Merge branch 'bpf-allow-void-return-type-for-global-subprogs'

Emil Tsalapatis says:

====================
bpf: Allow void return type for global subprogs

Global subprogs are currently not allowed to return void. Adjust
verifier logic to allow global functions with a void return type.
Exception callbacks are excluded from this change, and still require
a scalar return type.

Adding additional logic for void globals significantly complicates
check_return_code(), mainly because of how the new feature interacts
with bpf_throw(). To avoid complicating the code, refactor the return
value range validation logic into two separate functions, one for
program exits through BPF_EXIT and one for program exits through
bpf_throw(). The changes are non-functional.

Also adjust existing selftests that were ensuring that global subprogs
with void return types fail to verify. These tests should now load
successfully.

Patches 1-3 refactor check_return_code into two separate functions, one
for BPF_EXIT and one for bpf_throw(). No functional changes.

Patches 4-5 enable void globals in the verifier and add additional
selftests.

v5 -> v6
(https://lore.kernel.org/bpf/20260227154616.6846-1-emil@etsalapatis.com/)

Patch 1:

- Removed unused variables (kernel test robot)
- Add break; on empty default to suppress warning (kernel test robot)
- Added explanation on why change in switch statement for
  BPF_PROG_TYPE_TRACING in check_return_code is a no-op

Patches 2/3:

- Added From: tags to Eduard's patches and changed my Reviewed-by to
  Signed-off-by to properly denote patch route (submitting-patches.rst)
- Renamed check_subprogram_return_code for into check_global_subprog_return_code
  (Eduard)

Patch 4:

- Remove unnecessary subprog_is_global() check in check_return_code (Eduard)
- Fix indentation on patch 4 (AI)

Patch 5:

- Fix unused data in selftests (Eduard)

v4 -> v5
(https://lore.kernel.org/bpf/20260225033356.518313-1-emil@etsalapatis.com/)
- Split value validation logic from throw/nonthrow to main prog/subprog (Eduard)
- Turn return_retval_range() to bool and incorporate return_32bit in retval (Eduard)
- Adjust if-else chain in return_retval_range for cgroup programs into switch
  statement to bring it in line with the other program types

v3 -> v4
(https://lore.kernel.org/bpf/20260223215046.1706110-1-emil@etsalapatis.com/)
- Factor out bpf_throw() return value validation logic into its own
  function (Eduard)
- Validate the range of bpf_throw() return values from void globals (Eduard)
- Move new selftest to verifier_global_subprogs.c (Eduard)
- Remove unnecessary verifier_bug_if() statements (Eduard)
- Add new test to ensure void globals can call bpf_throw

v2 -> v3
(https://lore.kernel.org/bpf/20260210183257.217285-1-emil@etsalapatis.com/)
- Allow freplace for global programs that return void and add selftests (Kumar)

v1 -> v2
(https://lore.kernel.org/bpf/20260127231414.359283-1-emil@etsalapatis.com/)

- Only mark R0 as valid for non-void global functions (AI)
- Rename subprog_is_void to subprog_returns_void (Kumar)
- Add test that R0 is invalid after calling a void global (Alexei)
- Add check to ensure exception callbacks do not return void
and associated selftest

Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
====================

Link: https://patch.msgid.link/20260228184759.108145-1-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

11 files changed, 344 insertions, 129 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index c1e30096ea7b..090aa26d1c98 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -265,6 +265,7 @@ struct bpf_reference_state {
 struct bpf_retval_range {
 	s32 minval;
 	s32 maxval;
+	bool return_32bit;
 };
 
