parent,loop_entry} refer to states
+ * that are in either of env->{expored_states,free_list}.
+ * In both cases the state is contained in struct bpf_verifier_state_list.
+ */
+static struct bpf_verifier_state_list *state_parent_as_list(struct bpf_verifier_state *st)
+{
+	if (st->parent)
+		return container_of(st->parent, struct bpf_verifier_state_list, state);
+	return NULL;
+}
+
+static struct bpf_verifier_state_list *state_loop_entry_as_list(struct bpf_verifier_state *st)
+{
+	if (st->loop_entry)
+		return container_of(st->loop_entry, struct bpf_verifier_state_list, state);
+	return NULL;
+}
+
+/* A state can be freed if it is no longer referenced:
+ * - is in the env->free_list;
+ * - has no children states;
+ * - is not used as loop_entry.
+ *
+ * Freeing a state can make it's loop_entry free-able.
+ */
+static void maybe_free_verifier_state(struct bpf_verifier_env *env,
+				      struct bpf_verifier_state_list *sl)
+{
+	struct bpf_verifier_state_list *loop_entry_sl;
+
+	while (sl && sl->in_free_list &&
+		     sl->state.branches == 0 &&
+		     sl->state.used_as_loop_entry == 0) {
+		loop_entry_sl = state_loop_entry_as_list(&sl->state);
+		if (loop_entry_sl)
+			loop_entry_sl->state.used_as_loop_entry--;
+		list_del(&sl->node);
+		free_verifier_state(&sl->state, false);
+		kfree(sl);
+		env->free_list_size--;
+		sl = loop_entry_sl;
+	}
+}
+
 /* copy verifier state from src to dst growing dst stack space
 * when necessary to accommodate larger src stack
 */
@@ -1670,6 +1722,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 	dst_state->callback_unroll_depth = src->callback_unroll_depth;
 	dst_state->used_as_loop_entry = src->used_as_loop_entry;
 	dst_state->may_goto_depth = src->may_goto_depth;
+	dst_state->loop_entry = src->loop_entry;
 	for (i = 0; i <= src->curframe; i++) {
 		dst = dst_state->frame[i];
 		if (!dst) {
@@ -1690,7 +1743,7 @@ static u32 state_htab_size(struct bpf_verifier_env *env)
 	return env->prog->len;
 }

-static struct bpf_verifier_state_list **explored_state(struct bpf_verifier_env *env, int idx)
+static struct list_head *explored_state(struct bpf_verifier_env *env, int idx)
 {
 	struct bpf_verifier_state *cur = env->cur_state;
 	struct bpf_func_state *state = cur->frame[cur->curframe];
@@ -1798,16 +1851,13 @@ static bool same_callsites(struct bpf_verifier_state *a, struct bpf_verifier_sta
 *     # Find outermost loop entry known for n
 *     def get_loop_entry(n):
 *         h = entries.get(n, None)
- *         while h in entries and entries[h] != h:
+ *         while h in entries:
 *             h = entries[h]
 *         return h
 *
- *     # Update n's loop entry if h's outermost entry comes
- *     # before n's outermost entry in current DFS path.
+ *     # Update n's loop entry if h comes before n in current DFS path.
 *     def update_loop_entry(n, h):
- *         n1 = get_loop_entry(n) or n
- *         h1 = get_loop_entry(h) or h
- *         if h1 in path and depths[h1] <= depths[n1]:
+ *         if h in path and depths[entries.get(n, n)] < depths[n]:
 *             entries[n] = h1
 *
 *     def dfs(n, depth):
@@ -1819,7 +1869,7 @@ static bool same_callsites(struct bpf_verifier_state *a, struct bpf_verifier_sta
 *                 # Case A: explore succ and update cur's loop entry
 *                 #         only if succ's entry is in current DFS path.
 *                 dfs(succ, depth + 1)
- *                 h = get_loop_entry(succ)
+ *                 h = entries.get(succ, None)
 *                 update_loop_entry(n, h)
 *             else:
 *                 # Case B or C depending on `h1 in path` check in update_loop_entry().
@@ -1831,46 +1881,49 @@ static bool same_callsites(struct bpf_verifier_state *a, struct bpf_verifier_sta
 *   and cur's loop entry has to be updated (case A), handle this in
 *   update_branch_counts();
 * - use st->branch > 0 as a signal that st is in the current DFS path;
- * - handle cases B and C in is_state_visited();
- * - update topmost loop entry for intermediate states in get_loop_entry().
+ * - handle cases B and C in is_state_visited().
 */
-static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_state *st)
+static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_env *env,
+						 struct bpf_verifier_state *st)
 {
-	struct bpf_verifier_state *topmost = st->loop_entry, *old;
+	struct bpf_verifier_state *topmost = st->loop_entry;
+	u32 steps = 0;

