bpf: Move check_cfg() into cfg.c

verifier.c is huge. Move check_cfg(), compute_postorder(),
compute_scc() into cfg.c

Mechanical move. No functional changes.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260412152936.54262-4-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -983,6 +983,41 @@ __printf(3, 4) void verbose_linfo(struct bpf_verifier_env *env,
 		bpf_log(&env->log, "verifier bug: " fmt "\n", ##args);				\
 	})
 
+static inline void mark_prune_point(struct bpf_verifier_env *env, int idx)
+{
+	env->insn_aux_data[idx].prune_point = true;
+}
+
+static inline bool bpf_is_prune_point(struct bpf_verifier_env *env, int insn_idx)
+{
+	return env->insn_aux_data[insn_idx].prune_point;
+}
+
+static inline void mark_force_checkpoint(struct bpf_verifier_env *env, int idx)
+{
+	env->insn_aux_data[idx].force_checkpoint = true;
+}
+
+static inline bool bpf_is_force_checkpoint(struct bpf_verifier_env *env, int insn_idx)
+{
+	return env->insn_aux_data[insn_idx].force_checkpoint;
+}
+
+static inline void mark_calls_callback(struct bpf_verifier_env *env, int idx)
+{
+	env->insn_aux_data[idx].calls_callback = true;
+}
+
+static inline bool bpf_calls_callback(struct bpf_verifier_env *env, int insn_idx)
+{
+	return env->insn_aux_data[insn_idx].calls_callback;
+}
+
+static inline void mark_jmp_point(struct bpf_verifier_env *env, int idx)
+{
+	env->insn_aux_data[idx].jmp_point = true;
+}
+
 static inline struct bpf_func_state *cur_func(struct bpf_verifier_env *env)
 {
 	struct bpf_verifier_state *cur = env->cur_state;
@@ -1179,13 +1214,91 @@ struct bpf_subprog_info *bpf_find_containing_subprog(struct bpf_verifier_env *en
 int bpf_jmp_offset(struct bpf_insn *insn);
 struct bpf_iarray *bpf_insn_successors(struct bpf_verifier_env *env, u32 idx);
 void bpf_fmt_stack_mask(char *buf, ssize_t buf_sz, u64 stack_mask);
-bool bpf_calls_callback(struct bpf_verifier_env *env, int insn_idx);
 bool bpf_subprog_is_global(const struct bpf_verifier_env *env, int subprog);
 
 int bpf_find_subprog(struct bpf_verifier_env *env, int off);
 int bpf_compute_const_regs(struct bpf_verifier_env *env);
 int bpf_prune_dead_branches(struct bpf_verifier_env *env);
+int bpf_check_cfg(struct bpf_verifier_env *env);
 int bpf_compute_postorder(struct bpf_verifier_env *env);
+int bpf_compute_scc(struct bpf_verifier_env *env);
+
+struct bpf_map_desc {
+	struct bpf_map *ptr;
+	int uid;
+};
+
+struct bpf_kfunc_call_arg_meta {
+	/* In parameters */
+	struct btf *btf;
+	u32 func_id;
+	u32 kfunc_flags;
+	const struct btf_type *func_proto;
+	const char *func_name;
+	/* Out parameters */
+	u32 ref_obj_id;
+	u8 release_regno;
+	bool r0_rdonly;
+	u32 ret_btf_id;
+	u64 r0_size;
+	u32 subprogno;
+	struct {
+		u64 value;
+		bool found;
+	} arg_constant;
+
+	/* arg_{btf,btf_id,owning_ref} are used by kfunc-specific handling,
+	 * generally to pass info about user-defined local kptr types to later
+	 * verification logic
+	 *   bpf_obj_drop/bpf_percpu_obj_drop
+	 *     Record the local kptr type to be drop'd
+	 *   bpf_refcount_acquire (via KF_ARG_PTR_TO_REFCOUNTED_KPTR arg type)
+	 *     Record the local kptr type to be refcount_incr'd and use
+	 *     arg_owning_ref to determine whether refcount_acquire should be
+	 *     fallible
+	 */
+	struct btf *arg_btf;
+	u32 arg_btf_id;
+	bool arg_owning_ref;
+	bool arg_prog;
+
+	struct {
+		struct btf_field *field;
+	} arg_list_head;
+	struct {
+		struct btf_field *field;
+	} arg_rbtree_root;
+	struct {
+		enum bpf_dynptr_type type;
+		u32 id;
+		u32 ref_obj_id;
+	} initialized_dynptr;
+	struct {
+		u8 spi;
+		u8 frameno;