 /* state of the program:
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4872d2a6c42d..09fcbb125155 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -7836,15 +7836,16 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			tname, nargs, MAX_BPF_FUNC_REG_ARGS);
 		return -EINVAL;
 	}
-	/* check that function returns int, exception cb also requires this */
+	/* check that function is void or returns int, exception cb also requires this */
 	t = btf_type_by_id(btf, t->type);
 	while (btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
-	if (!btf_type_is_int(t) && !btf_is_any_enum(t)) {
+	if (!btf_type_is_void(t) && !btf_type_is_int(t) && !btf_is_any_enum(t)) {
 		if (!is_global)
 			return -EINVAL;
 		bpf_log(log,
-			"Global function %s() doesn't return scalar. Only those are supported.\n",
+			"Global function %s() return value not void or scalar. "
+			"Only those are supported.\n",
 			tname);
 		return -EINVAL;
 	}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 34f89ed29c47..d92cf2821657 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -444,6 +444,29 @@ static bool subprog_is_global(const struct bpf_verifier_env *env, int subprog)
 	return aux && aux[subprog].linkage == BTF_FUNC_GLOBAL;
 }
 
+static bool subprog_returns_void(struct bpf_verifier_env *env, int subprog)
+{
+	const struct btf_type *type, *func, *func_proto;
+	const struct btf *btf = env->prog->aux->btf;
+	u32 btf_id;
+
+	btf_id = env->prog->aux->func_info[subprog].type_id;
+
+	func = btf_type_by_id(btf, btf_id);
+	if (verifier_bug_if(!func, env, "btf_id %u not found", btf_id))
+		return false;
+
+	func_proto = btf_type_by_id(btf, func->type);
+	if (!func_proto)
+		return false;
+
+	type = btf_type_skip_modifiers(btf, func_proto->type, NULL);
+	if (!type)
+		return false;
+
+	return btf_type_is_void(type);
+}
+
 static const char *subprog_name(const struct bpf_verifier_env *env, int subprog)
 {
 	struct bpf_func_info *info;
@@ -2953,7 +2976,11 @@ static void init_reg_state(struct bpf_verifier_env *env,
 
 static struct bpf_retval_range retval_range(s32 minval, s32 maxval)
 {
-	return (struct bpf_retval_range){ minval, maxval };
+	/*
+	 * return_32bit is set to false by default and set explicitly
+	 * by the caller when necessary.
+	 */
+	return (struct bpf_retval_range){ minval, maxval, false };
 }
 
 #define BPF_MAIN_FUNC (-1)
@@ -10885,9 +10912,11 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 		subprog_aux(env, subprog)->called = true;
 		clear_caller_saved_regs(env, caller->regs);
 
-		/* All global functions return a 64-bit SCALAR_VALUE */
-		mark_reg_unknown(env, caller->regs, BPF_REG_0);
-		caller->regs[BPF_REG_0].subreg_def = DEF_NOT_SUBREG;
+		/* All non-void global functions return a 64-bit SCALAR_VALUE. */
+		if (!subprog_returns_void(env, subprog)) {
+			mark_reg_unknown(env, caller->regs, BPF_REG_0);
+			caller->regs[BPF_REG_0].subreg_def = DEF_NOT_SUBREG;
+		}
 
 		/* continue with next insn after call */
 		return 0;
@@ -11175,10 +11204,9 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
 	return is_rbtree_lock_required_kfunc(kfunc_btf_id);
 }
 
-static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg,
-				bool return_32bit)
+static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
 {
-	if (return_32bit)
+	if (range.return_32bit)
 		return range.minval <= reg->s32_min_value && reg->s32_max_value <= range.maxval;
 	else
 		return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
@@ -11222,7 +11250,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 			return err;
 
 		/* enforce R0 return value range, and bpf_callback_t returns 64bit */
-		if (!retval_range_within(callee->callback_ret_range, r0, false)) {
+		if (!retval_range_within(callee->callback_ret_range, r0)) {
 			verbose_invalid_scalar(env, r0, callee->callback_ret_range,
 					       "At callback return", "R0");
 			return -EINVAL;
@@ -17841,104 +17869,39 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	return 0;
 }
 
