diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f5af759..ca17dccc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1122,10 +1122,6 @@ static void init_reg_state(struct bpf_verifier_env *env,
 	regs[BPF_REG_FP].type = PTR_TO_STACK;
 	mark_reg_known_zero(env, regs, BPF_REG_FP);
 	regs[BPF_REG_FP].frameno = state->frameno;
-
-	/* 1st arg to a function */
-	regs[BPF_REG_1].type = PTR_TO_CTX;
-	mark_reg_known_zero(env, regs, BPF_REG_1);
 }
 
 #define BPF_MAIN_FUNC (-1)
@@ -2739,8 +2735,8 @@ static int get_callee_stack_depth(struct bpf_verifier_env *env,
 }
 #endif
 
-static int check_ctx_reg(struct bpf_verifier_env *env,
-			 const struct bpf_reg_state *reg, int regno)
+int check_ctx_reg(struct bpf_verifier_env *env,
+		  const struct bpf_reg_state *reg, int regno)
 {
 	/* Access to ctx or passing it to a helper is only allowed in
 	 * its original, unmodified form.
@@ -3956,12 +3952,26 @@ static int release_reference(struct bpf_verifier_env *env,
 	return 0;
 }
 
+static void clear_caller_saved_regs(struct bpf_verifier_env *env,
+				    struct bpf_reg_state *regs)
+{
+	int i;
+
+	/* after the call registers r0 - r5 were scratched */
+	for (i = 0; i < CALLER_SAVED_REGS; i++) {
+		mark_reg_not_init(env, regs, caller_saved[i]);
+		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+	}
+}
+
 static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			   int *insn_idx)
 {
 	struct bpf_verifier_state *state = env->cur_state;
+	struct bpf_func_info_aux *func_info_aux;
 	struct bpf_func_state *caller, *callee;
 	int i, err, subprog, target_insn;
+	bool is_global = false;
 
 	if (state->curframe + 1 >= MAX_CALL_FRAMES) {
 		verbose(env, "the call stack of %d frames is too deep\n",
@@ -3984,6 +3994,32 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 		return -EFAULT;
 	}
 
+	func_info_aux = env->prog->aux->func_info_aux;
+	if (func_info_aux)
+		is_global = func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
+	err = btf_check_func_arg_match(env, subprog, caller->regs);
+	if (err == -EFAULT)
+		return err;
+	if (is_global) {
+		if (err) {
+			verbose(env, "Caller passes invalid args into func#%d\n",
+				subprog);
+			return err;
+		} else {
+			if (env->log.level & BPF_LOG_LEVEL)
+				verbose(env,
+					"Func#%d is global and valid. Skipping.\n",
+					subprog);
+			clear_caller_saved_regs(env, caller->regs);
+
+			/* All global functions return SCALAR_VALUE */
+			mark_reg_unknown(env, caller->regs, BPF_REG_0);
+
+			/* continue with next insn after call */
+			return 0;
+		}
+	}
+
 	callee = kzalloc(sizeof(*callee), GFP_KERNEL);
 	if (!callee)
 		return -ENOMEM;
@@ -4010,18 +4046,11 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	for (i = BPF_REG_1; i <= BPF_REG_5; i++)
 		callee->regs[i] = caller->regs[i];
 
-	/* after the call registers r0 - r5 were scratched */
-	for (i = 0; i < CALLER_SAVED_REGS; i++) {
-		mark_reg_not_init(env, caller->regs, caller_saved[i]);
-		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
-	}
+	clear_caller_saved_regs(env, caller->regs);
 
 	/* only increment it after check_reg_arg() finished */
 	state->curframe++;
 
-	if (btf_check_func_arg_match(env, subprog))
-		return -EINVAL;
-
 	/* and go analyze first insn of the callee */
 	*insn_idx = target_insn;
 
@@ -6771,12 +6800,13 @@ static int check_btf_func(struct bpf_verifier_env *env,
 
 		/* check type_id */
 		type = btf_type_by_id(btf, krecord[i].type_id);
-		if (!type || BTF_INFO_KIND(type->info) != BTF_KIND_FUNC) {
+		if (!type || !btf_type_is_func(type)) {
 			verbose(env, "invalid type id %d in func info",
 				krecord[i].type_id);
 			ret = -EINVAL;
 			goto err_free;
 		}
+		info_aux[i].linkage = BTF_INFO_VLEN(type->info);
 		prev_offset = krecord[i].insn_off;
 		urecord += urec_size;
 	}
@@ -7756,35 +7786,13 @@ static bool reg_type_mismatch(enum bpf_reg_type src, enum bpf_reg_type prev)
 
 static int do_check(struct bpf_verifier_env *env)
 {
-	struct bpf_verifier_state *state;
+	struct bpf_verifier_state *state = env->cur_state;
 	struct bpf_insn *insns = env->prog->insnsi;
 	struct bpf_reg_state *regs;
 	int insn_cnt = env->prog->len;
 	bool do_print_state = false;
 	int prev_insn_idx = -1;
 
