Merge branch 'exact-states-comparison-for-iterator-convergence-checks'

Eduard Zingerman says:

====================
exact states comparison for iterator convergence checks

Iterator convergence logic in is_state_visited() uses state_equals()
for states with branches counter > 0 to check if iterator based loop
converges. This is not fully correct because state_equals() relies on
presence of read and precision marks on registers. These marks are not
guaranteed to be finalized while state has branches.
Commit message for patch #3 describes a program that exhibits such
behavior.

This patch-set aims to fix iterator convergence logic by adding notion
of exact states comparison. Exact comparison does not rely on presence
of read or precision marks and thus is more strict.
As explained in commit message for patch #3 exact comparisons require
addition of speculative register bounds widening. The end result for
BPF verifier users could be summarized as follows:

(!) After this update verifier would reject programs that conjure an
    imprecise value on the first loop iteration and use it as precise
    on the second (for iterator based loops).

I urge people to at least skim over the commit message for patch #3.

Patches are organized as follows:
- patches #1,2: moving/extracting utility functions;
- patch #3: introduces exact mode for states comparison and adds
  widening heuristic;
- patch #4: adds test-cases that demonstrate why the series is
  necessary;
- patch #5: extends patch #3 with a notion of state loop entries,
  these entries have to be tracked to correctly identify that
  different verifier states belong to the same states loop;
- patch #6: adds a test-case that demonstrates a program
  which requires loop entry tracking for correct verification;
- patch #7: just adds a few debug prints.

The following actions are planned as a followup for this patch-set:
- implementation has to be adapted for callbacks handling logic as a
  part of a fix for [1];
- it is necessary to explore ways to improve widening heuristic to
  handle iters_task_vma test w/o need to insert barrier_var() calls;
- explored states eviction logic on cache miss has to be extended
  to either:
  - allow eviction of checkpoint states -or-
  - be sped up in case if there are many active checkpoints associated
    with the same instruction.

The patch-set is a followup for mailing list discussion [1].

Changelog:
- V2 [3] -> V3:
  - correct check for stack spills in widen_imprecise_scalars(),
    added test case progs/iters.c:widen_spill to check the behavior
    (suggested by Andrii);
  - allow eviction of checkpoint states in is_state_visited() to avoid
    pathological verifier performance when iterator based loop does not
    converge (discussion with Alexei).
- V1 [2] -> V2, applied changes suggested by Alexei offlist:
  - __explored_state() function removed;
  - same_callsites() function is now used in clean_live_states();
  - patches #1,2 are added as preparatory code movement;
  - in process_iter_next_call() a safeguard is added to verify that
    cur_st->parent exists and has expected insn index / call sites.

[1] https://lore.kernel.org/bpf/97a90da09404c65c8e810cf83c94ac703705dc0e.camel@gmail.com/
[2] https://lore.kernel.org/bpf/20231021005939.1041-1-eddyz87@gmail.com/
[3] https://lore.kernel.org/bpf/20231022010812.9201-1-eddyz87@gmail.com/
====================

Link: https://lore.kernel.org/r/20231024000917.12153-1-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 1133 insertions, 54 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index e67cd45a85be..24213a99cc79 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -373,10 +373,25 @@ struct bpf_verifier_state {
 	struct bpf_active_lock active_lock;
 	bool speculative;
 	bool active_rcu_lock;
+	/* 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;
 
 	/* first and last insn idx of this verifier state */
 	u32 first_insn_idx;
 	u32 last_insn_idx;
+	/* If this state is a part of states loop this field points to some
+	 * parent of this state such that:
+	 * - it is also a member of the same states loop;
+	 * - DFS states traversal starting from initial state visits loop_entry
+	 *   state before this state.
+	 * Used to compute topmost loop entry for state loops.
+	 * State loops might appear because of open coded iterators logic.
+	 * See get_loop_entry() for more information.
+	 */
+	struct bpf_verifier_state *loop_entry;
 	/* jmp history recorded from first to last.
 	 * backtracking is using it to go from last to first.
 	 * For most states jmp_history_cnt is [0-3].
@@ -384,6 +399,7 @@ struct bpf_verifier_state {
 	 */
 	struct bpf_idx_pair *jmp_history;
 	u32 jmp_history_cnt;
+	u32 dfs_depth;
 };
 
 #define bpf_get_spilled_reg(slot, frame, mask)				\
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e9bc5d4a25a1..98f9d0f35931 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1802,6 +1802,8 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 	dst_state->parent = src->parent;
 	dst_state->first_insn_idx = src->first_insn_idx;
 	dst_state->last_insn_idx = src->last_insn_idx;
+	dst_state->dfs_depth = src->dfs_depth;
+	dst_state->used_as_loop_entry = src->used_as_loop_entry;
 	for (i = 0; i <= src->curframe; i++) {
 		dst = dst_state->frame[i];
 		if (!dst) {
@@ -1817,11 +1819,203 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 	return 0;
 }
 