-static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
+
+static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_range *range)
 {
-	const char *exit_ctx = "At program exit";
-	struct tnum enforce_attach_type_range = tnum_unknown;
-	const struct bpf_prog *prog = env->prog;
-	struct bpf_reg_state *reg = reg_state(env, regno);
-	struct bpf_retval_range range = retval_range(0, 1);
 	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
-	int err;
-	struct bpf_func_state *frame = env->cur_state->frame[0];
-	const bool is_subprog = frame->subprogno;
-	bool return_32bit = false;
-	const struct btf_type *reg_type, *ret_type = NULL;
-
-	/* LSM and struct_ops func-ptr's return type could be "void" */
-	if (!is_subprog || frame->in_exception_callback_fn) {
-		switch (prog_type) {
-		case BPF_PROG_TYPE_LSM:
-			if (prog->expected_attach_type == BPF_LSM_CGROUP)
-				/* See below, can be 0 or 0-1 depending on hook. */
-				break;
-			if (!prog->aux->attach_func_proto->type)
-				return 0;
-			break;
-		case BPF_PROG_TYPE_STRUCT_OPS:
-			if (!prog->aux->attach_func_proto->type)
-				return 0;
 
-			if (frame->in_exception_callback_fn)
-				break;
+	/* Default return value range. */
+	*range = retval_range(0, 1);
 
-			/* Allow a struct_ops program to return a referenced kptr if it
-			 * matches the operator's return type and is in its unmodified
-			 * form. A scalar zero (i.e., a null pointer) is also allowed.
-			 */
-			reg_type = reg->btf ? btf_type_by_id(reg->btf, reg->btf_id) : NULL;
-			ret_type = btf_type_resolve_ptr(prog->aux->attach_btf,
-							prog->aux->attach_func_proto->type,
-							NULL);
-			if (ret_type && ret_type == reg_type && reg->ref_obj_id)
-				return __check_ptr_off_reg(env, reg, regno, false);
+	switch (prog_type) {
+	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
+		switch (env->prog->expected_attach_type) {
+		case BPF_CGROUP_UDP4_RECVMSG:
+		case BPF_CGROUP_UDP6_RECVMSG:
+		case BPF_CGROUP_UNIX_RECVMSG:
+		case BPF_CGROUP_INET4_GETPEERNAME:
+		case BPF_CGROUP_INET6_GETPEERNAME:
+		case BPF_CGROUP_UNIX_GETPEERNAME:
+		case BPF_CGROUP_INET4_GETSOCKNAME:
+		case BPF_CGROUP_INET6_GETSOCKNAME:
+		case BPF_CGROUP_UNIX_GETSOCKNAME:
+			*range = retval_range(1, 1);
+			break;
+		case BPF_CGROUP_INET4_BIND:
+		case BPF_CGROUP_INET6_BIND:
+			*range = retval_range(0, 3);
 			break;
 		default:
 			break;
 		}
-	}
-
-	/* eBPF calling convention is such that R0 is used
-	 * to return the value from eBPF program.
-	 * Make sure that it's readable at this time
-	 * of bpf_exit, which means that program wrote
-	 * something into it earlier
-	 */
-	err = check_reg_arg(env, regno, SRC_OP);
-	if (err)
-		return err;
-
-	if (is_pointer_value(env, regno)) {
-		verbose(env, "R%d leaks addr as return value\n", regno);
