bpf: Use a table to drive helper arg type checks

The mapping between bpf_arg_type and bpf_reg_type is encoded in a big
hairy if statement that is hard to follow. The debug output also leaves
to be desired: if a reg_type doesn't match we only print one of the
options, instead printing all the valid ones.

Convert the if statement into a table which is then used to drive type
checking. If none of the reg_types match we print all options, e.g.:

    R2 type=rdonly_buf expected=fp, pkt, pkt_meta, map_value
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200921121227.255763-12-lmb@cloudflare.com

include/linux/bpf.h

@@ -292,6 +292,7 @@ enum bpf_arg_type {
 	ARG_PTR_TO_ALLOC_MEM,	/* pointer to dynamically allocated memory */
 	ARG_PTR_TO_ALLOC_MEM_OR_NULL,	/* pointer to dynamically allocated memory or NULL */
 	ARG_CONST_ALLOC_SIZE_OR_ZERO,	/* number of allocated bytes requested */
+	__BPF_ARG_TYPE_MAX,
 };
 
 /* type of values returned from helper functions */

kernel/bpf/verifier.c

@@ -3903,12 +3903,6 @@ static bool arg_type_is_mem_size(enum bpf_arg_type type)
 	       type == ARG_CONST_SIZE_OR_ZERO;
 }
 
-static bool arg_type_is_alloc_mem_ptr(enum bpf_arg_type type)
-{
-	return type == ARG_PTR_TO_ALLOC_MEM ||
-	       type == ARG_PTR_TO_ALLOC_MEM_OR_NULL;
-}
-
 static bool arg_type_is_alloc_size(enum bpf_arg_type type)
 {
 	return type == ARG_CONST_ALLOC_SIZE_OR_ZERO;
@@ -3957,14 +3951,115 @@ static int resolve_map_arg_type(struct bpf_verifier_env *env,
 	return 0;
 }
 
+struct bpf_reg_types {
+	const enum bpf_reg_type types[10];
+};
+
+static const struct bpf_reg_types map_key_value_types = {
+	.types = {
+		PTR_TO_STACK,
+		PTR_TO_PACKET,
+		PTR_TO_PACKET_META,
+		PTR_TO_MAP_VALUE,
+	},
+};
+
+static const struct bpf_reg_types sock_types = {
+	.types = {
+		PTR_TO_SOCK_COMMON,
+		PTR_TO_SOCKET,
+		PTR_TO_TCP_SOCK,
+		PTR_TO_XDP_SOCK,
+	},
+};
+
+static const struct bpf_reg_types mem_types = {
+	.types = {
+		PTR_TO_STACK,
+		PTR_TO_PACKET,
+		PTR_TO_PACKET_META,
+		PTR_TO_MAP_VALUE,
+		PTR_TO_MEM,
+		PTR_TO_RDONLY_BUF,
+		PTR_TO_RDWR_BUF,
+	},
+};
+
+static const struct bpf_reg_types int_ptr_types = {
+	.types = {
+		PTR_TO_STACK,
+		PTR_TO_PACKET,
+		PTR_TO_PACKET_META,
+		PTR_TO_MAP_VALUE,
+	},
+};
+
+static const struct bpf_reg_types fullsock_types = { .types = { PTR_TO_SOCKET } };
+static const struct bpf_reg_types scalar_types = { .types = { SCALAR_VALUE } };
+static const struct bpf_reg_types context_types = { .types = { PTR_TO_CTX } };
+static const struct bpf_reg_types alloc_mem_types = { .types = { PTR_TO_MEM } };
+static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_TO_MAP } };
+static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
+static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
+
+static const struct bpf_reg_types *compatible_reg_types[] = {
+	[ARG_PTR_TO_MAP_KEY]		= &map_key_value_types,
+	[ARG_PTR_TO_MAP_VALUE]		= &map_key_value_types,
+	[ARG_PTR_TO_UNINIT_MAP_VALUE]	= &map_key_value_types,
+	[ARG_PTR_TO_MAP_VALUE_OR_NULL]	= &map_key_value_types,
+	[ARG_CONST_SIZE]		= &scalar_types,
+	[ARG_CONST_SIZE_OR_ZERO]	= &scalar_types,
+	[ARG_CONST_ALLOC_SIZE_OR_ZERO]	= &scalar_types,
+	[ARG_CONST_MAP_PTR]		= &const_map_ptr_types,
+	[ARG_PTR_TO_CTX]		= &context_types,
+	[ARG_PTR_TO_CTX_OR_NULL]	= &context_types,
+	[ARG_PTR_TO_SOCK_COMMON]	= &sock_types,
+	[ARG_PTR_TO_SOCKET]		= &fullsock_types,
+	[ARG_PTR_TO_SOCKET_OR_NULL]	= &fullsock_types,
+	[ARG_PTR_TO_BTF_ID]		= &btf_ptr_types,
+	[ARG_PTR_TO_SPIN_LOCK]		= &spin_lock_types,
+	[ARG_PTR_TO_MEM]		= &mem_types,
+	[ARG_PTR_TO_MEM_OR_NULL]	= &mem_types,
+	[ARG_PTR_TO_UNINIT_MEM]		= &mem_types,
+	[ARG_PTR_TO_ALLOC_MEM]		= &alloc_mem_types,
+	[ARG_PTR_TO_ALLOC_MEM_OR_NULL]	= &alloc_mem_types,
+	[ARG_PTR_TO_INT]		= &int_ptr_types,
+	[ARG_PTR_TO_LONG]		= &int_ptr_types,
+	[__BPF_ARG_TYPE_MAX]		= NULL,
+};
+
+static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
+			  const struct bpf_reg_types *compatible)
+{
+	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+	enum bpf_reg_type expected, type = reg->type;
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(compatible->types); i++) {
+		expected = compatible->types[i];
+		if (expected == NOT_INIT)
+			break;
+
+		if (type == expected)
+			return 0;
+	}
+
+	verbose(env, "R%d type=%s expected=", regno, reg_type_str[type]);
+	for (j = 0; j + 1 < i; j++)
+		verbose(env, "%s, ", reg_type_str[compatible->types[j]]);
+	verbose(env, "%s\n", reg_type_str[compatible->types[j]]);
+	return -EACCES;
+}
+
 static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			  struct bpf_call_arg_meta *meta,
 			  const struct bpf_func_proto *fn)
 {
 	u32 regno = BPF_REG_1 + arg;
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
-	enum bpf_reg_type expected_type, type = reg->type;
 	enum bpf_arg_type arg_type = fn->arg_type[arg];
+	const struct bpf_reg_types *compatible;
+	enum bpf_reg_type type = reg->type;
 	int err = 0;
 
