bpf: Factor out program return value calculation

Factor the return value range calculation logic in check_return_code
out of the function in preparation for separating the return value
validation logic for BPF_EXIT and bpf_throw().

No functional changes. The change made in return_retval_code's handling
of PROG_TRACING program types (not error'ing on the default case) is a
no-op because the match on the program attach type is exhaustive.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260228184759.108145-2-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 125 insertions, 101 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 34f89ed29c47..89e6d2f6bdf6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2953,7 +2953,11 @@ 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)
@@ -11175,10 +11179,9 @@ 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 +11225,7 @@ 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;
@@ -17841,6 +17844,115 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	return 0;
 }
 
+
+static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_range *range)
+{
+	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
+
+	/* Default return value range. */
+	*range = retval_range(0, 1);
+
+	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;
+		}
+		break;
+	case BPF_PROG_TYPE_CGROUP_SKB:
+		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:
+	case BPF_PROG_TYPE_CGROUP_DEVICE:
+	case BPF_PROG_TYPE_CGROUP_SYSCTL:
+	case BPF_PROG_TYPE_CGROUP_SOCKOPT:
+		break;
+	case BPF_PROG_TYPE_RAW_TRACEPOINT:
+		if (!env->prog->aux->attach_btf_id)
+			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);
+			break;
+		case BPF_TRACE_RAW_TP:
+		case BPF_MODIFY_RETURN:
+			return false;
+		case BPF_TRACE_ITER:
+		default:
+			break;
+		}
+		break;
+	case BPF_PROG_TYPE_KPROBE:
+		switch (env->prog->expected_attach_type) {
+		case BPF_TRACE_KPROBE_SESSION:
+		case BPF_TRACE_UPROBE_SESSION:
+			break;
+		default:
+			return false;
+		}
+		break;
+	case BPF_PROG_TYPE_SK_LOOKUP:
+		*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 false;
+			/* no restricted range, any return value is allowed */
+			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);
+		}
+		break;
+
+	case BPF_PROG_TYPE_NETFILTER:
+		*range = retval_range(NF_DROP, NF_ACCEPT);
+		break;
+	case BPF_PROG_TYPE_STRUCT_OPS:
+		*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 int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
 {
 	const char *exit_ctx = "At program exit";
@@ -17849,18 +17961,17 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
 	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;
+	int err;
 
 	/* 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. */
+				/* See return_retval_range, can be 0 or 0-1 depending on hook. */
 				break;
 			if (!prog->aux->attach_func_proto->type)
 				return 0;
@@ -17918,101 +18029,14 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
 		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);
-		}
-		break;
-	case BPF_PROG_TYPE_CGROUP_SOCK:
-	case BPF_PROG_TYPE_SOCK_OPS:
-	case BPF_PROG_TYPE_CGROUP_DEVICE:
-	case BPF_PROG_TYPE_CGROUP_SYSCTL:
-	case BPF_PROG_TYPE_CGROUP_SOCKOPT:
-		break;
-	case BPF_PROG_TYPE_RAW_TRACEPOINT:
-		if (!env->prog->aux->attach_btf_id)
-			return 0;
-		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);
-			break;
-		case BPF_TRACE_RAW_TP:
-		case BPF_MODIFY_RETURN:
-			return 0;
-		case BPF_TRACE_ITER:
-			break;
-		default:
-			return -ENOTSUPP;
-		}
-		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;
-		}
-		break;
-	case BPF_PROG_TYPE_SK_LOOKUP:
-		range = retval_range(SK_DROP, SK_PASS);
-		break;
+	if (prog_type == BPF_PROG_TYPE_STRUCT_OPS && !ret_type)
+		return 0;
 
-	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;
-			/* no restricted range, any return value is allowed */
-			if (range.minval == S32_MIN && range.maxval == S32_MAX)
-				return 0;
-			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);
-		}
-		break;
+	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);
 
-	case BPF_PROG_TYPE_NETFILTER:
-		range = retval_range(NF_DROP, NF_ACCEPT);
-		break;
-	case BPF_PROG_TYPE_STRUCT_OPS:
-		if (!ret_type)
-			return 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:
+	if (!return_retval_range(env, &range))
 		return 0;
-	}
 
 enforce_retval:
 	if (reg->type != SCALAR_VALUE) {
@@ -18025,7 +18049,7 @@ 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 &&