-		return -EACCES;
-	}
-
-	if (frame->in_async_callback_fn) {
-		exit_ctx = "At async callback return";
-		range = frame->callback_ret_range;
-		goto enforce_retval;
-	}
-
-	if (is_subprog && !frame->in_exception_callback_fn) {
-		if (reg->type != SCALAR_VALUE) {
-			verbose(env, "At subprogram exit the register R%d is not a scalar value (%s)\n",
-				regno, reg_type_str(env, reg->type));
-			return -EINVAL;
-		}
-		return 0;
-	}
-
-	switch (prog_type) {
-	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
-		if (env->prog->expected_attach_type == BPF_CGROUP_UDP4_RECVMSG ||
-		    env->prog->expected_attach_type == BPF_CGROUP_UDP6_RECVMSG ||
-		    env->prog->expected_attach_type == BPF_CGROUP_UNIX_RECVMSG ||
-		    env->prog->expected_attach_type == BPF_CGROUP_INET4_GETPEERNAME ||
-		    env->prog->expected_attach_type == BPF_CGROUP_INET6_GETPEERNAME ||
-		    env->prog->expected_attach_type == BPF_CGROUP_UNIX_GETPEERNAME ||
-		    env->prog->expected_attach_type == BPF_CGROUP_INET4_GETSOCKNAME ||
-		    env->prog->expected_attach_type == BPF_CGROUP_INET6_GETSOCKNAME ||
-		    env->prog->expected_attach_type == BPF_CGROUP_UNIX_GETSOCKNAME)
-			range = retval_range(1, 1);
-		if (env->prog->expected_attach_type == BPF_CGROUP_INET4_BIND ||
-		    env->prog->expected_attach_type == BPF_CGROUP_INET6_BIND)
-			range = retval_range(0, 3);
 		break;
 	case BPF_PROG_TYPE_CGROUP_SKB:
-		if (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {
-			range = retval_range(0, 3);
-			enforce_attach_type_range = tnum_range(2, 3);
-		}
+		if (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS)
+			*range = retval_range(0, 3);
 		break;
 	case BPF_PROG_TYPE_CGROUP_SOCK:
 	case BPF_PROG_TYPE_SOCK_OPS:
@@ -17948,72 +17911,164 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
 		break;
 	case BPF_PROG_TYPE_RAW_TRACEPOINT:
 		if (!env->prog->aux->attach_btf_id)
-			return 0;
-		range = retval_range(0, 0);
+			return false;
+		*range = retval_range(0, 0);
 		break;
 	case BPF_PROG_TYPE_TRACING:
 		switch (env->prog->expected_attach_type) {
 		case BPF_TRACE_FENTRY:
 		case BPF_TRACE_FEXIT:
 		case BPF_TRACE_FSESSION:
-			range = retval_range(0, 0);
+			*range = retval_range(0, 0);
 			break;
 		case BPF_TRACE_RAW_TP:
 		case BPF_MODIFY_RETURN:
-			return 0;
+			return false;
 		case BPF_TRACE_ITER:
-			break;
 		default:
-			return -ENOTSUPP;
+			break;
 		}
 		break;
 	case BPF_PROG_TYPE_KPROBE:
 		switch (env->prog->expected_attach_type) {
 		case BPF_TRACE_KPROBE_SESSION:
 		case BPF_TRACE_UPROBE_SESSION:
-			range = retval_range(0, 1);
 			break;
 		default:
-			return 0;
+			return false;
 		}
 		break;
 	case BPF_PROG_TYPE_SK_LOOKUP:
-		range = retval_range(SK_DROP, SK_PASS);
+		*range = retval_range(SK_DROP, SK_PASS);
 		break;
 