+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)
+{
+	struct bpf_verifier_state *cur = env->cur_state;
+	struct bpf_func_state *state = cur->frame[cur->curframe];
+
+	return &env->explored_states[(idx ^ state->callsite) % state_htab_size(env)];
+}
+
+static bool same_callsites(struct bpf_verifier_state *a, struct bpf_verifier_state *b)
+{
+	int fr;
+
+	if (a->curframe != b->curframe)
+		return false;
+
+	for (fr = a->curframe; fr >= 0; fr--)
+		if (a->frame[fr]->callsite != b->frame[fr]->callsite)
+			return false;
+
+	return true;
+}
+
+/* Open coded iterators allow back-edges in the state graph in order to
+ * check unbounded loops that iterators.
+ *
+ * In is_state_visited() it is necessary to know if explored states are
+ * part of some loops in order to decide whether non-exact states
+ * comparison could be used:
+ * - non-exact states comparison establishes sub-state relation and uses
+ *   read and precision marks to do so, these marks are propagated from
+ *   children states and thus are not guaranteed to be final in a loop;
+ * - exact states comparison just checks if current and explored states
+ *   are identical (and thus form a back-edge).
+ *
+ * Paper "A New Algorithm for Identifying Loops in Decompilation"
+ * by Tao Wei, Jian Mao, Wei Zou and Yu Chen [1] presents a convenient
+ * algorithm for loop structure detection and gives an overview of
+ * relevant terminology. It also has helpful illustrations.
+ *
+ * [1] https://api.semanticscholar.org/CorpusID:15784067
+ *
+ * We use a similar algorithm but because loop nested structure is
+ * irrelevant for verifier ours is significantly simpler and resembles
+ * strongly connected components algorithm from Sedgewick's textbook.
+ *
+ * Define topmost loop entry as a first node of the loop traversed in a
+ * depth first search starting from initial state. The goal of the loop
+ * tracking algorithm is to associate topmost loop entries with states
+ * derived from these entries.
+ *
+ * For each step in the DFS states traversal algorithm needs to identify
+ * the following situations:
+ *
+ *          initial                     initial                   initial
+ *            |                           |                         |
+ *            V                           V                         V
+ *           ...                         ...           .---------> hdr
+ *            |                           |            |            |
+ *            V                           V            |            V
+ *           cur                     .-> succ          |    .------...
+ *            |                      |    |            |    |       |
+ *            V                      |    V            |    V       V
+ *           succ                    '-- cur           |   ...     ...
+ *                                                     |    |       |
+ *                                                     |    V       V
+ *                                                     |   succ <- cur
+ *                                                     |    |
+ *                                                     |    V
+ *                                                     |   ...
+ *                                                     |    |
+ *                                                     '----'
+ *
+ *  (A) successor state of cur   (B) successor state of cur or it's entry
+ *      not yet traversed            are in current DFS path, thus cur and succ
+ *                                   are members of the same outermost loop
+ *
+ *                      initial                  initial
+ *                        |                        |
+ *                        V                        V
+ *                       ...                      ...
+ *                        |                        |
+ *                        V                        V
+ *                .------...               .------...
+ *                |       |                |       |
+ *                V       V                V       V
+ *           .-> hdr     ...              ...     ...
+ *           |    |       |                |       |
+ *           |    V       V                V       V
+ *           |   succ <- cur              succ <- cur
+ *           |    |                        |
+ *           |    V                        V
+ *           |   ...                      ...
+ *           |    |                        |
+ *           '----'                       exit
+ *
+ * (C) successor state of cur is a part of some loop but this loop
+ *     does not include cur or successor state is not in a loop at all.
+ *
+ * Algorithm could be described as the following python code:
+ *
+ *     traversed = set()   # Set of traversed nodes
+ *     entries = {}        # Mapping from node to loop entry
+ *     depths = {}         # Depth level assigned to graph node
+ *     path = set()        # Current DFS path
+ *
+ *     # 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:
+ *             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.
+ *     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]:
+ *             entries[n] = h1
+ *
+ *     def dfs(n, depth):
+ *         traversed.add(n)
+ *         path.add(n)
+ *         depths[n] = depth
+ *         for succ in G.successors(n):
+ *             if succ not in traversed:
+ *                 # 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)
+ *                 update_loop_entry(n, h)
+ *             else:
+ *                 # Case B or C depending on `h1 in path` check in update_loop_entry().
+ *                 update_loop_entry(n, succ)
+ *         path.remove(n)
+ *
+ * To adapt this algorithm for use with verifier:
+ * - use st->branch == 0 as a signal that DFS of succ had been finished
+ *   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().
+ */
+static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_state *st)
+{
+	struct bpf_verifier_state *topmost = st->loop_entry, *old;
+
+	while (topmost && topmost->loop_entry && topmost != topmost->loop_entry)
+		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)
+{
+	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
+	 * 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) {
+		cur->loop_entry = hdr;
+		hdr->used_as_loop_entry = true;
+	}
+}
+
 static void update_branch_counts(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
 {
 	while (st) {
 		u32 br = --st->branches;
 
+		/* br == 0 signals that DFS exploration for 'st' is finished,
+		 * thus it is necessary to update parent's loop entry if it
+		 * turned out that st is a part of some loop.
+		 * 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);
+
 		/* WARN_ON(br > 1) technically makes sense here,
 		 * but see comment in push_stack(), hence:
 		 */
@@ -7696,6 +7890,81 @@ static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
 	return 0;
 }
 