-	while (topmost && topmost->loop_entry && topmost != topmost->loop_entry)
+	while (topmost && topmost->loop_entry) {
+		if (steps++ > st->dfs_depth) {
+			WARN_ONCE(true, "verifier bug: infinite loop in get_loop_entry\n");
+			verbose(env, "verifier bug: infinite loop in get_loop_entry()\n");
+			return ERR_PTR(-EFAULT);
+		}
 		topmost = topmost->loop_entry;
-	/* Update loop entries for intermediate states to avoid this
-	 * traversal in future get_loop_entry() calls.
-	 */
-	while (st && st->loop_entry != topmost) {
-		old = st->loop_entry;
-		st->loop_entry = topmost;
-		st = old;
 	}
 	return topmost;
 }

-static void update_loop_entry(struct bpf_verifier_state *cur, struct bpf_verifier_state *hdr)
+static void update_loop_entry(struct bpf_verifier_env *env,
+			      struct bpf_verifier_state *cur, struct bpf_verifier_state *hdr)
 {
-	struct bpf_verifier_state *cur1, *hdr1;
-
-	cur1 = get_loop_entry(cur) ?: cur;
-	hdr1 = get_loop_entry(hdr) ?: hdr;
-	/* The head1->branches check decides between cases B and C in
-	 * comment for get_loop_entry(). If hdr1->branches == 0 then
+	/* The hdr->branches check decides between cases B and C in
+	 * comment for get_loop_entry(). If hdr->branches == 0 then
 	 * head's topmost loop entry is not in current DFS path,
 	 * hence 'cur' and 'hdr' are not in the same loop and there is
 	 * no need to update cur->loop_entry.
 	 */
-	if (hdr1->branches && hdr1->dfs_depth <= cur1->dfs_depth) {
+	if (hdr->branches && hdr->dfs_depth < (cur->loop_entry ?: cur)->dfs_depth) {
+		if (cur->loop_entry) {
+			cur->loop_entry->used_as_loop_entry--;
+			maybe_free_verifier_state(env, state_loop_entry_as_list(cur));
+		}
 		cur->loop_entry = hdr;
-		hdr->used_as_loop_entry = true;
+		hdr->used_as_loop_entry++;
 	}
 }

 static void update_branch_counts(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
 {
+	struct bpf_verifier_state_list *sl = NULL, *parent_sl;
+	struct bpf_verifier_state *parent;
+
 	while (st) {
 		u32 br = --st->branches;

@@ -1880,7 +1933,7 @@ static void update_branch_counts(struct bpf_verifier_env *env, struct bpf_verifi
 		 * This is a part of 'case A' in get_loop_entry() comment.
 		 */
 		if (br == 0 && st->parent && st->loop_entry)
-			update_loop_entry(st->parent, st->loop_entry);
+			update_loop_entry(env, st->parent, st->loop_entry);

 		/* WARN_ON(br > 1) technically makes sense here,
 		 * but see comment in push_stack(), hence:
@@ -1890,7 +1943,12 @@ static void update_branch_counts(struct bpf_verifier_env *env, struct bpf_verifi
 			  br);
 		if (br)
 			break;
-		st = st->parent;
+		parent = st->parent;
+		parent_sl = state_parent_as_list(st);
+		if (sl)
+			maybe_free_verifier_state(env, sl);
+		st = parent;
+		sl = parent_sl;
 	}
 }

@@ -8450,10 +8508,12 @@ static struct bpf_verifier_state *find_prev_entry(struct bpf_verifier_env *env,
 {
 	struct bpf_verifier_state_list *sl;
 	struct bpf_verifier_state *st;
+	struct list_head *pos, *head;