 	case BPF_PROG_TYPE_LSM:
 		if (env->prog->expected_attach_type != BPF_LSM_CGROUP) {
 			/* no range found, any return value is allowed */
-			if (!get_func_retval_range(env->prog, &range))
-				return 0;
+			if (!get_func_retval_range(env->prog, range))
+				return false;
 			/* no restricted range, any return value is allowed */
-			if (range.minval == S32_MIN && range.maxval == S32_MAX)
-				return 0;
-			return_32bit = true;
+			if (range->minval == S32_MIN && range->maxval == S32_MAX)
+				return false;
+			range->return_32bit = true;
 		} else if (!env->prog->aux->attach_func_proto->type) {
 			/* Make sure programs that attach to void
 			 * hooks don't try to modify return value.
 			 */
-			range = retval_range(1, 1);
+			*range = retval_range(1, 1);
 		}
 		break;
 
 	case BPF_PROG_TYPE_NETFILTER:
-		range = retval_range(NF_DROP, NF_ACCEPT);
+		*range = retval_range(NF_DROP, NF_ACCEPT);
 		break;
 	case BPF_PROG_TYPE_STRUCT_OPS:
-		if (!ret_type)
-			return 0;
-		range = retval_range(0, 0);
+		*range = retval_range(0, 0);
 		break;
 	case BPF_PROG_TYPE_EXT:
 		/* freplace program can return anything as its return value
 		 * depends on the to-be-replaced kernel func or bpf program.
 		 */
 	default:
+		return false;
+	}
+
+	/* Continue calculating. */
+
+	return true;
+}
+
+static bool program_returns_void(struct bpf_verifier_env *env)
+{
+	const struct bpf_prog *prog = env->prog;
+	enum bpf_prog_type prog_type = prog->type;
+
+	switch (prog_type) {
+	case BPF_PROG_TYPE_LSM:
+		/* See return_retval_range, for BPF_LSM_CGROUP can be 0 or 0-1 depending on hook. */
+		if (prog->expected_attach_type != BPF_LSM_CGROUP &&
+		    !prog->aux->attach_func_proto->type)
+			return true;
+		break;
+	case BPF_PROG_TYPE_STRUCT_OPS:
+		if (!prog->aux->attach_func_proto->type)
+			return true;
+		break;
+	case BPF_PROG_TYPE_EXT:
+		/*
+		 * If the actual program is an extension, let it
+		 * return void - attaching will succeed only if the
+		 * program being replaced also returns void, and since
+		 * it has passed verification its actual type doesn't matter.
+		 */
+		if (subprog_returns_void(env, 0))
+			return true;
+		break;
+	default:
+		break;
+	}
+	return false;
+}
+
+static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
+{
+	const char *exit_ctx = "At program exit";
+	struct tnum enforce_attach_type_range = tnum_unknown;
+	const struct bpf_prog *prog = env->prog;
+	struct bpf_reg_state *reg = reg_state(env, regno);
+	struct bpf_retval_range range = retval_range(0, 1);
+	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
+	struct bpf_func_state *frame = env->cur_state->frame[0];
+	const struct btf_type *reg_type, *ret_type = NULL;
+	int err;
+
+	/* LSM and struct_ops func-ptr's return type could be "void" */
+	if (!frame->in_async_callback_fn && program_returns_void(env))
 		return 0;
+
+	if (prog_type == BPF_PROG_TYPE_STRUCT_OPS) {
+		/* Allow a struct_ops program to return a referenced kptr if it
+		 * matches the operator's return type and is in its unmodified
+		 * form. A scalar zero (i.e., a null pointer) is also allowed.
+		 */
+		reg_type = reg->btf ? btf_type_by_id(reg->btf, reg->btf_id) : NULL;
+		ret_type = btf_type_resolve_ptr(prog->aux->attach_btf,
+						prog->aux->attach_func_proto->type,
+						NULL);
+		if (ret_type && ret_type == reg_type && reg->ref_obj_id)
+			return __check_ptr_off_reg(env, reg, regno, false);
+	}
+
+	/* eBPF calling convention is such that R0 is used
+	 * to return the value from eBPF program.
+	 * Make sure that it's readable at this time
+	 * of bpf_exit, which means that program wrote
+	 * something into it earlier
+	 */
+	err = check_reg_arg(env, regno, SRC_OP);
+	if (err)
+		return err;
+
+	if (is_pointer_value(env, regno)) {
+		verbose(env, "R%d leaks addr as return value\n", regno);
+		return -EACCES;
+	}
+
+	if (frame->in_async_callback_fn) {
+		exit_ctx = "At async callback return";
+		range = frame->callback_ret_range;
+		goto enforce_retval;
 	}
 
+	if (prog_type == BPF_PROG_TYPE_STRUCT_OPS && !ret_type)
+		return 0;
+
+	if (prog_type == BPF_PROG_TYPE_CGROUP_SKB && (env->prog->expected_attach_type == BPF_CGROUP_INET_EGRESS))
+		enforce_attach_type_range = tnum_range(2, 3);
+
+	if (!return_retval_range(env, &range))
+		return 0;
+
 enforce_retval:
 	if (reg->type != SCALAR_VALUE) {
 		verbose(env, "%s the register R%d is not a known value (%s)\n",
@@ -18025,10 +18080,9 @@ enforce_retval:
 	if (err)
 		return err;
 