+/* Look for a previous loop entry at insn_idx: nearest parent state
+ * stopped at insn_idx with callsites matching those in cur->frame.
+ */
+static struct bpf_verifier_state *find_prev_entry(struct bpf_verifier_env *env,
+						  struct bpf_verifier_state *cur,
+						  int insn_idx)
+{
+	struct bpf_verifier_state_list *sl;
+	struct bpf_verifier_state *st;
+
+	/* Explored states are pushed in stack order, most recent states come first */
+	sl = *explored_state(env, insn_idx);
+	for (; sl; sl = sl->next) {
+		/* If st->branches != 0 state is a part of current DFS verification path,
+		 * hence cur & st for a loop.
+		 */
+		st = &sl->state;
+		if (st->insn_idx == insn_idx && st->branches && same_callsites(st, cur) &&
+		    st->dfs_depth < cur->dfs_depth)
+			return st;
+	}
+
+	return NULL;
+}
+
+static void reset_idmap_scratch(struct bpf_verifier_env *env);
+static bool regs_exact(const struct bpf_reg_state *rold,
+		       const struct bpf_reg_state *rcur,
+		       struct bpf_idmap *idmap);
+
+static void maybe_widen_reg(struct bpf_verifier_env *env,
+			    struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
+			    struct bpf_idmap *idmap)
+{
+	if (rold->type != SCALAR_VALUE)
+		return;
+	if (rold->type != rcur->type)
+		return;
+	if (rold->precise || rcur->precise || regs_exact(rold, rcur, idmap))
+		return;
+	__mark_reg_unknown(env, rcur);
+}
+
+static int widen_imprecise_scalars(struct bpf_verifier_env *env,
+				   struct bpf_verifier_state *old,
+				   struct bpf_verifier_state *cur)
+{
+	struct bpf_func_state *fold, *fcur;
+	int i, fr;
+
+	reset_idmap_scratch(env);
+	for (fr = old->curframe; fr >= 0; fr--) {
+		fold = old->frame[fr];
+		fcur = cur->frame[fr];
+
+		for (i = 0; i < MAX_BPF_REG; i++)
+			maybe_widen_reg(env,
+					&fold->regs[i],
+					&fcur->regs[i],
+					&env->idmap_scratch);
+
+		for (i = 0; i < fold->allocated_stack / BPF_REG_SIZE; i++) {
+			if (!is_spilled_reg(&fold->stack[i]) ||
+			    !is_spilled_reg(&fcur->stack[i]))
+				continue;
+
+			maybe_widen_reg(env,
+					&fold->stack[i].spilled_ptr,
+					&fcur->stack[i].spilled_ptr,
+					&env->idmap_scratch);
+		}
+	}
+	return 0;
+}
+
 /* process_iter_next_call() is called when verifier gets to iterator's next
  * "method" (e.g., bpf_iter_num_next() for numbers iterator) call. We'll refer
  * to it as just "iter_next()" in comments below.
@@ -7737,25 +8006,47 @@ static int process_iter_arg(struct bpf_verifier_env *env, int regno, int insn_id
  * is some statically known limit on number of iterations (e.g., if there is
  * an explicit `if n > 100 then break;` statement somewhere in the loop).
  *
- * One very subtle but very important aspect is that we *always* simulate NULL
- * condition first (as the current state) before we simulate non-NULL case.
- * This has to do with intricacies of scalar precision tracking. By simulating
- * "exit condition" of iter_next() returning NULL first, we make sure all the
- * relevant precision marks *that will be set **after** we exit iterator loop*
- * are propagated backwards to common parent state of NULL and non-NULL
- * branches. Thanks to that, state equivalence checks done later in forked
- * state, when reaching iter_next() for ACTIVE iterator, can assume that
- * precision marks are finalized and won't change. Because simulating another
- * ACTIVE iterator iteration won't change them (because given same input
- * states we'll end up with exactly same output states which we are currently
- * comparing; and verification after the loop already propagated back what
- * needs to be **additionally** tracked as precise). It's subtle, grok
- * precision tracking for more intuitive understanding.
+ * Iteration convergence logic in is_state_visited() relies on exact
+ * states comparison, which ignores read and precision marks.
+ * This is necessary because read and precision marks are not finalized
+ * while in the loop. Exact comparison might preclude convergence for
+ * simple programs like below:
+ *
+ *     i = 0;
+ *     while(iter_next(&it))
+ *       i++;
+ *
+ * At each iteration step i++ would produce a new distinct state and
+ * eventually instruction processing limit would be reached.
+ *
+ * To avoid such behavior speculatively forget (widen) range for
+ * imprecise scalar registers, if those registers were not precise at the
+ * end of the previous iteration and do not match exactly.
+ *
+ * This is a conservative heuristic that allows to verify wide range of programs,
+ * however it precludes verification of programs that conjure an
+ * imprecise value on the first loop iteration and use it as precise on a second.
+ * For example, the following safe program would fail to verify:
+ *
+ *     struct bpf_num_iter it;
+ *     int arr[10];
+ *     int i = 0, a = 0;
+ *     bpf_iter_num_new(&it, 0, 10);
+ *     while (bpf_iter_num_next(&it)) {
+ *       if (a == 0) {
+ *         a = 1;
+ *         i = 7; // Because i changed verifier would forget
+ *                // it's range on second loop entry.
+ *       } else {
+ *         arr[i] = 42; // This would fail to verify.
+ *       }
+ *     }
+ *     bpf_iter_num_destroy(&it);
  */
 static int process_iter_next_call(struct bpf_verifier_env *env, int insn_idx,
 				  struct bpf_kfunc_call_arg_meta *meta)
 {
-	struct bpf_verifier_state *cur_st = env->cur_state, *queued_st;
+	struct bpf_verifier_state *cur_st = env->cur_state, *queued_st, *prev_st;
 	struct bpf_func_state *cur_fr = cur_st->frame[cur_st->curframe], *queued_fr;
 	struct bpf_reg_state *cur_iter, *queued_iter;
 	int iter_frameno = meta->iter.frameno;
@@ -7773,6 +8064,19 @@ static int process_iter_next_call(struct bpf_verifier_env *env, int insn_idx,
 	}
 
