bpf: Replace ARG_XXX_OR_NULL with ARG_XXX | PTR_MAYBE_NULL

jira VULN-136
cve-pre CVE-2022-0500
commit-author Hao Luo <[email protected]>
commit 48946bd

We have introduced a new type to make bpf_arg composable, by
reserving high bits of bpf_arg to represent flags of a type.

One of the flags is PTR_MAYBE_NULL which indicates a pointer
may be NULL. When applying this flag to an arg_type, it means
the arg can take NULL pointer. This patch switches the
qualified arg_types to use this flag. The arg_types changed
in this patch include:

1. ARG_PTR_TO_MAP_VALUE_OR_NULL
2. ARG_PTR_TO_MEM_OR_NULL
3. ARG_PTR_TO_CTX_OR_NULL
4. ARG_PTR_TO_SOCKET_OR_NULL
5. ARG_PTR_TO_ALLOC_MEM_OR_NULL
6. ARG_PTR_TO_STACK_OR_NULL

This patch does not eliminate the use of these arg_types, instead
it makes them an alias to the 'ARG_XXX | PTR_MAYBE_NULL'.

	Signed-off-by: Hao Luo <[email protected]>
	Signed-off-by: Alexei Starovoitov <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
(cherry picked from commit 48946bd)
	Signed-off-by: Brett Mastbergen <[email protected]>

Author: bmastbergen

include/linux/bpf.h

@@ -313,13 +313,11 @@ enum bpf_arg_type {
 	ARG_PTR_TO_MAP_KEY,	/* pointer to stack used as map key */
 	ARG_PTR_TO_MAP_VALUE,	/* pointer to stack used as map value */
 	ARG_PTR_TO_UNINIT_MAP_VALUE,	/* pointer to valid memory used to store a map value */
-	ARG_PTR_TO_MAP_VALUE_OR_NULL,	/* pointer to stack used as map value or NULL */
 
 	/* the following constraints used to prototype bpf_memcmp() and other
 	 * functions that access data on eBPF program stack
 	 */
 	ARG_PTR_TO_MEM,		/* pointer to valid memory (stack, packet, map value) */
-	ARG_PTR_TO_MEM_OR_NULL, /* pointer to valid memory or NULL */
 	ARG_PTR_TO_UNINIT_MEM,	/* pointer to memory does not need to be initialized,
 				 * helper function must fill all bytes or clear
 				 * them in error case.
@@ -329,25 +327,30 @@ enum bpf_arg_type {
 	ARG_CONST_SIZE_OR_ZERO,	/* number of bytes accessed from memory or 0 */
 
 	ARG_PTR_TO_CTX,		/* pointer to context */
-	ARG_PTR_TO_CTX_OR_NULL,	/* pointer to context or NULL */
 	ARG_ANYTHING,		/* any (initialized) argument is ok */
 	ARG_PTR_TO_SPIN_LOCK,	/* pointer to bpf_spin_lock */
 	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
 	ARG_PTR_TO_INT,		/* pointer to int */
 	ARG_PTR_TO_LONG,	/* pointer to long */
 	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */
-	ARG_PTR_TO_SOCKET_OR_NULL,	/* pointer to bpf_sock (fullsock) or NULL */
 	ARG_PTR_TO_BTF_ID,	/* pointer to in-kernel struct */
 	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 */
 	ARG_PTR_TO_BTF_ID_SOCK_COMMON,	/* pointer to in-kernel sock_common or bpf-mirrored bpf_sock */
 	ARG_PTR_TO_PERCPU_BTF_ID,	/* pointer to in-kernel percpu type */
 	ARG_PTR_TO_FUNC,	/* pointer to a bpf program function */
-	ARG_PTR_TO_STACK_OR_NULL,	/* pointer to stack or NULL */
+	ARG_PTR_TO_STACK,	/* pointer to stack */
 	ARG_PTR_TO_CONST_STR,	/* pointer to a null terminated read-only string */
 	__BPF_ARG_TYPE_MAX,
 