-	if (!retval_range_within(range, reg, return_32bit)) {
+	if (!retval_range_within(range, reg)) {
 		verbose_invalid_scalar(env, reg, range, exit_ctx, reg_name);
-		if (!is_subprog &&
-		    prog->expected_attach_type == BPF_LSM_CGROUP &&
+		if (prog->expected_attach_type == BPF_LSM_CGROUP &&
 		    prog_type == BPF_PROG_TYPE_LSM &&
 		    !prog->aux->attach_func_proto->type)
 			verbose(env, "Note, BPF_LSM_CGROUP that attach to void LSM hooks can't modify return value!\n");
@@ -18041,6 +18095,33 @@ enforce_retval:
 	return 0;
 }
 
+static int check_global_subprog_return_code(struct bpf_verifier_env *env)
+{
+	struct bpf_reg_state *reg = reg_state(env, BPF_REG_0);
+	struct bpf_func_state *cur_frame = cur_func(env);
+	int err;
+
+	if (subprog_returns_void(env, cur_frame->subprogno))
+		return 0;
+
+	err = check_reg_arg(env, BPF_REG_0, SRC_OP);
+	if (err)
+		return err;
+
+	if (is_pointer_value(env, BPF_REG_0)) {
+		verbose(env, "R%d leaks addr as return value\n", BPF_REG_0);
+		return -EACCES;
+	}
+
+	if (reg->type != SCALAR_VALUE) {
+		verbose(env, "At subprogram exit the register R0 is not a scalar value (%s)\n",
+			reg_type_str(env, reg->type));
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static void mark_subprog_changes_pkt_data(struct bpf_verifier_env *env, int off)
 {
 	struct bpf_subprog_info *subprog;
@@ -20834,6 +20915,8 @@ static int process_bpf_exit_full(struct bpf_verifier_env *env,
 				 bool *do_print_state,
 				 bool exception_exit)
 {
+	struct bpf_func_state *cur_frame = cur_func(env);
+
 	/* We must do check_reference_leak here before
 	 * prepare_func_exit to handle the case when
 	 * state->curframe > 0, it may be a callback function,
@@ -20867,7 +20950,21 @@ static int process_bpf_exit_full(struct bpf_verifier_env *env,
 		return 0;
 	}
 
-	err = check_return_code(env, BPF_REG_0, "R0");
+	/*
+	 * Return from a regular global subprogram differs from return
+	 * from the main program or async/exception callback.
+	 * Main program exit implies return code restrictions
+	 * that depend on program type.
+	 * Exit from exception callback is equivalent to main program exit.
+	 * Exit from async callback implies return code restrictions
+	 * that depend on async scheduling mechanism.
+	 */
+	if (cur_frame->subprogno &&
+	    !cur_frame->in_async_callback_fn &&
+	    !cur_frame->in_exception_callback_fn)
+		err = check_global_subprog_return_code(env);
+	else
+		err = check_return_code(env, BPF_REG_0, "R0");
 	if (err)
 		return err;
 	return PROCESS_BPF_EXIT;
@@ -24506,10 +24603,18 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
 