 	if (cur_iter->iter.state == BPF_ITER_STATE_ACTIVE) {
+		/* Because iter_next() call is a checkpoint is_state_visitied()
+		 * should guarantee parent state with same call sites and insn_idx.
+		 */
+		if (!cur_st->parent || cur_st->parent->insn_idx != insn_idx ||
+		    !same_callsites(cur_st->parent, cur_st)) {
+			verbose(env, "bug: bad parent state for iter next call");
+			return -EFAULT;
+		}
+		/* Note cur_st->parent in the call below, it is necessary to skip
+		 * checkpoint created for cur_st by is_state_visited()
+		 * right at this instruction.
+		 */
+		prev_st = find_prev_entry(env, cur_st->parent, insn_idx);
 		/* branch out active iter state */
 		queued_st = push_stack(env, insn_idx + 1, insn_idx, false);
 		if (!queued_st)
@@ -7781,6 +8085,8 @@ static int process_iter_next_call(struct bpf_verifier_env *env, int insn_idx,
 		queued_iter = &queued_st->frame[iter_frameno]->stack[iter_spi].spilled_ptr;
 		queued_iter->iter.state = BPF_ITER_STATE_ACTIVE;
 		queued_iter->iter.depth++;
+		if (prev_st)
+			widen_imprecise_scalars(env, prev_st, queued_st);
 
 		queued_fr = queued_st->frame[queued_st->curframe];
 		mark_ptr_not_null_reg(&queued_fr->regs[BPF_REG_0]);
@@ -15020,21 +15326,6 @@ enum {
 	BRANCH = 2,
 };
 
-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)
-{
-	struct bpf_verifier_state *cur = env->cur_state;
-	struct bpf_func_state *state = cur->frame[cur->curframe];
-
-	return &env->explored_states[(idx ^ state->callsite) % state_htab_size(env)];
-}
-
 static void mark_prune_point(struct bpf_verifier_env *env, int idx)
 {
 	env->insn_aux_data[idx].prune_point = true;
@@ -15911,18 +16202,14 @@ static void clean_live_states(struct bpf_verifier_env *env, int insn,
 			      struct bpf_verifier_state *cur)
 {
 	struct bpf_verifier_state_list *sl;
-	int i;
 
 	sl = *explored_state(env, insn);
 	while (sl) {
 		if (sl->state.branches)
 			goto next;
 		if (sl->state.insn_idx != insn ||
-		    sl->state.curframe != cur->curframe)
+		    !same_callsites(&sl->state, cur))
 			goto next;
-		for (i = 0; i <= cur->curframe; i++)
-			if (sl->state.frame[i]->callsite != cur->frame[i]->callsite)
-				goto next;
 		clean_verifier_state(env, &sl->state);
 next:
 		sl = sl->next;
@@ -15940,8 +16227,11 @@ static bool regs_exact(const struct bpf_reg_state *rold,
 
 /* Returns true if (rold safe implies rcur safe) */
 static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
-		    struct bpf_reg_state *rcur, struct bpf_idmap *idmap)
+		    struct bpf_reg_state *rcur, struct bpf_idmap *idmap, bool exact)
 {
+	if (exact)
+		return regs_exact(rold, rcur, idmap);
+
 	if (!(rold->live & REG_LIVE_READ))
 		/* explored state didn't use this */
 		return true;
@@ -16058,7 +16348,7 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 }
 
 static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
-		      struct bpf_func_state *cur, struct bpf_idmap *idmap)
+		      struct bpf_func_state *cur, struct bpf_idmap *idmap, bool exact)
 {
 	int i, spi;
 
@@ -16071,7 +16361,12 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
 
 		spi = i / BPF_REG_SIZE;
 
-		if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ)) {
+		if (exact &&
+		    old->stack[spi].slot_type[i % BPF_REG_SIZE] !=
+		    cur->stack[spi].slot_type[i % BPF_REG_SIZE])
+			return false;
+
+		if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ) && !exact) {
 			i += BPF_REG_SIZE - 1;
 			/* explored state didn't use this */
 			continue;
@@ -16121,7 +16416,7 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
 			 * return false to continue verification of this path
 			 */
 			if (!regsafe(env, &old->stack[spi].spilled_ptr,
-				     &cur->stack[spi].spilled_ptr, idmap))
+				     &cur->stack[spi].spilled_ptr, idmap, exact))
 				return false;
 			break;
 		case STACK_DYNPTR:
@@ -16203,16 +16498,16 @@ static bool refsafe(struct bpf_func_state *old, struct bpf_func_state *cur,
  * the current state will reach 'bpf_exit' instruction safely
  */
 static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_state *old,
-			      struct bpf_func_state *cur)
+			      struct bpf_func_state *cur, bool exact)
 {
 	int i;
 
 	for (i = 0; i < MAX_BPF_REG; i++)
 		if (!regsafe(env, &old->regs[i], &cur->regs[i],
-			     &env->idmap_scratch))
+			     &env->idmap_scratch, exact))
 			return false;
 
-	if (!stacksafe(env, old, cur, &env->idmap_scratch))
+	if (!stacksafe(env, old, cur, &env->idmap_scratch, exact))
 		return false;
 
 	if (!refsafe(old, cur, &env->idmap_scratch))
@@ -16221,17 +16516,23 @@ static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_stat
 	return true;
 }
 
+static void reset_idmap_scratch(struct bpf_verifier_env *env)
+{
+	env->idmap_scratch.tmp_id_gen = env->id_gen;
+	memset(&env->idmap_scratch.map, 0, sizeof(env->idmap_scratch.map));
+}
+
 static bool states_equal(struct bpf_verifier_env *env,
 			 struct bpf_verifier_state *old,
-			 struct bpf_verifier_state *cur)
+			 struct bpf_verifier_state *cur,
+			 bool exact)
 {
 	int i;
 
 	if (old->curframe != cur->curframe)
 		return false;
 
-	env->idmap_scratch.tmp_id_gen = env->id_gen;
-	memset(&env->idmap_scratch.map, 0, sizeof(env->idmap_scratch.map));
+	reset_idmap_scratch(env);
 
