1 /* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 */
7 #ifndef _LINUX_BPF_VERIFIER_H
8 #define _LINUX_BPF_VERIFIER_H 1
9
10 #include <linux/bpf.h> /* for enum bpf_reg_type */
11 #include <linux/filter.h> /* for MAX_BPF_STACK */
12 #include <linux/tnum.h>
13
14 /* Maximum variable offset umax_value permitted when resolving memory accesses.
15 * In practice this is far bigger than any realistic pointer offset; this limit
16 * ensures that umax_value + (int)off + (int)size cannot overflow a u64.
17 */
18 #define BPF_MAX_VAR_OFF (1 << 29)
19 /* Maximum variable size permitted for ARG_CONST_SIZE[_OR_ZERO]. This ensures
20 * that converting umax_value to int cannot overflow.
21 */
22 #define BPF_MAX_VAR_SIZ (1 << 29)
23
24 /* Liveness marks, used for registers and spilled-regs (in stack slots).
25 * Read marks propagate upwards until they find a write mark; they record that
26 * "one of this state's descendants read this reg" (and therefore the reg is
27 * relevant for states_equal() checks).
28 * Write marks collect downwards and do not propagate; they record that "the
29 * straight-line code that reached this state (from its parent) wrote this reg"
30 * (and therefore that reads propagated from this state or its descendants
31 * should not propagate to its parent).
32 * A state with a write mark can receive read marks; it just won't propagate
33 * them to its parent, since the write mark is a property, not of the state,
34 * but of the link between it and its parent. See mark_reg_read() and
35 * mark_stack_slot_read() in kernel/bpf/verifier.c.
36 */
37 enum bpf_reg_liveness {
38 REG_LIVE_NONE = 0, /* reg hasn't been read or written this branch */
39 REG_LIVE_READ, /* reg was read, so we're sensitive to initial value */
40 REG_LIVE_WRITTEN, /* reg was written first, screening off later reads */
41 };
42
43 struct bpf_reg_state {
44 enum bpf_reg_type type;
45 union {
46 /* valid when type == PTR_TO_PACKET */
47 u16 range;
48
49 /* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
50 * PTR_TO_MAP_VALUE_OR_NULL
51 */
52 struct bpf_map *map_ptr;
53
54 /* Max size from any of the above. */
55 unsigned long raw;
56 };
57 /* Fixed part of pointer offset, pointer types only */
58 s32 off;
59 /* For PTR_TO_PACKET, used to find other pointers with the same variable
60 * offset, so they can share range knowledge.
61 * For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
62 * came from, when one is tested for != NULL.
63 */
64 u32 id;
65 /* Ordering of fields matters. See states_equal() */
66 /* For scalar types (SCALAR_VALUE), this represents our knowledge of
67 * the actual value.
68 * For pointer types, this represents the variable part of the offset
69 * from the pointed-to object, and is shared with all bpf_reg_states
70 * with the same id as us.
71 */
72 struct tnum var_off;
73 /* Used to determine if any memory access using this register will
74 * result in a bad access.
75 * These refer to the same value as var_off, not necessarily the actual
76 * contents of the register.
77 */
78 s64 smin_value; /* minimum possible (s64)value */
79 s64 smax_value; /* maximum possible (s64)value */
80 u64 umin_value; /* minimum possible (u64)value */
81 u64 umax_value; /* maximum possible (u64)value */
82 /* This field must be last, for states_equal() reasons. */
83 enum bpf_reg_liveness live;
84 };
85
86 enum bpf_stack_slot_type {
87 STACK_INVALID, /* nothing was stored in this stack slot */
88 STACK_SPILL, /* register spilled into stack */
89 STACK_MISC /* BPF program wrote some data into this slot */
90 };
91
92 #define BPF_REG_SIZE 8 /* size of eBPF register in bytes */
93
94 struct bpf_stack_state {
95 struct bpf_reg_state spilled_ptr;
96 u8 slot_type[BPF_REG_SIZE];
97 };
98
99 /* state of the program:
100 * type of all registers and stack info
101 */
102 struct bpf_verifier_state {
103 struct bpf_reg_state regs[MAX_BPF_REG];
104 struct bpf_verifier_state *parent;
105 int allocated_stack;
106 struct bpf_stack_state *stack;
107 bool speculative;
108 };
109
110 /* linked list of verifier states used to prune search */
111 struct bpf_verifier_state_list {
112 struct bpf_verifier_state state;
113 struct bpf_verifier_state_list *next;
114 };
115
116 /* Possible states for alu_state member. */
117 #define BPF_ALU_SANITIZE_SRC 1U
118 #define BPF_ALU_SANITIZE_DST 2U
119 #define BPF_ALU_NEG_VALUE (1U << 2)
120 #define BPF_ALU_NON_POINTER (1U << 3)
121 #define BPF_ALU_SANITIZE (BPF_ALU_SANITIZE_SRC | \
122 BPF_ALU_SANITIZE_DST)
123
124 struct bpf_insn_aux_data {
125 union {
126 enum bpf_reg_type ptr_type; /* pointer type for load/store insns */
127 struct bpf_map *map_ptr; /* pointer for call insn into lookup_elem */
128 u32 alu_limit; /* limit for add/sub register with pointer */
129 };
130 int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
131 int sanitize_stack_off; /* stack slot to be cleared */
132 bool seen; /* this insn was processed by the verifier */
133 u8 alu_state; /* used in combination with alu_limit */
134 };
135
136 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
137
138 struct bpf_verifier_env;
139 struct bpf_ext_analyzer_ops {
140 int (*insn_hook)(struct bpf_verifier_env *env,
141 int insn_idx, int prev_insn_idx);
142 };
143
144 /* single container for all structs
145 * one verifier_env per bpf_check() call
146 */
147 struct bpf_verifier_env {
148 u32 insn_idx;
149 u32 prev_insn_idx;
150 struct bpf_prog *prog; /* eBPF program being verified */
151 struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
152 int stack_size; /* number of states to be processed */
153 bool strict_alignment; /* perform strict pointer alignment checks */
154 struct bpf_verifier_state *cur_state; /* current verifier state */
155 struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
156 const struct bpf_ext_analyzer_ops *analyzer_ops; /* external analyzer ops */
157 void *analyzer_priv; /* pointer to external analyzer's private data */
158 struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
159 u32 used_map_cnt; /* number of used maps */
160 u32 id_gen; /* used to generate unique reg IDs */
161 bool allow_ptr_leaks;
162 bool seen_direct_write;
163 struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
164 };
165
cur_regs(struct bpf_verifier_env * env)166 static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
167 {
168 return env->cur_state->regs;
169 }
170
171 int bpf_analyzer(struct bpf_prog *prog, const struct bpf_ext_analyzer_ops *ops,
172 void *priv);
173
174 #endif /* _LINUX_BPF_VERIFIER_H */
175