 	if (arg_type == ARG_DONTCARE)
@@ -4003,72 +4098,16 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		 */
 		goto skip_type_check;
 
-	if (arg_type == ARG_PTR_TO_MAP_KEY ||
-	    arg_type == ARG_PTR_TO_MAP_VALUE ||
-	    arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE ||
-	    arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL) {
-		expected_type = PTR_TO_STACK;
-		if (!type_is_pkt_pointer(type) &&
-		    type != PTR_TO_MAP_VALUE &&
-		    type != expected_type)
-			goto err_type;
-	} else if (arg_type == ARG_CONST_SIZE ||
-		   arg_type == ARG_CONST_SIZE_OR_ZERO ||
-		   arg_type == ARG_CONST_ALLOC_SIZE_OR_ZERO) {
-		expected_type = SCALAR_VALUE;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type == ARG_CONST_MAP_PTR) {
-		expected_type = CONST_PTR_TO_MAP;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type == ARG_PTR_TO_CTX ||
-		   arg_type == ARG_PTR_TO_CTX_OR_NULL) {
-		expected_type = PTR_TO_CTX;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type == ARG_PTR_TO_SOCK_COMMON) {
-		expected_type = PTR_TO_SOCK_COMMON;
-		/* Any sk pointer can be ARG_PTR_TO_SOCK_COMMON */
-		if (!type_is_sk_pointer(type))
-			goto err_type;
-	} else if (arg_type == ARG_PTR_TO_SOCKET ||
-		   arg_type == ARG_PTR_TO_SOCKET_OR_NULL) {
-		expected_type = PTR_TO_SOCKET;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type == ARG_PTR_TO_BTF_ID) {
-		expected_type = PTR_TO_BTF_ID;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
-		expected_type = PTR_TO_MAP_VALUE;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type_is_mem_ptr(arg_type)) {
-		expected_type = PTR_TO_STACK;
-		if (!type_is_pkt_pointer(type) &&
-		    type != PTR_TO_MAP_VALUE &&
-		    type != PTR_TO_MEM &&
-		    type != PTR_TO_RDONLY_BUF &&
-		    type != PTR_TO_RDWR_BUF &&
-		    type != expected_type)
-			goto err_type;
-	} else if (arg_type_is_alloc_mem_ptr(arg_type)) {
-		expected_type = PTR_TO_MEM;
-		if (type != expected_type)
-			goto err_type;
-	} else if (arg_type_is_int_ptr(arg_type)) {
-		expected_type = PTR_TO_STACK;
-		if (!type_is_pkt_pointer(type) &&
-		    type != PTR_TO_MAP_VALUE &&
-		    type != expected_type)
-			goto err_type;
-	} else {
-		verbose(env, "unsupported arg_type %d\n", arg_type);
+	compatible = compatible_reg_types[arg_type];
+	if (!compatible) {
+		verbose(env, "verifier internal error: unsupported arg type %d\n", arg_type);
 		return -EFAULT;
 	}
 
+	err = check_reg_type(env, regno, compatible);
+	if (err)
+		return err;
+
 	if (type == PTR_TO_BTF_ID) {
 		const u32 *btf_id = fn->arg_btf_id[arg];
 
@@ -4221,10 +4260,6 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 	}
 
 	return err;
-err_type:
-	verbose(env, "R%d type=%s expected=%s\n", regno,
-		reg_type_str[type], reg_type_str[expected_type]);
-	return -EACCES;
 }
 
 static bool may_update_sockmap(struct bpf_verifier_env *env, int func_id)