 	/* Verification state from speculative execution simulation
 	 * must never prune a non-speculative execution one.
@@ -16261,7 +16562,7 @@ static bool states_equal(struct bpf_verifier_env *env,
 	for (i = 0; i <= old->curframe; i++) {
 		if (old->frame[i]->callsite != cur->frame[i]->callsite)
 			return false;
-		if (!func_states_equal(env, old->frame[i], cur->frame[i]))
+		if (!func_states_equal(env, old->frame[i], cur->frame[i], exact))
 			return false;
 	}
 	return true;
@@ -16515,10 +16816,11 @@ 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;
+	struct bpf_verifier_state *cur = env->cur_state, *new, *loop_entry;
+	int i, j, n, err, states_cnt = 0;
 	bool force_new_state = env->test_state_freq || is_force_checkpoint(env, insn_idx);
 	bool add_new_state = force_new_state;
+	bool force_exact;
 
 	/* bpf progs typically have pruning point every 4 instructions
 	 * http://vger.kernel.org/bpfconf2019.html#session-1
@@ -16571,9 +16873,33 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			 * It's safe to assume that iterator loop will finish, taking into
 			 * account iter_next() contract of eventually returning
 			 * sticky NULL result.
+			 *
+			 * Note, that states have to be compared exactly in this case because
+			 * read and precision marks might not be finalized inside the loop.
+			 * E.g. as in the program below:
+			 *
+			 *     1. r7 = -16
+			 *     2. r6 = bpf_get_prandom_u32()
+			 *     3. while (bpf_iter_num_next(&fp[-8])) {
+			 *     4.   if (r6 != 42) {
+			 *     5.     r7 = -32
+			 *     6.     r6 = bpf_get_prandom_u32()
+			 *     7.     continue
+			 *     8.   }
+			 *     9.   r0 = r10
+			 *    10.   r0 += r7
+			 *    11.   r8 = *(u64 *)(r0 + 0)
+			 *    12.   r6 = bpf_get_prandom_u32()
+			 *    13. }
+			 *
+			 * Here verifier would first visit path 1-3, create a checkpoint at 3
+			 * with r7=-16, continue to 4-7,3. Existing checkpoint at 3 does
+			 * not have read or precision mark for r7 yet, thus inexact states
+			 * comparison would discard current state with r7=-32
+			 * => unsafe memory access at 11 would not be caught.
 			 */
 			if (is_iter_next_insn(env, insn_idx)) {
-				if (states_equal(env, &sl->state, cur)) {
+				if (states_equal(env, &sl->state, cur, true)) {
 					struct bpf_func_state *cur_frame;
 					struct bpf_reg_state *iter_state, *iter_reg;
 					int spi;
@@ -16589,17 +16915,23 @@ 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)
+					if (iter_state->iter.state == BPF_ITER_STATE_ACTIVE) {
+						update_loop_entry(cur, &sl->state);
 						goto hit;
+					}
 				}
 				goto skip_inf_loop_check;
 			}
 			/* attempt to detect infinite loop to avoid unnecessary doomed work */
 			if (states_maybe_looping(&sl->state, cur) &&
-			    states_equal(env, &sl->state, cur) &&
+			    states_equal(env, &sl->state, cur, false) &&
 			    !iter_active_depths_differ(&sl->state, cur)) {
 				verbose_linfo(env, insn_idx, "; ");
 				verbose(env, "infinite loop detected at insn %d\n", insn_idx);
+				verbose(env, "cur state:");
+				print_verifier_state(env, cur->frame[cur->curframe], true);
+				verbose(env, "old state:");
+				print_verifier_state(env, sl->state.frame[cur->curframe], true);
 				return -EINVAL;
 			}
 			/* if the verifier is processing a loop, avoid adding new state
@@ -16621,7 +16953,36 @@ skip_inf_loop_check:
 				add_new_state = false;
 			goto miss;
 		}
-		if (states_equal(env, &sl->state, cur)) {
+		/* If sl->state is a part of a loop and this loop's entry is a part of
+		 * current verification path then states have to be compared exactly.
+		 * 'force_exact' is needed to catch the following case:
+		 *
+		 *                initial     Here state 'succ' was processed first,
+		 *                  |         it was eventually tracked to produce a
+		 *                  V         state identical to 'hdr'.
+		 *     .---------> hdr        All branches from 'succ' had been explored
+		 *     |            |         and thus 'succ' has its .branches == 0.
+		 *     |            V
+		 *     |    .------...        Suppose states 'cur' and 'succ' correspond
+		 *     |    |       |         to the same instruction + callsites.
+		 *     |    V       V         In such case it is necessary to check
+		 *     |   ...     ...        if 'succ' and 'cur' are states_equal().
+		 *     |    |       |         If 'succ' and 'cur' are a part of the
+		 *     |    V       V         same loop exact flag has to be set.
+		 *     |   succ <- cur        To check if that is the case, verify
+		 *     |    |                 if loop entry of 'succ' is in current
+		 *     |    V                 DFS path.
+		 *     |   ...
+		 *     |    |
+		 *     '----'
+		 *
+		 * Additional details are in the comment before get_loop_entry().
+		 */
+		loop_entry = get_loop_entry(&sl->state);
+		force_exact = loop_entry && loop_entry->branches > 0;
+		if (states_equal(env, &sl->state, cur, force_exact)) {
+			if (force_exact)
+				update_loop_entry(cur, loop_entry);
 hit:
 			sl->hit_cnt++;
 			/* reached equivalent register/stack state,
@@ -16660,13 +17021,18 @@ miss:
 		 * to keep checking from state equivalence point of view.
 		 * Higher numbers increase max_states_per_insn and verification time,
 		 * but do not meaningfully decrease insn_processed.
+		 * 'n' controls how many times state could miss before eviction.
+		 * Use bigger 'n' for checkpoints because evicting checkpoint states
+		 * too early would hinder iterator convergence.
 		 */
-		if (sl->miss_cnt > sl->hit_cnt * 3 + 3) {
+		n = is_force_checkpoint(env, insn_idx) && sl->state.branches > 0 ? 64 : 3;
+		if (sl->miss_cnt > sl->hit_cnt * n + n) {
 			/* 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) {
+			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,
@@ -16735,6 +17101,7 @@ next:
 