+	} iter;
+	struct bpf_map_desc map;
+	u64 mem_size;
+};
+
+int bpf_get_helper_proto(struct bpf_verifier_env *env, int func_id,
+			 const struct bpf_func_proto **ptr);
+int bpf_fetch_kfunc_arg_meta(struct bpf_verifier_env *env, s32 func_id,
+			     s16 offset, struct bpf_kfunc_call_arg_meta *meta);
+bool bpf_is_async_callback_calling_insn(struct bpf_insn *insn);
+bool bpf_is_sync_callback_calling_insn(struct bpf_insn *insn);
+static inline bool bpf_is_iter_next_kfunc(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_ITER_NEXT;
+}
+
+static inline bool bpf_is_kfunc_sleepable(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_SLEEPABLE;
+}
+bool bpf_is_kfunc_pkt_changing(struct bpf_kfunc_call_arg_meta *meta);
+struct bpf_iarray *bpf_iarray_realloc(struct bpf_iarray *old, size_t n_elem);
+int bpf_copy_insn_array_uniq(struct bpf_map *map, u32 start, u32 end, u32 *off);
 bool bpf_insn_is_cond_jump(u8 code);
 bool bpf_is_may_goto_insn(struct bpf_insn *insn);
 

kernel/bpf/Makefile

@@ -11,7 +11,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o bpf_insn_array.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
-obj-$(CONFIG_BPF_SYSCALL) += fixups.o
+obj-$(CONFIG_BPF_SYSCALL) += fixups.o cfg.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o

kernel/bpf/cfg.c

@@ -0,0 +1,872 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <linux/bpf.h>
+#include <linux/bpf_verifier.h>
+#include <linux/filter.h>
+#include <linux/sort.h>
+
+#define verbose(env, fmt, args...) bpf_verifier_log_write(env, fmt, ##args)
+
+/* non-recursive DFS pseudo code
+ * 1  procedure DFS-iterative(G,v):
+ * 2      label v as discovered
+ * 3      let S be a stack
+ * 4      S.push(v)
+ * 5      while S is not empty
+ * 6            t <- S.peek()
+ * 7            if t is what we're looking for:
+ * 8                return t
+ * 9            for all edges e in G.adjacentEdges(t) do
+ * 10               if edge e is already labelled
+ * 11                   continue with the next edge
+ * 12               w <- G.adjacentVertex(t,e)
+ * 13               if vertex w is not discovered and not explored
+ * 14                   label e as tree-edge
+ * 15                   label w as discovered
+ * 16                   S.push(w)
+ * 17                   continue at 5
+ * 18               else if vertex w is discovered
+ * 19                   label e as back-edge
+ * 20               else
+ * 21                   // vertex w is explored
+ * 22                   label e as forward- or cross-edge
+ * 23           label t as explored
+ * 24           S.pop()
+ *
+ * convention:
+ * 0x10 - discovered
+ * 0x11 - discovered and fall-through edge labelled
+ * 0x12 - discovered and fall-through and branch edges labelled
+ * 0x20 - explored
+ */
+
+enum {
+	DISCOVERED = 0x10,
+	EXPLORED = 0x20,
+	FALLTHROUGH = 1,
+	BRANCH = 2,
+};
+
+
+static void mark_subprog_changes_pkt_data(struct bpf_verifier_env *env, int off)
+{
+	struct bpf_subprog_info *subprog;
+
+	subprog = bpf_find_containing_subprog(env, off);
+	subprog->changes_pkt_data = true;
+}
+
+static void mark_subprog_might_sleep(struct bpf_verifier_env *env, int off)
+{
+	struct bpf_subprog_info *subprog;
+
+	subprog = bpf_find_containing_subprog(env, off);
+	subprog->might_sleep = true;
+}
+
+/* 't' is an index of a call-site.
+ * 'w' is a callee entry point.
+ * Eventually this function would be called when env->cfg.insn_state[w] == EXPLORED.
+ * Rely on DFS traversal order and absence of recursive calls to guarantee that
+ * callee's change_pkt_data marks would be correct at that moment.
