diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e1848a2a7230..d61f670f279d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -517,6 +517,12 @@ static bool is_ptr_cast_function(enum bpf_func_id func_id)
 		func_id == BPF_FUNC_skc_to_tcp_request_sock;
 }
 
+static bool is_callback_calling_function(enum bpf_func_id func_id)
+{
+	return func_id == BPF_FUNC_for_each_map_elem ||
+	       func_id == BPF_FUNC_timer_set_callback;
+}
+
 static bool is_cmpxchg_insn(const struct bpf_insn *insn)
 {
 	return BPF_CLASS(insn->code) == BPF_STX &&
@@ -1446,7 +1452,7 @@ static void __mark_reg_unknown(const struct bpf_verifier_env *env,
 	reg->type = SCALAR_VALUE;
 	reg->var_off = tnum_unknown;
 	reg->frameno = 0;
-	reg->precise = env->subprog_cnt > 1 || !env->bpf_capable;
+	reg->precise = !env->bpf_capable;
 	__mark_reg_unbounded(reg);
 }
 
@@ -2267,6 +2273,11 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx,
 			 */
 			if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL && insn->imm == 0)
 				return -ENOTSUPP;
+			/* BPF helpers that invoke callback subprogs are
+			 * equivalent to BPF_PSEUDO_CALL above
+			 */
+			if (insn->src_reg == 0 && is_callback_calling_function(insn->imm))
+				return -ENOTSUPP;
 			/* regular helper call sets R0 */
 			*reg_mask &= ~1;
 			if (*reg_mask & 0x3f) {
@@ -2445,12 +2456,42 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int frame, int r
 		return 0;
 	if (!reg_mask && !stack_mask)
 		return 0;
+
 	for (;;) {
 		DECLARE_BITMAP(mask, 64);
 		u32 history = st->jmp_history_cnt;
 
 		if (env->log.level & BPF_LOG_LEVEL)
 			verbose(env, "last_idx %d first_idx %d\n", last_idx, first_idx);
+
+		if (last_idx < 0) {
+			/* we are at the entry into subprog, which
+			 * is expected for global funcs, but only if
+			 * requested precise registers are R1-R5
+			 * (which are global func's input arguments)
+			 */
+			if (st->curframe == 0 &&
+			    st->frame[0]->subprogno > 0 &&
+			    st->frame[0]->callsite == BPF_MAIN_FUNC &&
+			    stack_mask == 0 && (reg_mask & ~0x3e) == 0) {
+				bitmap_from_u64(mask, reg_mask);
+				for_each_set_bit(i, mask, 32) {
+					reg = &st->frame[0]->regs[i];
+					if (reg->type != SCALAR_VALUE) {
+						reg_mask &= ~(1u << i);
+						continue;
+					}
+					reg->precise = true;
+				}
+				return 0;
+			}
+
+			verbose(env, "BUG backtracing func entry subprog %d reg_mask %x stack_mask %llx\n",
+				st->frame[0]->subprogno, reg_mask, stack_mask);
+			WARN_ONCE(1, "verifier backtracking bug");
+			return -EFAULT;
+		}
+
 		for (i = last_idx;;) {
 			if (skip_first) {
 				err = 0;
@@ -5806,6 +5847,10 @@ typedef int (*set_callee_state_fn)(struct bpf_verifier_env *env,
 				   struct bpf_func_state *callee,
 				   int insn_idx);
 
+static int set_callee_state(struct bpf_verifier_env *env,
+			    struct bpf_func_state *caller,
+			    struct bpf_func_state *callee, int insn_idx);
+
 static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			     int *insn_idx, int subprog,
 			     set_callee_state_fn set_callee_state_cb)
@@ -5856,6 +5901,16 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 		}
 	}
 
+	/* set_callee_state is used for direct subprog calls, but we are
+	 * interested in validating only BPF helpers that can call subprogs as
+	 * callbacks
+	 */
+	if (set_callee_state_cb != set_callee_state && !is_callback_calling_function(insn->imm)) {
+		verbose(env, "verifier bug: helper %s#%d is not marked as callback-calling\n",
+			func_id_name(insn->imm), insn->imm);
+		return -EFAULT;
+	}
+
 	if (insn->code == (BPF_JMP | BPF_CALL) &&
 	    insn->src_reg == 0 &&
 	    insn->imm == BPF_FUNC_timer_set_callback) {
@@ -13209,6 +13264,8 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 			BPF_MAIN_FUNC /* callsite */,
 			0 /* frameno */,
 			subprog);
+	state->first_insn_idx = env->subprog_info[subprog].start;
+	state->last_insn_idx = -1;
 
 	regs = state->frame[state->curframe]->regs;
 	if (subprog || env->prog->type == BPF_PROG_TYPE_EXT) {