xref: /openbmc/linux/include/linux/bpf_verifier.h (revision 160b8e75)
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 	/* Fixed part of pointer offset, pointer types only */
55 	s32 off;
56 	/* For PTR_TO_PACKET, used to find other pointers with the same variable
57 	 * offset, so they can share range knowledge.
58 	 * For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
59 	 * came from, when one is tested for != NULL.
60 	 */
61 	u32 id;
62 	/* Ordering of fields matters.  See states_equal() */
63 	/* For scalar types (SCALAR_VALUE), this represents our knowledge of
64 	 * the actual value.
65 	 * For pointer types, this represents the variable part of the offset
66 	 * from the pointed-to object, and is shared with all bpf_reg_states
67 	 * with the same id as us.
68 	 */
69 	struct tnum var_off;
70 	/* Used to determine if any memory access using this register will
71 	 * result in a bad access.
72 	 * These refer to the same value as var_off, not necessarily the actual
73 	 * contents of the register.
74 	 */
75 	s64 smin_value; /* minimum possible (s64)value */
76 	s64 smax_value; /* maximum possible (s64)value */
77 	u64 umin_value; /* minimum possible (u64)value */
78 	u64 umax_value; /* maximum possible (u64)value */
79 	/* Inside the callee two registers can be both PTR_TO_STACK like
80 	 * R1=fp-8 and R2=fp-8, but one of them points to this function stack
81 	 * while another to the caller's stack. To differentiate them 'frameno'
82 	 * is used which is an index in bpf_verifier_state->frame[] array
83 	 * pointing to bpf_func_state.
84 	 * This field must be second to last, for states_equal() reasons.
85 	 */
86 	u32 frameno;
87 	/* This field must be last, for states_equal() reasons. */
88 	enum bpf_reg_liveness live;
89 };
90 
91 enum bpf_stack_slot_type {
92 	STACK_INVALID,    /* nothing was stored in this stack slot */
93 	STACK_SPILL,      /* register spilled into stack */
94 	STACK_MISC,	  /* BPF program wrote some data into this slot */
95 	STACK_ZERO,	  /* BPF program wrote constant zero */
96 };
97 
98 #define BPF_REG_SIZE 8	/* size of eBPF register in bytes */
99 
100 struct bpf_stack_state {
101 	struct bpf_reg_state spilled_ptr;
102 	u8 slot_type[BPF_REG_SIZE];
103 };
104 
105 /* state of the program:
106  * type of all registers and stack info
107  */
108 struct bpf_func_state {
109 	struct bpf_reg_state regs[MAX_BPF_REG];
110 	struct bpf_verifier_state *parent;
111 	/* index of call instruction that called into this func */
112 	int callsite;
113 	/* stack frame number of this function state from pov of
114 	 * enclosing bpf_verifier_state.
115 	 * 0 = main function, 1 = first callee.
116 	 */
117 	u32 frameno;
118 	/* subprog number == index within subprog_stack_depth
119 	 * zero == main subprog
120 	 */
121 	u32 subprogno;
122 
123 	/* should be second to last. See copy_func_state() */
124 	int allocated_stack;
125 	struct bpf_stack_state *stack;
126 };
127 
128 #define MAX_CALL_FRAMES 8
129 struct bpf_verifier_state {
130 	/* call stack tracking */
131 	struct bpf_func_state *frame[MAX_CALL_FRAMES];
132 	struct bpf_verifier_state *parent;
133 	u32 curframe;
134 };
135 
136 /* linked list of verifier states used to prune search */
137 struct bpf_verifier_state_list {
138 	struct bpf_verifier_state state;
139 	struct bpf_verifier_state_list *next;
140 };
141 
142 struct bpf_insn_aux_data {
143 	union {
144 		enum bpf_reg_type ptr_type;	/* pointer type for load/store insns */
145 		struct bpf_map *map_ptr;	/* pointer for call insn into lookup_elem */
146 		s32 call_imm;			/* saved imm field of call insn */
147 	};
148 	int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
149 	bool seen; /* this insn was processed by the verifier */
150 };
151 
152 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
153 
154 #define BPF_VERIFIER_TMP_LOG_SIZE	1024
155 
156 struct bpf_verifer_log {
157 	u32 level;
158 	char kbuf[BPF_VERIFIER_TMP_LOG_SIZE];
159 	char __user *ubuf;
160 	u32 len_used;
161 	u32 len_total;
162 };
163 
164 static inline bool bpf_verifier_log_full(const struct bpf_verifer_log *log)
165 {
166 	return log->len_used >= log->len_total - 1;
167 }
168 
169 #define BPF_MAX_SUBPROGS 256
170 
171 /* single container for all structs
172  * one verifier_env per bpf_check() call
173  */
174 struct bpf_verifier_env {
175 	struct bpf_prog *prog;		/* eBPF program being verified */
176 	const struct bpf_verifier_ops *ops;
177 	struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
178 	int stack_size;			/* number of states to be processed */
179 	bool strict_alignment;		/* perform strict pointer alignment checks */
180 	struct bpf_verifier_state *cur_state; /* current verifier state */
181 	struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
182 	struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
183 	u32 used_map_cnt;		/* number of used maps */
184 	u32 id_gen;			/* used to generate unique reg IDs */
185 	bool allow_ptr_leaks;
186 	bool seen_direct_write;
187 	struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
188 	struct bpf_verifer_log log;
189 	u32 subprog_starts[BPF_MAX_SUBPROGS];
190 	/* computes the stack depth of each bpf function */
191 	u16 subprog_stack_depth[BPF_MAX_SUBPROGS + 1];
192 	u32 subprog_cnt;
193 };
194 
195 __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
196 					   const char *fmt, ...);
197 
198 static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
199 {
200 	struct bpf_verifier_state *cur = env->cur_state;
201 
202 	return cur->frame[cur->curframe]->regs;
203 }
204 
205 int bpf_prog_offload_verifier_prep(struct bpf_verifier_env *env);
206 int bpf_prog_offload_verify_insn(struct bpf_verifier_env *env,
207 				 int insn_idx, int prev_insn_idx);
208 
209 #endif /* _LINUX_BPF_VERIFIER_H */
210