+ */
+static void merge_callee_effects(struct bpf_verifier_env *env, int t, int w)
+{
+	struct bpf_subprog_info *caller, *callee;
+
+	caller = bpf_find_containing_subprog(env, t);
+	callee = bpf_find_containing_subprog(env, w);
+	caller->changes_pkt_data |= callee->changes_pkt_data;
+	caller->might_sleep |= callee->might_sleep;
+}
+
+enum {
+	DONE_EXPLORING = 0,
+	KEEP_EXPLORING = 1,
+};
+
+/* t, w, e - match pseudo-code above:
+ * t - index of current instruction
+ * w - next instruction
+ * e - edge
+ */
+static int push_insn(int t, int w, int e, struct bpf_verifier_env *env)
+{
+	int *insn_stack = env->cfg.insn_stack;
+	int *insn_state = env->cfg.insn_state;
+
+	if (e == FALLTHROUGH && insn_state[t] >= (DISCOVERED | FALLTHROUGH))
+		return DONE_EXPLORING;
+
+	if (e == BRANCH && insn_state[t] >= (DISCOVERED | BRANCH))
+		return DONE_EXPLORING;
+
+	if (w < 0 || w >= env->prog->len) {
+		verbose_linfo(env, t, "%d: ", t);
+		verbose(env, "jump out of range from insn %d to %d\n", t, w);
+		return -EINVAL;
+	}
+
+	if (e == BRANCH) {
+		/* mark branch target for state pruning */
+		mark_prune_point(env, w);
+		mark_jmp_point(env, w);
+	}
+
+	if (insn_state[w] == 0) {
+		/* tree-edge */
+		insn_state[t] = DISCOVERED | e;
+		insn_state[w] = DISCOVERED;
+		if (env->cfg.cur_stack >= env->prog->len)
+			return -E2BIG;
+		insn_stack[env->cfg.cur_stack++] = w;
+		return KEEP_EXPLORING;
+	} else if ((insn_state[w] & 0xF0) == DISCOVERED) {
+		if (env->bpf_capable)
+			return DONE_EXPLORING;
+		verbose_linfo(env, t, "%d: ", t);
+		verbose_linfo(env, w, "%d: ", w);
+		verbose(env, "back-edge from insn %d to %d\n", t, w);
+		return -EINVAL;
+	} else if (insn_state[w] == EXPLORED) {
+		/* forward- or cross-edge */
+		insn_state[t] = DISCOVERED | e;
+	} else {
+		verifier_bug(env, "insn state internal bug");
+		return -EFAULT;
+	}
+	return DONE_EXPLORING;
+}
+
+static int visit_func_call_insn(int t, struct bpf_insn *insns,
+				struct bpf_verifier_env *env,
+				bool visit_callee)
+{
+	int ret, insn_sz;
+	int w;
+
+	insn_sz = bpf_is_ldimm64(&insns[t]) ? 2 : 1;
+	ret = push_insn(t, t + insn_sz, FALLTHROUGH, env);
+	if (ret)
+		return ret;
+
+	mark_prune_point(env, t + insn_sz);
+	/* when we exit from subprog, we need to record non-linear history */
+	mark_jmp_point(env, t + insn_sz);
+
+	if (visit_callee) {
+		w = t + insns[t].imm + 1;
+		mark_prune_point(env, t);
+		merge_callee_effects(env, t, w);
+		ret = push_insn(t, w, BRANCH, env);
+	}
+	return ret;
+}
+
+struct bpf_iarray *bpf_iarray_realloc(struct bpf_iarray *old, size_t n_elem)
+{
+	size_t new_size = sizeof(struct bpf_iarray) + n_elem * sizeof(old->items[0]);
+	struct bpf_iarray *new;
+
+	new = kvrealloc(old, new_size, GFP_KERNEL_ACCOUNT);
+	if (!new) {
+		/* this is what callers always want, so simplify the call site */
+		kvfree(old);
+		return NULL;
+	}
+
+	new->cnt = n_elem;
+	return new;
+}
+
+static int copy_insn_array(struct bpf_map *map, u32 start, u32 end, u32 *items)
+{
+	struct bpf_insn_array_value *value;
+	u32 i;
+
+	for (i = start; i <= end; i++) {
+		value = map->ops->map_lookup_elem(map, &i);
+		/*
+		 * map_lookup_elem of an array map will never return an error,
+		 * but not checking it makes some static analysers to worry
+		 */
+		if (IS_ERR(value))
+			return PTR_ERR(value);
+		else if (!value)
+			return -EINVAL;
+		items[i - start] = value->xlated_off;
+	}
+	return 0;
+}
+
+static int cmp_ptr_to_u32(const void *a, const void *b)
+{
+	return *(u32 *)a - *(u32 *)b;
+}
+
+static int sort_insn_array_uniq(u32 *items, int cnt)
+{
+	int unique = 1;
+	int i;
+
+	sort(items, cnt, sizeof(items[0]), cmp_ptr_to_u32, NULL);
+
+	for (i = 1; i < cnt; i++)
+		if (items[i] != items[unique - 1])
+			items[unique++] = items[i];
+
+	return unique;
+}
+
+/*
+ * sort_unique({map[start], ..., map[end]}) into off
+ */
+int bpf_copy_insn_array_uniq(struct bpf_map *map, u32 start, u32 end, u32 *off)
+{
+	u32 n = end - start + 1;