 	/* Explored states are pushed in stack order, most recent states come first */
-	sl = *explored_state(env, insn_idx);
-	for (; sl; sl = sl->next) {
+	head = explored_state(env, insn_idx);
+	list_for_each(pos, head) {
+		sl = container_of(pos, struct bpf_verifier_state_list, node);
 		/* If st->branches != 0 state is a part of current DFS verification path,
 		 * hence cur & st for a loop.
 		 */
@@ -17862,18 +17922,22 @@ static void clean_verifier_state(struct bpf_verifier_env *env,
 static void clean_live_states(struct bpf_verifier_env *env, int insn,
 			      struct bpf_verifier_state *cur)
 {
+	struct bpf_verifier_state *loop_entry;
 	struct bpf_verifier_state_list *sl;
+	struct list_head *pos, *head;

-	sl = *explored_state(env, insn);
-	while (sl) {
+	head = explored_state(env, insn);
+	list_for_each(pos, head) {
+		sl = container_of(pos, struct bpf_verifier_state_list, node);
 		if (sl->state.branches)
-			goto next;
+			continue;
+		loop_entry = get_loop_entry(env, &sl->state);
+		if (!IS_ERR_OR_NULL(loop_entry) && loop_entry->branches)
+			continue;
 		if (sl->state.insn_idx != insn ||
 		    !same_callsites(&sl->state, cur))
-			goto next;
+			continue;
 		clean_verifier_state(env, &sl->state);
-next:
-		sl = sl->next;
 	}
 }

@@ -18564,10 +18628,11 @@ static bool iter_active_depths_differ(struct bpf_verifier_state *old, struct bpf
 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_list *sl;
 	struct bpf_verifier_state *cur = env->cur_state, *new, *loop_entry;
 	int i, j, n, err, states_cnt = 0;
 	bool force_new_state, add_new_state, force_exact;
+	struct list_head *pos, *tmp, *head;

 	force_new_state = env->test_state_freq || is_force_checkpoint(env, insn_idx) ||
 			  /* Avoid accumulating infinitely long jmp history */
@@ -18586,15 +18651,14 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 	    env->insn_processed - env->prev_insn_processed >= 8)
 		add_new_state = true;

-	pprev = explored_state(env, insn_idx);
-	sl = *pprev;
-
 	clean_live_states(env, insn_idx, cur);

-	while (sl) {
+	head = explored_state(env, insn_idx);
+	list_for_each_safe(pos, tmp, head) {
+		sl = container_of(pos, struct bpf_verifier_state_list, node);
 		states_cnt++;
 		if (sl->state.insn_idx != insn_idx)
-			goto next;
+			continue;

 		if (sl->state.branches) {
 			struct bpf_func_state *frame = sl->state.frame[sl->state.curframe];
@@ -18668,7 +18732,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 					spi = __get_spi(iter_reg->off + iter_reg->var_off.value);
 					iter_state = &func(env, iter_reg)->stack[spi].spilled_ptr;
 					if (iter_state->iter.state == BPF_ITER_STATE_ACTIVE) {
-						update_loop_entry(cur, &sl->state);
+						update_loop_entry(env, cur, &sl->state);
 						goto hit;
 					}
 				}
@@ -18677,7 +18741,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			if (is_may_goto_insn_at(env, insn_idx)) {
 				if (sl->state.may_goto_depth != cur->may_goto_depth &&
 				    states_equal(env, &sl->state, cur, RANGE_WITHIN)) {
-					update_loop_entry(cur, &sl->state);
+					update_loop_entry(env, cur, &sl->state);
 					goto hit;
 				}
 			}
@@ -18744,11 +18808,13 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 		 *
 		 * Additional details are in the comment before get_loop_entry().
 		 */
-		loop_entry = get_loop_entry(&sl->state);
+		loop_entry = get_loop_entry(env, &sl->state);
+		if (IS_ERR(loop_entry))
+			return PTR_ERR(loop_entry);
 		force_exact = loop_entry && loop_entry->branches > 0;
 		if (states_equal(env, &sl->state, cur, force_exact ? RANGE_WITHIN : NOT_EXACT)) {
 			if (force_exact)
-				update_loop_entry(cur, loop_entry);
+				update_loop_entry(env, cur, loop_entry);
 hit:
 			sl->hit_cnt++;
 			/* reached equivalent register/stack state,
@@ -18797,31 +18863,13 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			/* the state is unlikely to be useful. Remove it to
 			 * speed up verification
 			 */
-			*pprev = sl->next;
-			if (sl->state.frame[0]->regs[0].live & REG_LIVE_DONE &&
-			    !sl->state.used_as_loop_entry) {
-				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--;
-			} else {
-				/* cannot free this state, since parentage chain may
-				 * walk it later. Add it for free_list instead to
-				 * be freed at the end of verification
-				 */
-				sl->next = env->free_list;
-				env->free_list = sl;
-			}
-			sl = *pprev;
-			continue;
+			sl->in_free_list = true;
+			list_del(&sl->node);
+			list_add(&sl->node, &env->free_list);
+			env->free_list_size++;
+			env->explored_states_size--;
+			maybe_free_verifier_state(env, sl);
 		}
-next:
-		pprev = &sl->next;
-		sl = *pprev;
 	}