-	env->prev_linfo = NULL;
-
-	state = kzalloc(sizeof(struct bpf_verifier_state), GFP_KERNEL);
-	if (!state)
-		return -ENOMEM;
-	state->curframe = 0;
-	state->speculative = false;
-	state->branches = 1;
-	state->frame[0] = kzalloc(sizeof(struct bpf_func_state), GFP_KERNEL);
-	if (!state->frame[0]) {
-		kfree(state);
-		return -ENOMEM;
-	}
-	env->cur_state = state;
-	init_func_state(env, state->frame[0],
-			BPF_MAIN_FUNC /* callsite */,
-			0 /* frameno */,
-			0 /* subprogno, zero == main subprog */);
-
-	if (btf_check_func_arg_match(env, 0))
-		return -EINVAL;
-
 	for (;;) {
 		struct bpf_insn *insn;
 		u8 class;
@@ -7862,7 +7870,7 @@ static int do_check(struct bpf_verifier_env *env)
 		}
 
 		regs = cur_regs(env);
-		env->insn_aux_data[env->insn_idx].seen = true;
+		env->insn_aux_data[env->insn_idx].seen = env->pass_cnt;
 		prev_insn_idx = env->insn_idx;
 
 		if (class == BPF_ALU || class == BPF_ALU64) {
@@ -8082,7 +8090,7 @@ static int do_check(struct bpf_verifier_env *env)
 					return err;
 
 				env->insn_idx++;
-				env->insn_aux_data[env->insn_idx].seen = true;
+				env->insn_aux_data[env->insn_idx].seen = env->pass_cnt;
 			} else {
 				verbose(env, "invalid BPF_LD mode\n");
 				return -EINVAL;
@@ -8095,7 +8103,6 @@ static int do_check(struct bpf_verifier_env *env)
 		env->insn_idx++;
 	}
 
-	env->prog->aux->stack_depth = env->subprog_info[0].stack_depth;
 	return 0;
 }
 
@@ -8372,7 +8379,7 @@ static int adjust_insn_aux_data(struct bpf_verifier_env *env,
 	memcpy(new_data + off + cnt - 1, old_data + off,
 	       sizeof(struct bpf_insn_aux_data) * (prog_len - off - cnt + 1));
 	for (i = off; i < off + cnt - 1; i++) {
-		new_data[i].seen = true;
+		new_data[i].seen = env->pass_cnt;
 		new_data[i].zext_dst = insn_has_def32(env, insn + i);
 	}
 	env->insn_aux_data = new_data;
@@ -9484,6 +9491,7 @@ static void free_states(struct bpf_verifier_env *env)
 		kfree(sl);
 		sl = sln;
 	}
+	env->free_list = NULL;
 