+	int err;
+
+	err = copy_insn_array(map, start, end, off);
+	if (err)
+		return err;
+
+	return sort_insn_array_uniq(off, n);
+}
+
+/*
+ * Copy all unique offsets from the map
+ */
+static struct bpf_iarray *jt_from_map(struct bpf_map *map)
+{
+	struct bpf_iarray *jt;
+	int err;
+	int n;
+
+	jt = bpf_iarray_realloc(NULL, map->max_entries);
+	if (!jt)
+		return ERR_PTR(-ENOMEM);
+
+	n = bpf_copy_insn_array_uniq(map, 0, map->max_entries - 1, jt->items);
+	if (n < 0) {
+		err = n;
+		goto err_free;
+	}
+	if (n == 0) {
+		err = -EINVAL;
+		goto err_free;
+	}
+	jt->cnt = n;
+	return jt;
+
+err_free:
+	kvfree(jt);
+	return ERR_PTR(err);
+}
+
+/*
+ * Find and collect all maps which fit in the subprog. Return the result as one
+ * combined jump table in jt->items (allocated with kvcalloc)
+ */
+static struct bpf_iarray *jt_from_subprog(struct bpf_verifier_env *env,
+					  int subprog_start, int subprog_end)
+{
+	struct bpf_iarray *jt = NULL;
+	struct bpf_map *map;
+	struct bpf_iarray *jt_cur;
+	int i;
+
+	for (i = 0; i < env->insn_array_map_cnt; i++) {
+		/*
+		 * TODO (when needed): collect only jump tables, not static keys
+		 * or maps for indirect calls
+		 */
+		map = env->insn_array_maps[i];
+
+		jt_cur = jt_from_map(map);
+		if (IS_ERR(jt_cur)) {
+			kvfree(jt);
+			return jt_cur;
+		}
+
+		/*
+		 * This is enough to check one element. The full table is
+		 * checked to fit inside the subprog later in create_jt()
+		 */
+		if (jt_cur->items[0] >= subprog_start && jt_cur->items[0] < subprog_end) {
+			u32 old_cnt = jt ? jt->cnt : 0;
+			jt = bpf_iarray_realloc(jt, old_cnt + jt_cur->cnt);
+			if (!jt) {
+				kvfree(jt_cur);
+				return ERR_PTR(-ENOMEM);
+			}
+			memcpy(jt->items + old_cnt, jt_cur->items, jt_cur->cnt << 2);
+		}
+
+		kvfree(jt_cur);
+	}
+
+	if (!jt) {
+		verbose(env, "no jump tables found for subprog starting at %u\n", subprog_start);
+		return ERR_PTR(-EINVAL);
+	}
+
+	jt->cnt = sort_insn_array_uniq(jt->items, jt->cnt);
+	return jt;
+}
+
+static struct bpf_iarray *
+create_jt(int t, struct bpf_verifier_env *env)
+{
+	struct bpf_subprog_info *subprog;
+	int subprog_start, subprog_end;
+	struct bpf_iarray *jt;
+	int i;
+
+	subprog = bpf_find_containing_subprog(env, t);
+	subprog_start = subprog->start;
+	subprog_end = (subprog + 1)->start;
+	jt = jt_from_subprog(env, subprog_start, subprog_end);
+	if (IS_ERR(jt))
+		return jt;
+
+	/* Check that the every element of the jump table fits within the given subprogram */
+	for (i = 0; i < jt->cnt; i++) {
+		if (jt->items[i] < subprog_start || jt->items[i] >= subprog_end) {
+			verbose(env, "jump table for insn %d points outside of the subprog [%u,%u]\n",
+					t, subprog_start, subprog_end);
+			kvfree(jt);
+			return ERR_PTR(-EINVAL);
+		}
+	}
+
+	return jt;
+}
+
+/* "conditional jump with N edges" */
+static int visit_gotox_insn(int t, struct bpf_verifier_env *env)
+{
+	int *insn_stack = env->cfg.insn_stack;
+	int *insn_state = env->cfg.insn_state;
+	bool keep_exploring = false;
+	struct bpf_iarray *jt;
+	int i, w;
+
+	jt = env->insn_aux_data[t].jt;
+	if (!jt) {
+		jt = create_jt(t, env);
+		if (IS_ERR(jt))
+			return PTR_ERR(jt);
+
+		env->insn_aux_data[t].jt = jt;
+	}
+
+	mark_prune_point(env, t);
+	for (i = 0; i < jt->cnt; i++) {
+		w = jt->items[i];
+		if (w < 0 || w >= env->prog->len) {
+			verbose(env, "indirect jump out of range from insn %d to %d\n", t, w);
+			return -EINVAL;
+		}
+
+		mark_jmp_point(env, w);
+
+		/* EXPLORED || DISCOVERED */
+		if (insn_state[w])
+			continue;
+
+		if (env->cfg.cur_stack >= env->prog->len)
+			return -E2BIG;
+
+		insn_stack[env->cfg.cur_stack++] = w;
+		insn_state[w] |= DISCOVERED;
+		keep_exploring = true;
+	}
+
+	return keep_exploring ? KEEP_EXPLORING : DONE_EXPLORING;
+}
+
+/*
+ * Instructions that can abnormally return from a subprog (tail_call
+ * upon success, ld_{abs,ind} upon load failure) have a hidden exit
+ * that the verifier must account for.