 		if (subprog_is_exc_cb(env, subprog)) {
 			state->frame[0]->in_exception_callback_fn = true;
-			/* We have already ensured that the callback returns an integer, just
-			 * like all global subprogs. We need to determine it only has a single
-			 * scalar argument.
+
+			/*
+			 * Global functions are scalar or void, make sure
+			 * we return a scalar.
 			 */
+			if (subprog_returns_void(env, subprog)) {
+				verbose(env, "exception cb cannot return void\n");
+				ret = -EINVAL;
+				goto out;
+			}
+
+			/* Also ensure the callback only has a single scalar argument. */
 			if (sub->arg_cnt != 1 || sub->args[0].arg_type != ARG_ANYTHING) {
 				verbose(env, "exception cb only supports single integer argument\n");
 				ret = -EINVAL;
diff --git a/tools/testing/selftests/bpf/prog_tests/exceptions.c b/tools/testing/selftests/bpf/prog_tests/exceptions.c
index 516f4a13013c..84ab73e08b0e 100644
--- a/tools/testing/selftests/bpf/prog_tests/exceptions.c
+++ b/tools/testing/selftests/bpf/prog_tests/exceptions.c
@@ -83,6 +83,7 @@ static void test_exceptions_success(void)
 	RUN_SUCCESS(exception_assert_range_with, 1);
 	RUN_SUCCESS(exception_bad_assert_range, 0);
 	RUN_SUCCESS(exception_bad_assert_range_with, 10);
+	RUN_SUCCESS(exception_throw_from_void_global, 11);
 
 #define RUN_EXT(load_ret, attach_err, expr, msg, after_link)			  \
 	{									  \
diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
index f29fc789c14b..23d933f1aec6 100644
--- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
@@ -347,6 +347,17 @@ static void test_func_sockmap_update(void)
 				  prog_name, false, NULL);
 }
 
+static void test_func_replace_void(void)
+{
+	const char *prog_name[] = {
+		"freplace/foo",
+	};
+	test_fexit_bpf2bpf_common("./freplace_void.bpf.o",
+				  "./test_global_func7.bpf.o",
+				  ARRAY_SIZE(prog_name),
+				  prog_name, false, NULL);
+}
+
 static void test_obj_load_failure_common(const char *obj_file,
 					 const char *target_obj_file,
 					 const char *exp_msg)
@@ -432,6 +443,15 @@ static void test_func_replace_global_func(void)
 				  prog_name, false, NULL);
 }
 
+static void test_func_replace_int_with_void(void)
+{
+	/* Make sure we can't freplace with the wrong type */
+	test_obj_load_failure_common("freplace_int_with_void.bpf.o",
+				     "./test_global_func2.bpf.o",
+				     "Return type UNKNOWN of test_freplace_int_with_void()"
+				     " doesn't match type INT of global_func2()");
+}
+
 static int find_prog_btf_id(const char *name, __u32 attach_prog_fd)
 {
 	struct bpf_prog_info info = {};
@@ -597,4 +617,8 @@ void serial_test_fexit_bpf2bpf(void)
 		test_fentry_to_cgroup_bpf();
 	if (test__start_subtest("func_replace_progmap"))
 		test_func_replace_progmap();
+	if (test__start_subtest("freplace_int_with_void"))
+		test_func_replace_int_with_void();
+	if (test__start_subtest("freplace_void"))
+		test_func_replace_void();
 }
diff --git a/tools/testing/selftests/bpf/progs/exceptions.c b/tools/testing/selftests/bpf/progs/exceptions.c
index f09cd14d8e04..4206f59d7b86 100644
--- a/tools/testing/selftests/bpf/progs/exceptions.c
+++ b/tools/testing/selftests/bpf/progs/exceptions.c
@@ -109,6 +109,20 @@ int exception_tail_call(struct __sk_buff *ctx) {
 	return ret + 8;
 }
 
+__weak
+void throw_11(void)
+{
+	bpf_throw(11);
+}
+
+SEC("tc")
+int exception_throw_from_void_global(struct __sk_buff *ctx)
+{
+	throw_11();
+
+	return 0;
+}
+
 __noinline int exception_ext_global(struct __sk_buff *ctx)
 {
 	volatile int ret = 0;
diff --git a/tools/testing/selftests/bpf/progs/exceptions_fail.c b/tools/testing/selftests/bpf/progs/exceptions_fail.c
index 8a0fdff89927..275ad6fe4a04 100644
--- a/tools/testing/selftests/bpf/progs/exceptions_fail.c
+++ b/tools/testing/selftests/bpf/progs/exceptions_fail.c
@@ -29,11 +29,15 @@ struct {
 private(A) struct bpf_spin_lock lock;
 private(A) struct bpf_rb_root rbtree __contains(foo, node);
 