 	cur->parent = new;
 	cur->first_insn_idx = insn_idx;
+	cur->dfs_depth = new->dfs_depth + 1;
 	clear_jmp_history(cur);
 	new_sl->next = *explored_state(env, insn_idx);
 	*explored_state(env, insn_idx) = new_sl;
diff --git a/tools/testing/selftests/bpf/progs/iters.c b/tools/testing/selftests/bpf/progs/iters.c
index 6b9b3c56f009..c20c4e38b71c 100644
--- a/tools/testing/selftests/bpf/progs/iters.c
+++ b/tools/testing/selftests/bpf/progs/iters.c
@@ -14,6 +14,13 @@ int my_pid;
 int arr[256];
 int small_arr[16] SEC(".data.small_arr");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 10);
+	__type(key, int);
+	__type(value, int);
+} amap SEC(".maps");
+
 #ifdef REAL_TEST
 #define MY_PID_GUARD() if (my_pid != (bpf_get_current_pid_tgid() >> 32)) return 0
 #else
@@ -716,4 +723,692 @@ int iter_pass_iter_ptr_to_subprog(const void *ctx)
 	return 0;
 }
 
+SEC("?raw_tp")
+__failure
+__msg("R1 type=scalar expected=fp")
+__naked int delayed_read_mark(void)
+{
+	/* This is equivalent to C program below.
+	 * The call to bpf_iter_num_next() is reachable with r7 values &fp[-16] and 0xdead.
+	 * State with r7=&fp[-16] is visited first and follows r6 != 42 ... continue branch.
+	 * At this point iterator next() call is reached with r7 that has no read mark.
+	 * Loop body with r7=0xdead would only be visited if verifier would decide to continue
+	 * with second loop iteration. Absence of read mark on r7 might affect state
+	 * equivalent logic used for iterator convergence tracking.
+	 *
+	 * r7 = &fp[-16]
+	 * fp[-16] = 0
+	 * r6 = bpf_get_prandom_u32()
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   r6++
+	 *   if (r6 != 42) {
+	 *     r7 = 0xdead
+	 *     continue;
+	 *   }
+	 *   bpf_probe_read_user(r7, 8, 0xdeadbeef); // this is not safe
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return 0
+	 */
+	asm volatile (
+		"r7 = r10;"
+		"r7 += -16;"
+		"r0 = 0;"
+		"*(u64 *)(r7 + 0) = r0;"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"1:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto 2f;"
+		"r6 += 1;"
+		"if r6 != 42 goto 3f;"
+		"r7 = 0xdead;"
+		"goto 1b;"
+	"3:"
+		"r1 = r7;"
+		"r2 = 8;"
+		"r3 = 0xdeadbeef;"
+		"call %[bpf_probe_read_user];"
+		"goto 1b;"
+	"2:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy),
+		  __imm(bpf_probe_read_user)
+		: __clobber_all
+	);
+}
+
+SEC("?raw_tp")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__naked int delayed_precision_mark(void)
+{
+	/* This is equivalent to C program below.
+	 * The test is similar to delayed_iter_mark but verifies that incomplete
+	 * precision don't fool verifier.
+	 * The call to bpf_iter_num_next() is reachable with r7 values -16 and -32.
+	 * State with r7=-16 is visited first and follows r6 != 42 ... continue branch.
+	 * At this point iterator next() call is reached with r7 that has no read
+	 * and precision marks.
+	 * Loop body with r7=-32 would only be visited if verifier would decide to continue
+	 * with second loop iteration. Absence of precision mark on r7 might affect state
+	 * equivalent logic used for iterator convergence tracking.
+	 *
+	 * r8 = 0
+	 * fp[-16] = 0
+	 * r7 = -16
+	 * r6 = bpf_get_prandom_u32()
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   if (r6 != 42) {
+	 *     r7 = -32
+	 *     r6 = bpf_get_prandom_u32()
+	 *     continue;
+	 *   }
+	 *   r0 = r10
+	 *   r0 += r7
+	 *   r8 = *(u64 *)(r0 + 0)           // this is not safe
+	 *   r6 = bpf_get_prandom_u32()
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return r8
+	 */
+	asm volatile (
+		"r8 = 0;"
+		"*(u64 *)(r10 - 16) = r8;"
+		"r7 = -16;"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"1:"
+		"r1 = r10;"
+		"r1 += -8;\n"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto 2f;"
+		"if r6 != 42 goto 3f;"
+		"r7 = -32;"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"goto 1b;\n"
+	"3:"
+		"r0 = r10;"
+		"r0 += r7;"
+		"r8 = *(u64 *)(r0 + 0);"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"goto 1b;\n"
+	"2:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = r8;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy),
+		  __imm(bpf_probe_read_user)
+		: __clobber_all
+	);
+}
+
+SEC("?raw_tp")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked int loop_state_deps1(void)
+{
+	/* This is equivalent to C program below.
+	 *
+	 * The case turns out to be tricky in a sense that:
+	 * - states with c=-25 are explored only on a second iteration
+	 *   of the outer loop;
+	 * - states with read+precise mark on c are explored only on
+	 *   second iteration of the inner loop and in a state which
+	 *   is pushed to states stack first.
+	 *
+	 * Depending on the details of iterator convergence logic
+	 * verifier might stop states traversal too early and miss
+	 * unsafe c=-25 memory access.
+	 *
+	 *   j = iter_new();		 // fp[-16]
+	 *   a = 0;			 // r6
+	 *   b = 0;			 // r7
+	 *   c = -24;			 // r8
+	 *   while (iter_next(j)) {
+	 *     i = iter_new();		 // fp[-8]
+	 *     a = 0;			 // r6
+	 *     b = 0;			 // r7
+	 *     while (iter_next(i)) {