+ */
+static int visit_abnormal_return_insn(struct bpf_verifier_env *env, int t)
+{
+	struct bpf_subprog_info *subprog;
+	struct bpf_iarray *jt;
+
+	if (env->insn_aux_data[t].jt)
+		return 0;
+
+	jt = bpf_iarray_realloc(NULL, 2);
+	if (!jt)
+		return -ENOMEM;
+
+	subprog = bpf_find_containing_subprog(env, t);
+	jt->items[0] = t + 1;
+	jt->items[1] = subprog->exit_idx;
+	env->insn_aux_data[t].jt = jt;
+	return 0;
+}
+
+/* Visits the instruction at index t and returns one of the following:
+ *  < 0 - an error occurred
+ *  DONE_EXPLORING - the instruction was fully explored
+ *  KEEP_EXPLORING - there is still work to be done before it is fully explored
+ */
+static int visit_insn(int t, struct bpf_verifier_env *env)
+{
+	struct bpf_insn *insns = env->prog->insnsi, *insn = &insns[t];
+	int ret, off, insn_sz;
+
+	if (bpf_pseudo_func(insn))
+		return visit_func_call_insn(t, insns, env, true);
+
+	/* All non-branch instructions have a single fall-through edge. */
+	if (BPF_CLASS(insn->code) != BPF_JMP &&
+	    BPF_CLASS(insn->code) != BPF_JMP32) {
+		if (BPF_CLASS(insn->code) == BPF_LD &&
+		    (BPF_MODE(insn->code) == BPF_ABS ||
+		     BPF_MODE(insn->code) == BPF_IND)) {
+			ret = visit_abnormal_return_insn(env, t);
+			if (ret)
+				return ret;
+		}
+		insn_sz = bpf_is_ldimm64(insn) ? 2 : 1;
+		return push_insn(t, t + insn_sz, FALLTHROUGH, env);
+	}
+
+	switch (BPF_OP(insn->code)) {
+	case BPF_EXIT:
+		return DONE_EXPLORING;
+
+	case BPF_CALL:
+		if (bpf_is_async_callback_calling_insn(insn))
+			/* Mark this call insn as a prune point to trigger
+			 * is_state_visited() check before call itself is
+			 * processed by __check_func_call(). Otherwise new
+			 * async state will be pushed for further exploration.
+			 */
+			mark_prune_point(env, t);
+		/* For functions that invoke callbacks it is not known how many times
+		 * callback would be called. Verifier models callback calling functions
+		 * by repeatedly visiting callback bodies and returning to origin call
+		 * instruction.
+		 * In order to stop such iteration verifier needs to identify when a
+		 * state identical some state from a previous iteration is reached.
+		 * Check below forces creation of checkpoint before callback calling
+		 * instruction to allow search for such identical states.
+		 */
+		if (bpf_is_sync_callback_calling_insn(insn)) {
+			mark_calls_callback(env, t);
+			mark_force_checkpoint(env, t);
+			mark_prune_point(env, t);
+			mark_jmp_point(env, t);
+		}
+		if (bpf_helper_call(insn)) {
+			const struct bpf_func_proto *fp;
+
+			ret = bpf_get_helper_proto(env, insn->imm, &fp);
+			/* If called in a non-sleepable context program will be
+			 * rejected anyway, so we should end up with precise
+			 * sleepable marks on subprogs, except for dead code
+			 * elimination.
+			 */
+			if (ret == 0 && fp->might_sleep)
+				mark_subprog_might_sleep(env, t);
+			if (bpf_helper_changes_pkt_data(insn->imm))
+				mark_subprog_changes_pkt_data(env, t);
+			if (insn->imm == BPF_FUNC_tail_call) {
+				ret = visit_abnormal_return_insn(env, t);
+				if (ret)
+					return ret;
+			}
+		} else if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
+			struct bpf_kfunc_call_arg_meta meta;
+
+			ret = bpf_fetch_kfunc_arg_meta(env, insn->imm, insn->off, &meta);
+			if (ret == 0 && bpf_is_iter_next_kfunc(&meta)) {
+				mark_prune_point(env, t);
+				/* Checking and saving state checkpoints at iter_next() call
+				 * is crucial for fast convergence of open-coded iterator loop
+				 * logic, so we need to force it. If we don't do that,
+				 * is_state_visited() might skip saving a checkpoint, causing
+				 * unnecessarily long sequence of not checkpointed
+				 * instructions and jumps, leading to exhaustion of jump
+				 * history buffer, and potentially other undesired outcomes.
+				 * It is expected that with correct open-coded iterators
+				 * convergence will happen quickly, so we don't run a risk of
+				 * exhausting memory.
+				 */
+				mark_force_checkpoint(env, t);
+			}
+			/* Same as helpers, if called in a non-sleepable context
+			 * program will be rejected anyway, so we should end up
+			 * with precise sleepable marks on subprogs, except for
+			 * dead code elimination.