 	if (!env->explored_states)
 		return;
@@ -9497,11 +9505,159 @@ static void free_states(struct bpf_verifier_env *env)
 			kfree(sl);
 			sl = sln;
 		}
+		env->explored_states[i] = NULL;
+	}
+}
+
+/* The verifier is using insn_aux_data[] to store temporary data during
+ * verification and to store information for passes that run after the
+ * verification like dead code sanitization. do_check_common() for subprogram N
+ * may analyze many other subprograms. sanitize_insn_aux_data() clears all
+ * temporary data after do_check_common() finds that subprogram N cannot be
+ * verified independently. pass_cnt counts the number of times
+ * do_check_common() was run and insn->aux->seen tells the pass number
+ * insn_aux_data was touched. These variables are compared to clear temporary
+ * data from failed pass. For testing and experiments do_check_common() can be
+ * run multiple times even when prior attempt to verify is unsuccessful.
+ */
+static void sanitize_insn_aux_data(struct bpf_verifier_env *env)
+{
+	struct bpf_insn *insn = env->prog->insnsi;
+	struct bpf_insn_aux_data *aux;
+	int i, class;
+
+	for (i = 0; i < env->prog->len; i++) {
+		class = BPF_CLASS(insn[i].code);
+		if (class != BPF_LDX && class != BPF_STX)
+			continue;
+		aux = &env->insn_aux_data[i];
+		if (aux->seen != env->pass_cnt)
+			continue;
+		memset(aux, 0, offsetof(typeof(*aux), orig_idx));
+	}
+}
+
+static int do_check_common(struct bpf_verifier_env *env, int subprog)
+{
+	struct bpf_verifier_state *state;
+	struct bpf_reg_state *regs;
+	int ret, i;
+
+	env->prev_linfo = NULL;
+	env->pass_cnt++;
+
+	state = kzalloc(sizeof(struct bpf_verifier_state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+	state->curframe = 0;
+	state->speculative = false;
+	state->branches = 1;
+	state->frame[0] = kzalloc(sizeof(struct bpf_func_state), GFP_KERNEL);
+	if (!state->frame[0]) {
+		kfree(state);
+		return -ENOMEM;
+	}
+	env->cur_state = state;
+	init_func_state(env, state->frame[0],
+			BPF_MAIN_FUNC /* callsite */,
+			0 /* frameno */,
+			subprog);
+
+	regs = state->frame[state->curframe]->regs;
+	if (subprog) {
+		ret = btf_prepare_func_args(env, subprog, regs);
+		if (ret)
+			goto out;
+		for (i = BPF_REG_1; i <= BPF_REG_5; i++) {
+			if (regs[i].type == PTR_TO_CTX)
+				mark_reg_known_zero(env, regs, i);
+			else if (regs[i].type == SCALAR_VALUE)
+				mark_reg_unknown(env, regs, i);
+		}
+	} else {
+		/* 1st arg to a function */
+		regs[BPF_REG_1].type = PTR_TO_CTX;
+		mark_reg_known_zero(env, regs, BPF_REG_1);
+		ret = btf_check_func_arg_match(env, subprog, regs);
+		if (ret == -EFAULT)
+			/* unlikely verifier bug. abort.
+			 * ret == 0 and ret < 0 are sadly acceptable for
+			 * main() function due to backward compatibility.
+			 * Like socket filter program may be written as:
+			 * int bpf_prog(struct pt_regs *ctx)
+			 * and never dereference that ctx in the program.
+			 * 'struct pt_regs' is a type mismatch for socket
+			 * filter that should be using 'struct __sk_buff'.
+			 */
+			goto out;
 	}
 
-	kvfree(env->explored_states);
+	ret = do_check(env);
+out:
+	free_verifier_state(env->cur_state, true);
+	env->cur_state = NULL;
+	while (!pop_stack(env, NULL, NULL));
+	free_states(env);
+	if (ret)
+		/* clean aux data in case subprog was rejected */
+		sanitize_insn_aux_data(env);
+	return ret;
 }
 
+/* Verify all global functions in a BPF program one by one based on their BTF.
+ * All global functions must pass verification. Otherwise the whole program is rejected.
+ * Consider:
+ * int bar(int);
+ * int foo(int f)
+ * {
+ *    return bar(f);
+ * }
+ * int bar(int b)
+ * {
+ *    ...
+ * }
+ * foo() will be verified first for R1=any_scalar_value. During verification it
+ * will be assumed that bar() already verified successfully and call to bar()
+ * from foo() will be checked for type match only. Later bar() will be verified
+ * independently to check that it's safe for R1=any_scalar_value.
+ */
+static int do_check_subprogs(struct bpf_verifier_env *env)
+{
+	struct bpf_prog_aux *aux = env->prog->aux;
+	int i, ret;
+
+	if (!aux->func_info)
+		return 0;
+
+	for (i = 1; i < env->subprog_cnt; i++) {
+		if (aux->func_info_aux[i].linkage != BTF_FUNC_GLOBAL)
+			continue;
+		env->insn_idx = env->subprog_info[i].start;
+		WARN_ON_ONCE(env->insn_idx == 0);
+		ret = do_check_common(env, i);
+		if (ret) {
+			return ret;
+		} else if (env->log.level & BPF_LOG_LEVEL) {
+			verbose(env,
+				"Func#%d is safe for any args that match its prototype\n",
+				i);
+		}
+	}
+	return 0;
+}
+
+static int do_check_main(struct bpf_verifier_env *env)
+{
+	int ret;
+
+	env->insn_idx = 0;
+	ret = do_check_common(env, 0);
+	if (!ret)
+		env->prog->aux->stack_depth = env->subprog_info[0].stack_depth;
+	return ret;
+}
+
+
 static void print_verification_stats(struct bpf_verifier_env *env)
 {
 	int i;
@@ -9849,18 +10005,14 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr,
 	if (ret < 0)
 		goto skip_full_check;
 
-	ret = do_check(env);
-	if (env->cur_state) {
-		free_verifier_state(env->cur_state, true);
-		env->cur_state = NULL;
-	}
+	ret = do_check_subprogs(env);
+	ret = ret ?: do_check_main(env);
 
 	if (ret == 0 && bpf_prog_is_dev_bound(env->prog->aux))
 		ret = bpf_prog_offload_finalize(env);
 
 skip_full_check:
-	while (!pop_stack(env, NULL, NULL));
-	free_states(env);
+	kvfree(env->explored_states);
 
 	if (ret == 0)
 		ret = check_max_stack_depth(env);