+	 *	 if (a == 1) {
+	 *	   a = 0;
+	 *	   b = 1;
+	 *	 } else if (a == 0) {
+	 *	   a = 1;
+	 *	   if (random() == 42)
+	 *	     continue;
+	 *	   if (b == 1) {
+	 *	     *(r10 + c) = 7;  // this is not safe
+	 *	     iter_destroy(i);
+	 *	     iter_destroy(j);
+	 *	     return;
+	 *	   }
+	 *	 }
+	 *     }
+	 *     iter_destroy(i);
+	 *     a = 0;
+	 *     b = 0;
+	 *     c = -25;
+	 *   }
+	 *   iter_destroy(j);
+	 *   return;
+	 */
+	asm volatile (
+		"r1 = r10;"
+		"r1 += -16;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+		"r8 = -24;"
+	"j_loop_%=:"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto j_loop_end_%=;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+	"i_loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto i_loop_end_%=;"
+	"check_one_r6_%=:"
+		"if r6 != 1 goto check_zero_r6_%=;"
+		"r6 = 0;"
+		"r7 = 1;"
+		"goto i_loop_%=;"
+	"check_zero_r6_%=:"
+		"if r6 != 0 goto i_loop_%=;"
+		"r6 = 1;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto check_one_r7_%=;"
+		"goto i_loop_%=;"
+	"check_one_r7_%=:"
+		"if r7 != 1 goto i_loop_%=;"
+		"r0 = r10;"
+		"r0 += r8;"
+		"r1 = 7;"
+		"*(u64 *)(r0 + 0) = r1;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+	"i_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r6 = 0;"
+		"r7 = 0;"
+		"r8 = -25;"
+		"goto j_loop_%=;"
+	"j_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __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")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked int loop_state_deps2(void)
+{
+	/* This is equivalent to C program below.
+	 *
+	 * The case turns out to be tricky in a sense that:
+	 * - states with read+precise mark on c are explored only on a second
+	 *   iteration of the first inner loop and in a state which is pushed to
+	 *   states stack first.
+	 * - states with c=-25 are explored only on a second iteration of the
+	 *   second inner loop and in a state which is pushed to states stack
+	 *   first.
+	 *
+	 * Depending on the details of iterator convergence logic
+	 * verifier might stop states traversal too early and miss
+	 * unsafe c=-25 memory access.
+	 *
+	 *   j = iter_new();             // fp[-16]
+	 *   a = 0;                      // r6
+	 *   b = 0;                      // r7
+	 *   c = -24;                    // r8
+	 *   while (iter_next(j)) {
+	 *     i = iter_new();           // fp[-8]
+	 *     a = 0;                    // r6
+	 *     b = 0;                    // r7
+	 *     while (iter_next(i)) {
+	 *       if (a == 1) {
+	 *         a = 0;
+	 *         b = 1;
+	 *       } else if (a == 0) {
+	 *         a = 1;
+	 *         if (random() == 42)
+	 *           continue;
+	 *         if (b == 1) {
+	 *           *(r10 + c) = 7;     // this is not safe
+	 *           iter_destroy(i);
+	 *           iter_destroy(j);
+	 *           return;
+	 *         }
+	 *       }
+	 *     }
+	 *     iter_destroy(i);
+	 *     i = iter_new();           // fp[-8]
+	 *     a = 0;                    // r6
+	 *     b = 0;                    // r7
+	 *     while (iter_next(i)) {
+	 *       if (a == 1) {
+	 *         a = 0;
+	 *         b = 1;
+	 *       } else if (a == 0) {
+	 *         a = 1;
+	 *         if (random() == 42)
+	 *           continue;
+	 *         if (b == 1) {
+	 *           a = 0;
+	 *           c = -25;
+	 *         }
+	 *       }
+	 *     }
+	 *     iter_destroy(i);
+	 *   }
+	 *   iter_destroy(j);
+	 *   return;
+	 */
+	asm volatile (
+		"r1 = r10;"
+		"r1 += -16;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+		"r8 = -24;"
+	"j_loop_%=:"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto j_loop_end_%=;"
+
+		/* first inner loop */
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+	"i_loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto i_loop_end_%=;"
+	"check_one_r6_%=:"
+		"if r6 != 1 goto check_zero_r6_%=;"
+		"r6 = 0;"
+		"r7 = 1;"
+		"goto i_loop_%=;"
+	"check_zero_r6_%=:"
+		"if r6 != 0 goto i_loop_%=;"
+		"r6 = 1;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto check_one_r7_%=;"
+		"goto i_loop_%=;"
+	"check_one_r7_%=:"
+		"if r7 != 1 goto i_loop_%=;"
+		"r0 = r10;"
+		"r0 += r8;"
+		"r1 = 7;"
+		"*(u64 *)(r0 + 0) = r1;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+	"i_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+
+		/* second inner loop */
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+	"i2_loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto i2_loop_end_%=;"
+	"check2_one_r6_%=:"
+		"if r6 != 1 goto check2_zero_r6_%=;"
+		"r6 = 0;"
+		"r7 = 1;"
+		"goto i2_loop_%=;"
+	"check2_zero_r6_%=:"
+		"if r6 != 0 goto i2_loop_%=;"
+		"r6 = 1;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto check2_one_r7_%=;"
+		"goto i2_loop_%=;"
+	"check2_one_r7_%=:"
+		"if r7 != 1 goto i2_loop_%=;"
+		"r6 = 0;"
+		"r8 = -25;"
+		"goto i2_loop_%=;"
+	"i2_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+
+		"r6 = 0;"
+		"r7 = 0;"
+		"goto j_loop_%=;"
+	"j_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __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)
+{