+			 */
+			if (ret == 0 && bpf_is_kfunc_sleepable(&meta))
+				mark_subprog_might_sleep(env, t);
+			if (ret == 0 && bpf_is_kfunc_pkt_changing(&meta))
+				mark_subprog_changes_pkt_data(env, t);
+		}
+		return visit_func_call_insn(t, insns, env, insn->src_reg == BPF_PSEUDO_CALL);
+
+	case BPF_JA:
+		if (BPF_SRC(insn->code) == BPF_X)
+			return visit_gotox_insn(t, env);
+
+		if (BPF_CLASS(insn->code) == BPF_JMP)
+			off = insn->off;
+		else
+			off = insn->imm;
+
+		/* unconditional jump with single edge */
+		ret = push_insn(t, t + off + 1, FALLTHROUGH, env);
+		if (ret)
+			return ret;
+
+		mark_prune_point(env, t + off + 1);
+		mark_jmp_point(env, t + off + 1);
+
+		return ret;
+
+	default:
+		/* conditional jump with two edges */
+		mark_prune_point(env, t);
+		if (bpf_is_may_goto_insn(insn))
+			mark_force_checkpoint(env, t);
+
+		ret = push_insn(t, t + 1, FALLTHROUGH, env);
+		if (ret)
+			return ret;
+
+		return push_insn(t, t + insn->off + 1, BRANCH, env);
+	}
+}
+
+/* non-recursive depth-first-search to detect loops in BPF program
+ * loop == back-edge in directed graph
+ */
+int bpf_check_cfg(struct bpf_verifier_env *env)
+{
+	int insn_cnt = env->prog->len;
+	int *insn_stack, *insn_state;
+	int ex_insn_beg, i, ret = 0;
+
+	insn_state = env->cfg.insn_state = kvzalloc_objs(int, insn_cnt,
+							 GFP_KERNEL_ACCOUNT);
+	if (!insn_state)
+		return -ENOMEM;
+
+	insn_stack = env->cfg.insn_stack = kvzalloc_objs(int, insn_cnt,
+							 GFP_KERNEL_ACCOUNT);
+	if (!insn_stack) {
+		kvfree(insn_state);
+		return -ENOMEM;
+	}
+
+	ex_insn_beg = env->exception_callback_subprog
+		      ? env->subprog_info[env->exception_callback_subprog].start
+		      : 0;
+
+	insn_state[0] = DISCOVERED; /* mark 1st insn as discovered */
+	insn_stack[0] = 0; /* 0 is the first instruction */
+	env->cfg.cur_stack = 1;
+
+walk_cfg:
+	while (env->cfg.cur_stack > 0) {
+		int t = insn_stack[env->cfg.cur_stack - 1];
+
+		ret = visit_insn(t, env);
+		switch (ret) {
+		case DONE_EXPLORING:
+			insn_state[t] = EXPLORED;
+			env->cfg.cur_stack--;
+			break;
+		case KEEP_EXPLORING:
+			break;
+		default:
+			if (ret > 0) {
+				verifier_bug(env, "visit_insn internal bug");
+				ret = -EFAULT;
+			}
+			goto err_free;
+		}
+	}
+
+	if (env->cfg.cur_stack < 0) {
+		verifier_bug(env, "pop stack internal bug");
+		ret = -EFAULT;
+		goto err_free;
+	}
+
+	if (ex_insn_beg && insn_state[ex_insn_beg] != EXPLORED) {
+		insn_state[ex_insn_beg] = DISCOVERED;
+		insn_stack[0] = ex_insn_beg;
+		env->cfg.cur_stack = 1;
+		goto walk_cfg;
+	}
+
+	for (i = 0; i < insn_cnt; i++) {
+		struct bpf_insn *insn = &env->prog->insnsi[i];
+
+		if (insn_state[i] != EXPLORED) {
+			verbose(env, "unreachable insn %d\n", i);
+			ret = -EINVAL;
+			goto err_free;
+		}
+		if (bpf_is_ldimm64(insn)) {
+			if (insn_state[i + 1] != 0) {
+				verbose(env, "jump into the middle of ldimm64 insn %d\n", i);
+				ret = -EINVAL;
+				goto err_free;
+			}
+			i++; /* skip second half of ldimm64 */
+		}
+	}
+	ret = 0; /* cfg looks good */
+	env->prog->aux->changes_pkt_data = env->subprog_info[0].changes_pkt_data;
+	env->prog->aux->might_sleep = env->subprog_info[0].might_sleep;
+
+err_free:
+	kvfree(insn_state);
+	kvfree(insn_stack);
+	env->cfg.insn_state = env->cfg.insn_stack = NULL;
+	return ret;
+}
+
+/*
+ * For each subprogram 'i' fill array env->cfg.insn_subprogram sub-range
+ * [env->subprog_info[i].postorder_start, env->subprog_info[i+1].postorder_start)
+ * with indices of 'i' instructions in postorder.
