include/linux/bpf_verifier.h

   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 */