+	/* This is equivalent to C program below.
+	 * High branching factor of the loop body turned out to be
+	 * problematic for one of the iterator convergence tracking
+	 * algorithms explored.
+	 *
+	 * r6 = bpf_get_prandom_u32()
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   if (bpf_get_prandom_u32() != 42)
+	 *     continue;
+	 *   if (bpf_get_prandom_u32() != 42)
+	 *     continue;
+	 *   if (bpf_get_prandom_u32() != 42)
+	 *     continue;
+	 *   r0 += 0;
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return 0
+	 */
+	asm volatile (
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto loop_end_%=;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto loop_%=;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto loop_%=;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto loop_%=;"
+		"r0 += 0;"
+		"goto loop_%=;"
+	"loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __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 widen_spill(void)
+{
+	/* This is equivalent to C program below.
+	 * The counter is stored in fp[-16], if this counter is not widened
+	 * verifier states representing loop iterations would never converge.
+	 *
+	 * fp[-16] = 0
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   r0 = fp[-16];
+	 *   r0 += 1;
+	 *   fp[-16] = r0;
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return 0
+	 */
+	asm volatile (
+		"r0 = 0;"
+		"*(u64 *)(r10 - 16) = r0;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto loop_end_%=;"
+		"r0 = *(u64 *)(r10 - 16);"
+		"r0 += 1;"
+		"*(u64 *)(r10 - 16) = r0;"
+		"goto loop_%=;"
+	"loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy)
+		: __clobber_all
+	);
+}
+
+SEC("raw_tp")
+__success
+__naked int checkpoint_states_deletion(void)
+{
+	/* This is equivalent to C program below.
+	 *
+	 *   int *a, *b, *c, *d, *e, *f;
+	 *   int i, sum = 0;
+	 *   bpf_for(i, 0, 10) {
+	 *     a = bpf_map_lookup_elem(&amap, &i);
+	 *     b = bpf_map_lookup_elem(&amap, &i);
+	 *     c = bpf_map_lookup_elem(&amap, &i);
+	 *     d = bpf_map_lookup_elem(&amap, &i);
+	 *     e = bpf_map_lookup_elem(&amap, &i);
+	 *     f = bpf_map_lookup_elem(&amap, &i);
+	 *     if (a) sum += 1;
+	 *     if (b) sum += 1;
+	 *     if (c) sum += 1;
+	 *     if (d) sum += 1;
+	 *     if (e) sum += 1;
+	 *     if (f) sum += 1;
+	 *   }
+	 *   return 0;
+	 *
+	 * The body of the loop spawns multiple simulation paths
+	 * with different combination of NULL/non-NULL information for a/b/c/d/e/f.
+	 * Each combination is unique from states_equal() point of view.
+	 * Explored states checkpoint is created after each iterator next call.
+	 * Iterator convergence logic expects that eventually current state
+	 * would get equal to one of the explored states and thus loop
+	 * exploration would be finished (at-least for a specific path).
+	 * Verifier evicts explored states with high miss to hit ratio
+	 * to to avoid comparing current state with too many explored
+	 * states per instruction.
+	 * This test is designed to "stress test" eviction policy defined using formula:
+	 *
+	 *    sl->miss_cnt > sl->hit_cnt * N + N // if true sl->state is evicted
+	 *
+	 * Currently N is set to 64, which allows for 6 variables in this test.
+	 */
+	asm volatile (
+		"r6 = 0;"                  /* a */
+		"r7 = 0;"                  /* b */
+		"r8 = 0;"                  /* c */
+		"*(u64 *)(r10 - 24) = r6;" /* d */
+		"*(u64 *)(r10 - 32) = r6;" /* e */
+		"*(u64 *)(r10 - 40) = r6;" /* f */
+		"r9 = 0;"                  /* sum */
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto loop_end_%=;"
+
+		"*(u64 *)(r10 - 16) = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"r6 = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"r7 = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"r8 = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"*(u64 *)(r10 - 24) = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"*(u64 *)(r10 - 32) = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"*(u64 *)(r10 - 40) = r0;"
+
+		"if r6 == 0 goto +1;"
+		"r9 += 1;"
+		"if r7 == 0 goto +1;"
+		"r9 += 1;"
+		"if r8 == 0 goto +1;"
+		"r9 += 1;"
+		"r0 = *(u64 *)(r10 - 24);"
+		"if r0 == 0 goto +1;"
+		"r9 += 1;"
+		"r0 = *(u64 *)(r10 - 32);"
+		"if r0 == 0 goto +1;"
+		"r9 += 1;"
+		"r0 = *(u64 *)(r10 - 40);"
+		"if r0 == 0 goto +1;"
+		"r9 += 1;"
+
+		"goto loop_%=;"
+	"loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_map_lookup_elem),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy),
+		  __imm_addr(amap)
+		: __clobber_all
+	);
+}
+
 char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/iters_task_vma.c b/tools/testing/selftests/bpf/progs/iters_task_vma.c
index 44edecfdfaee..e085a51d153e 100644
--- a/tools/testing/selftests/bpf/progs/iters_task_vma.c
+++ b/tools/testing/selftests/bpf/progs/iters_task_vma.c
@@ -30,6 +30,7 @@ int iter_task_vma_for_each(const void *ctx)
 	bpf_for_each(task_vma, vma, task, 0) {
 		if (seen >= 1000)
 			break;
+		barrier_var(seen);
 
 		vm_ranges[seen].vm_start = vma->vm_start;
 		vm_ranges[seen].vm_end = vma->vm_end;