 	if (env->max_states_per_insn < states_cnt)
@@ -18846,7 +18894,8 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 	if (!new_sl)
 		return -ENOMEM;
 	env->total_states++;
-	env->peak_states++;
+	env->explored_states_size++;
+	update_peak_states(env);
 	env->prev_jmps_processed = env->jmps_processed;
 	env->prev_insn_processed = env->insn_processed;

@@ -18870,8 +18919,8 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 	cur->first_insn_idx = insn_idx;
 	cur->insn_hist_start = cur->insn_hist_end;
 	cur->dfs_depth = new->dfs_depth + 1;
-	new_sl->next = *explored_state(env, insn_idx);
-	*explored_state(env, insn_idx) = new_sl;
+	list_add(&new_sl->node, head);
+
 	/* connect new state to parentage chain. Current frame needs all
 	 * registers connected. Only r6 - r9 of the callers are alive (pushed
 	 * to the stack implicitly by JITs) so in callers' frames connect just
@@ -19292,6 +19341,8 @@ static int do_check(struct bpf_verifier_env *env)
 						return err;
 					break;
 				} else {
+					if (WARN_ON_ONCE(env->cur_state->loop_entry))
+						env->cur_state->loop_entry = NULL;
 					do_print_state = true;
 					continue;
 				}
@@ -22193,31 +22244,29 @@ static int remove_fastcall_spills_fills(struct bpf_verifier_env *env)

 static void free_states(struct bpf_verifier_env *env)
 {
-	struct bpf_verifier_state_list *sl, *sln;
+	struct bpf_verifier_state_list *sl;
+	struct list_head *head, *pos, *tmp;
 	int i;

-	sl = env->free_list;
-	while (sl) {
-		sln = sl->next;
+	list_for_each_safe(pos, tmp, &env->free_list) {
+		sl = container_of(pos, struct bpf_verifier_state_list, node);
 		free_verifier_state(&sl->state, false);
 		kfree(sl);
-		sl = sln;
 	}
-	env->free_list = NULL;
+	INIT_LIST_HEAD(&env->free_list);

 	if (!env->explored_states)
 		return;

 	for (i = 0; i < state_htab_size(env); i++) {
-		sl = env->explored_states[i];
+		head = &env->explored_states[i];

-		while (sl) {
-			sln = sl->next;
+		list_for_each_safe(pos, tmp, head) {
+			sl = container_of(pos, struct bpf_verifier_state_list, node);
 			free_verifier_state(&sl->state, false);
 			kfree(sl);
-			sl = sln;
 		}
-		env->explored_states[i] = NULL;
+		INIT_LIST_HEAD(&env->explored_states[i]);
 	}
 }

@@ -23185,12 +23234,16 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
 	env->test_reg_invariants = attr->prog_flags & BPF_F_TEST_REG_INVARIANTS;

 	env->explored_states = kvcalloc(state_htab_size(env),
-				       sizeof(struct bpf_verifier_state_list *),
+				       sizeof(struct list_head),
 				       GFP_USER);
 	ret = -ENOMEM;
 	if (!env->explored_states)
 		goto skip_full_check;

+	for (i = 0; i < state_htab_size(env); i++)
+		INIT_LIST_HEAD(&env->explored_states[i]);
+	INIT_LIST_HEAD(&env->free_list);
+
 	ret = check_btf_info_early(env, attr, uattr);
 	if (ret < 0)
 		goto skip_full_check;
--- a/tools/testing/selftests/bpf/progs/iters.c
+++ b/tools/testing/selftests/bpf/progs/iters.c
@@ -7,6 +7,8 @@
 #include "bpf_misc.h"
 #include "bpf_compiler.h"