+ */
+int bpf_compute_postorder(struct bpf_verifier_env *env)
+{
+	u32 cur_postorder, i, top, stack_sz, s;
+	int *stack = NULL, *postorder = NULL, *state = NULL;
+	struct bpf_iarray *succ;
+
+	postorder = kvzalloc_objs(int, env->prog->len, GFP_KERNEL_ACCOUNT);
+	state = kvzalloc_objs(int, env->prog->len, GFP_KERNEL_ACCOUNT);
+	stack = kvzalloc_objs(int, env->prog->len, GFP_KERNEL_ACCOUNT);
+	if (!postorder || !state || !stack) {
+		kvfree(postorder);
+		kvfree(state);
+		kvfree(stack);
+		return -ENOMEM;
+	}
+	cur_postorder = 0;
+	for (i = 0; i < env->subprog_cnt; i++) {
+		env->subprog_info[i].postorder_start = cur_postorder;
+		stack[0] = env->subprog_info[i].start;
+		stack_sz = 1;
+		do {
+			top = stack[stack_sz - 1];
+			state[top] |= DISCOVERED;
+			if (state[top] & EXPLORED) {
+				postorder[cur_postorder++] = top;
+				stack_sz--;
+				continue;
+			}
+			succ = bpf_insn_successors(env, top);
+			for (s = 0; s < succ->cnt; ++s) {
+				if (!state[succ->items[s]]) {
+					stack[stack_sz++] = succ->items[s];
+					state[succ->items[s]] |= DISCOVERED;
+				}
+			}
+			state[top] |= EXPLORED;
+		} while (stack_sz);
+	}
+	env->subprog_info[i].postorder_start = cur_postorder;
+	env->cfg.insn_postorder = postorder;
+	env->cfg.cur_postorder = cur_postorder;
+	kvfree(stack);
+	kvfree(state);
+	return 0;
+}
+
+/*
+ * Compute strongly connected components (SCCs) on the CFG.
+ * Assign an SCC number to each instruction, recorded in env->insn_aux[*].scc.
+ * If instruction is a sole member of its SCC and there are no self edges,
+ * assign it SCC number of zero.
+ * Uses a non-recursive adaptation of Tarjan's algorithm for SCC computation.
+ */
+int bpf_compute_scc(struct bpf_verifier_env *env)
+{
+	const u32 NOT_ON_STACK = U32_MAX;
+
+	struct bpf_insn_aux_data *aux = env->insn_aux_data;
+	const u32 insn_cnt = env->prog->len;
+	int stack_sz, dfs_sz, err = 0;
+	u32 *stack, *pre, *low, *dfs;
+	u32 i, j, t, w;
+	u32 next_preorder_num;
+	u32 next_scc_id;
+	bool assign_scc;
+	struct bpf_iarray *succ;
+
+	next_preorder_num = 1;
+	next_scc_id = 1;
+	/*
+	 * - 'stack' accumulates vertices in DFS order, see invariant comment below;
+	 * - 'pre[t] == p' => preorder number of vertex 't' is 'p';
+	 * - 'low[t] == n' => smallest preorder number of the vertex reachable from 't' is 'n';
+	 * - 'dfs' DFS traversal stack, used to emulate explicit recursion.
+	 */
+	stack = kvcalloc(insn_cnt, sizeof(int), GFP_KERNEL_ACCOUNT);
+	pre = kvcalloc(insn_cnt, sizeof(int), GFP_KERNEL_ACCOUNT);
+	low = kvcalloc(insn_cnt, sizeof(int), GFP_KERNEL_ACCOUNT);
+	dfs = kvcalloc(insn_cnt, sizeof(*dfs), GFP_KERNEL_ACCOUNT);
+	if (!stack || !pre || !low || !dfs) {
+		err = -ENOMEM;
+		goto exit;
+	}
+	/*
+	 * References:
+	 * [1] R. Tarjan "Depth-First Search and Linear Graph Algorithms"
+	 * [2] D. J. Pearce "A Space-Efficient Algorithm for Finding Strongly Connected Components"
+	 *
+	 * The algorithm maintains the following invariant:
+	 * - suppose there is a path 'u' ~> 'v', such that 'pre[v] < pre[u]';
+	 * - then, vertex 'u' remains on stack while vertex 'v' is on stack.
+	 *
+	 * Consequently:
+	 * - If 'low[v] < pre[v]', there is a path from 'v' to some vertex 'u',
+	 *   such that 'pre[u] == low[v]'; vertex 'u' is currently on the stack,
+	 *   and thus there is an SCC (loop) containing both 'u' and 'v'.
+	 * - If 'low[v] == pre[v]', loops containing 'v' have been explored,
+	 *   and 'v' can be considered the root of some SCC.