+	/* Extended arg_types. */
+	ARG_PTR_TO_MAP_VALUE_OR_NULL	= PTR_MAYBE_NULL | ARG_PTR_TO_MAP_VALUE,
+	ARG_PTR_TO_MEM_OR_NULL		= PTR_MAYBE_NULL | ARG_PTR_TO_MEM,
+	ARG_PTR_TO_CTX_OR_NULL		= PTR_MAYBE_NULL | ARG_PTR_TO_CTX,
+	ARG_PTR_TO_SOCKET_OR_NULL	= PTR_MAYBE_NULL | ARG_PTR_TO_SOCKET,
+	ARG_PTR_TO_ALLOC_MEM_OR_NULL	= PTR_MAYBE_NULL | ARG_PTR_TO_ALLOC_MEM,
+	ARG_PTR_TO_STACK_OR_NULL	= PTR_MAYBE_NULL | ARG_PTR_TO_STACK,
+
 	/* This must be the last entry. Its purpose is to ensure the enum is
 	 * wide enough to hold the higher bits reserved for bpf_type_flag.
 	 */

kernel/bpf/verifier.c

@@ -479,14 +479,9 @@ static bool arg_type_may_be_refcounted(enum bpf_arg_type type)
 	return type == ARG_PTR_TO_SOCK_COMMON;
 }
 
-static bool arg_type_may_be_null(enum bpf_arg_type type)
+static bool type_may_be_null(u32 type)
 {
-	return type == ARG_PTR_TO_MAP_VALUE_OR_NULL ||
-	       type == ARG_PTR_TO_MEM_OR_NULL ||
-	       type == ARG_PTR_TO_CTX_OR_NULL ||
-	       type == ARG_PTR_TO_SOCKET_OR_NULL ||
-	       type == ARG_PTR_TO_ALLOC_MEM_OR_NULL ||
-	       type == ARG_PTR_TO_STACK_OR_NULL;
+	return type & PTR_MAYBE_NULL;
 }
 
 /* Determine whether the function releases some resources allocated by another
@@ -4647,9 +4642,8 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 
 static bool arg_type_is_mem_ptr(enum bpf_arg_type type)
 {
-	return type == ARG_PTR_TO_MEM ||
-	       type == ARG_PTR_TO_MEM_OR_NULL ||
-	       type == ARG_PTR_TO_UNINIT_MEM;
+	return base_type(type) == ARG_PTR_TO_MEM ||
+	       base_type(type) == ARG_PTR_TO_UNINIT_MEM;
 }
 
 static bool arg_type_is_mem_size(enum bpf_arg_type type)
@@ -4782,31 +4776,26 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 	[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,
 #ifdef CONFIG_NET
 	[ARG_PTR_TO_BTF_ID_SOCK_COMMON]	= &btf_id_sock_common_types,
 #endif
 	[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,
 	[ARG_PTR_TO_PERCPU_BTF_ID]	= &percpu_btf_ptr_types,
 	[ARG_PTR_TO_FUNC]		= &func_ptr_types,
-	[ARG_PTR_TO_STACK_OR_NULL]	= &stack_ptr_types,
+	[ARG_PTR_TO_STACK]		= &stack_ptr_types,
 	[ARG_PTR_TO_CONST_STR]		= &const_str_ptr_types,
 };
 
@@ -4819,7 +4808,7 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	const struct bpf_reg_types *compatible;
 	int i, j;
 
-	compatible = compatible_reg_types[arg_type];
+	compatible = compatible_reg_types[base_type(arg_type)];
 	if (!compatible) {
 		verbose(env, "verifier internal error: unsupported arg type %d\n", arg_type);
 		return -EFAULT;
@@ -4900,15 +4889,14 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		return -EACCES;
 	}
 
-	if (arg_type == ARG_PTR_TO_MAP_VALUE ||
-	    arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE ||
-	    arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL) {
+	if (base_type(arg_type) == ARG_PTR_TO_MAP_VALUE ||
+	    base_type(arg_type) == ARG_PTR_TO_UNINIT_MAP_VALUE) {
 		err = resolve_map_arg_type(env, meta, &arg_type);
 		if (err)
 			return err;
 	}
 
-	if (register_is_null(reg) && arg_type_may_be_null(arg_type))
+	if (register_is_null(reg) && type_may_be_null(arg_type))
 		/* A NULL register has a SCALAR_VALUE type, so skip
 		 * type checking.
 		 */
@@ -4955,10 +4943,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		err = check_helper_mem_access(env, regno,
 					      meta->map_ptr->key_size, false,
 					      NULL);
-	} else if (arg_type == ARG_PTR_TO_MAP_VALUE ||
-		   (arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL &&
-		    !register_is_null(reg)) ||
-		   arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE) {
+	} else if (base_type(arg_type) == ARG_PTR_TO_MAP_VALUE ||
+		   base_type(arg_type) == ARG_PTR_TO_UNINIT_MAP_VALUE) {
+		if (type_may_be_null(arg_type) && register_is_null(reg))
+			return 0;
+
 		/* bpf_map_xxx(..., map_ptr, ..., value) call:
 		 * check [value, value + map->value_size) validity
 		 */