-__noinline void *exception_cb_bad_ret_type(u64 cookie)
+__noinline void *exception_cb_bad_ret_type1(u64 cookie)
 {
 	return NULL;
 }
 
+__noinline void exception_cb_bad_ret_type2(u64 cookie)
+{
+}
+
 __noinline int exception_cb_bad_arg_0(void)
 {
 	return 0;
@@ -50,8 +54,8 @@ __noinline int exception_cb_ok_arg_small(int a)
 }
 
 SEC("?tc")
-__exception_cb(exception_cb_bad_ret_type)
-__failure __msg("Global function exception_cb_bad_ret_type() doesn't return scalar.")
+__exception_cb(exception_cb_bad_ret_type1)
+__failure __msg("Global function exception_cb_bad_ret_type1() return value not void or scalar.")
 int reject_exception_cb_type_1(struct __sk_buff *ctx)
 {
 	bpf_throw(0);
@@ -85,6 +89,15 @@ int reject_exception_cb_type_4(struct __sk_buff *ctx)
 	return 0;
 }
 
+SEC("?tc")
+__exception_cb(exception_cb_bad_ret_type2)
+__failure __msg("exception cb cannot return void")
+int reject_exception_cb_type_5(struct __sk_buff *ctx)
+{
+	bpf_throw(0);
+	return 0;
+}
+
 __noinline
 static int timer_cb(void *map, int *key, struct bpf_timer *timer)
 {
@@ -346,4 +359,20 @@ int reject_exception_throw_cb_diff(struct __sk_buff *ctx)
 	return 0;
 }
 
+__weak
+void foo(void)
+{
+	bpf_throw(1);
+}
+
+SEC("?fentry/bpf_check")
+__failure __msg("At program exit the register R1 has smin=1 smax=1 should")
+int reject_out_of_range_global_throw(struct __sk_buff *skb)
+{
+	foo();
+
+	return 0;
+}
+
+
 char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/freplace_int_with_void.c b/tools/testing/selftests/bpf/progs/freplace_int_with_void.c
new file mode 100644
index 000000000000..cbb8f8ff2581
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/freplace_int_with_void.c
@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <linux/pkt_cls.h>
+#include <bpf/bpf_helpers.h>
+
+SEC("freplace/global_func2")
+void test_freplace_int_with_void(struct __sk_buff *skb)
+{
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/freplace_void.c b/tools/testing/selftests/bpf/progs/freplace_void.c
new file mode 100644
index 000000000000..68b114f477fe
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/freplace_void.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+SEC("freplace/foo")
+void test_freplace_void(struct __sk_buff *skb)
+{
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/test_global_func7.c b/tools/testing/selftests/bpf/progs/test_global_func7.c
index f182febfde3c..9e59625c1c92 100644
--- a/tools/testing/selftests/bpf/progs/test_global_func7.c
+++ b/tools/testing/selftests/bpf/progs/test_global_func7.c
@@ -12,7 +12,7 @@ void foo(struct __sk_buff *skb)
 }
 
 SEC("tc")
-__failure __msg("foo() doesn't return scalar")
+__success
 int global_func7(struct __sk_buff *skb)
 {
 	foo(skb);
diff --git a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
index 20904cd2baa2..f02012a2fbaa 100644
--- a/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
+++ b/tools/testing/selftests/bpf/progs/verifier_global_subprogs.c
@@ -388,4 +388,23 @@ int arg_tag_dynptr(struct xdp_md *ctx)
 	return subprog_dynptr(&dptr);
 }
 
+__weak
+void foo(void)
+{
+}
+
+SEC("?tc")
+__failure __msg("R0 !read_ok")
+int return_from_void_global(struct __sk_buff *skb)
+{
+	foo();
+
+	asm volatile(
+		"r1 = r0;"
+		:::
+	);
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";