+	 *
+	 * Here is a pseudo-code for an explicitly recursive version of the algorithm:
+	 *
+	 *    NOT_ON_STACK = insn_cnt + 1
+	 *    pre = [0] * insn_cnt
+	 *    low = [0] * insn_cnt
+	 *    scc = [0] * insn_cnt
+	 *    stack = []
+	 *
+	 *    next_preorder_num = 1
+	 *    next_scc_id = 1
+	 *
+	 *    def recur(w):
+	 *        nonlocal next_preorder_num
+	 *        nonlocal next_scc_id
+	 *
+	 *        pre[w] = next_preorder_num
+	 *        low[w] = next_preorder_num
+	 *        next_preorder_num += 1
+	 *        stack.append(w)
+	 *        for s in successors(w):
+	 *            # Note: for classic algorithm the block below should look as:
+	 *            #
+	 *            # if pre[s] == 0:
+	 *            #     recur(s)
+	 *            #     low[w] = min(low[w], low[s])
+	 *            # elif low[s] != NOT_ON_STACK:
+	 *            #     low[w] = min(low[w], pre[s])
+	 *            #
+	 *            # But replacing both 'min' instructions with 'low[w] = min(low[w], low[s])'
+	 *            # does not break the invariant and makes iterative version of the algorithm
+	 *            # simpler. See 'Algorithm #3' from [2].
+	 *
+	 *            # 's' not yet visited
+	 *            if pre[s] == 0:
+	 *                recur(s)
+	 *            # if 's' is on stack, pick lowest reachable preorder number from it;
+	 *            # if 's' is not on stack 'low[s] == NOT_ON_STACK > low[w]',
+	 *            # so 'min' would be a noop.
+	 *            low[w] = min(low[w], low[s])
+	 *
+	 *        if low[w] == pre[w]:
+	 *            # 'w' is the root of an SCC, pop all vertices
+	 *            # below 'w' on stack and assign same SCC to them.
+	 *            while True:
+	 *                t = stack.pop()
+	 *                low[t] = NOT_ON_STACK
+	 *                scc[t] = next_scc_id
+	 *                if t == w:
+	 *                    break
+	 *            next_scc_id += 1
+	 *
+	 *    for i in range(0, insn_cnt):
+	 *        if pre[i] == 0:
+	 *            recur(i)
+	 *
+	 * Below implementation replaces explicit recursion with array 'dfs'.
+	 */
+	for (i = 0; i < insn_cnt; i++) {
+		if (pre[i])
+			continue;
+		stack_sz = 0;
+		dfs_sz = 1;
+		dfs[0] = i;
+dfs_continue:
+		while (dfs_sz) {
+			w = dfs[dfs_sz - 1];
+			if (pre[w] == 0) {
+				low[w] = next_preorder_num;
+				pre[w] = next_preorder_num;
+				next_preorder_num++;
+				stack[stack_sz++] = w;
+			}
+			/* Visit 'w' successors */
+			succ = bpf_insn_successors(env, w);
+			for (j = 0; j < succ->cnt; ++j) {
+				if (pre[succ->items[j]]) {
+					low[w] = min(low[w], low[succ->items[j]]);
+				} else {
+					dfs[dfs_sz++] = succ->items[j];
+					goto dfs_continue;
+				}
+			}
+			/*
+			 * Preserve the invariant: if some vertex above in the stack
+			 * is reachable from 'w', keep 'w' on the stack.
+			 */
+			if (low[w] < pre[w]) {
+				dfs_sz--;
+				goto dfs_continue;
+			}
+			/*
+			 * Assign SCC number only if component has two or more elements,
+			 * or if component has a self reference, or if instruction is a
+			 * callback calling function (implicit loop).
+			 */
+			assign_scc = stack[stack_sz - 1] != w;	/* two or more elements? */
+			for (j = 0; j < succ->cnt; ++j) {	/* self reference? */
+				if (succ->items[j] == w) {
+					assign_scc = true;
+					break;
+				}
+			}
+			if (bpf_calls_callback(env, w)) /* implicit loop? */
+				assign_scc = true;
+			/* Pop component elements from stack */
+			do {
+				t = stack[--stack_sz];
+				low[t] = NOT_ON_STACK;
+				if (assign_scc)
+					aux[t].scc = next_scc_id;
+			} while (t != w);
+			if (assign_scc)
+				next_scc_id++;
+			dfs_sz--;
+		}
+	}
+	env->scc_info = kvzalloc_objs(*env->scc_info, next_scc_id,
+				      GFP_KERNEL_ACCOUNT);
+	if (!env->scc_info) {
+		err = -ENOMEM;
+		goto exit;
+	}
+	env->scc_cnt = next_scc_id;
+exit:
+	kvfree(stack);
+	kvfree(pre);
+	kvfree(low);
+	kvfree(dfs);
+	return err;
+}