+#define unlikely(x)	__builtin_expect(!!(x), 0)
+
 static volatile int zero = 0;

 int my_pid;
@@ -1174,6 +1176,122 @@ __naked int loop_state_deps2(void)
 	);
 }

+SEC("?raw_tp")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked int loop_state_deps3(void)
+{
+	/* This is equivalent to a C program below.
+	 *
+	 *   if (random() != 24) {       // assume false branch is placed first
+	 *     i = iter_new();           // fp[-8]
+	 *     while (iter_next(i));
+	 *     iter_destroy(i);
+	 *     return;
+	 *   }
+	 *
+	 *   for (i = 10; i > 0; i--);   // increase dfs_depth for child states
+	 *
+	 *   i = iter_new();             // fp[-8]
+	 *   b = -24;                    // r8
+	 *   for (;;) {                  // checkpoint (L)
+	 *     if (iter_next(i))         // checkpoint (N)
+	 *       break;
+	 *     if (random() == 77) {     // assume false branch is placed first
+	 *       *(u64 *)(r10 + b) = 7;  // this is not safe when b == -25
+	 *       iter_destroy(i);
+	 *       return;
+	 *     }
+	 *     if (random() == 42) {     // assume false branch is placed first
+	 *       b = -25;
+	 *     }
+	 *   }
+	 *   iter_destroy(i);
+	 *
+	 * In case of a buggy verifier first loop might poison
+	 * env->cur_state->loop_entry with a state having 0 branches
+	 * and small dfs_depth. This would trigger NOT_EXACT states
+	 * comparison for some states within second loop.
+	 * Specifically, checkpoint (L) might be problematic if:
+	 * - branch with '*(u64 *)(r10 + b) = 7' is not explored yet;
+	 * - checkpoint (L) is first reached in state {b=-24};
+	 * - traversal is pruned at checkpoint (N) setting checkpoint's (L)
+	 *   branch count to 0, thus making it eligible for use in pruning;
+	 * - checkpoint (L) is next reached in state {b=-25},
+	 *   this would cause NOT_EXACT comparison with a state {b=-24}
+	 *   while 'b' is not marked precise yet.
+	 */
+	asm volatile (
+		"call %[bpf_get_prandom_u32];"
+		"if r0 == 24 goto 2f;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 5;"
+		"call %[bpf_iter_num_new];"
+	"1:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 != 0 goto 1b;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+	"2:"
+		/* loop to increase dfs_depth */
+		"r0 = 10;"
+	"3:"
+		"r0 -= 1;"
+		"if r0 != 0 goto 3b;"
+		/* end of loop */
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r8 = -24;"
+	"main_loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto main_loop_end_%=;"
+		/* first if */
+		"call %[bpf_get_prandom_u32];"
+		"if r0 == 77 goto unsafe_write_%=;"
+		/* second if */
+		"call %[bpf_get_prandom_u32];"
+		"if r0 == 42 goto poison_r8_%=;"
+		/* iterate */
+		"goto main_loop_%=;"
+	"main_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+
+	"unsafe_write_%=:"
+		"r0 = r10;"
+		"r0 += r8;"
+		"r1 = 7;"
+		"*(u64 *)(r0 + 0) = r1;"
+		"goto main_loop_end_%=;"
+
+	"poison_r8_%=:"
+		"r8 = -25;"
+		"goto main_loop_%=;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy)
+		: __clobber_all
+	);
+}
+
 SEC("?raw_tp")
 __success
 __naked int triple_continue(void)
@@ -1512,4 +1630,25 @@ int iter_destroy_bad_arg(const void *ctx)
 	return 0;
 }

+SEC("raw_tp")
+__success
+int clean_live_states(const void *ctx)
+{
+	char buf[1];
+	int i, j, k, l, m, n, o;
+
+	bpf_for(i, 0, 10)
+	bpf_for(j, 0, 10)
+	bpf_for(k, 0, 10)
+	bpf_for(l, 0, 10)
+	bpf_for(m, 0, 10)
+	bpf_for(n, 0, 10)
+	bpf_for(o, 0, 10) {
+		if (unlikely(bpf_get_prandom_u32()))
+			buf[0] = 42;
+		bpf_printk("%s", buf);
+	}
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";