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 (1ULL << 31)
  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 INT_MAX
  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         /* This field must be last, for states_equal() reasons. */
  80         enum bpf_reg_liveness live;
  81 };
  82
  83 enum bpf_stack_slot_type {
  84         STACK_INVALID,    /* nothing was stored in this stack slot */
  85         STACK_SPILL,      /* register spilled into stack */
  86         STACK_MISC        /* BPF program wrote some data into this slot */
  87 };
  88
  89 #define BPF_REG_SIZE 8  /* size of eBPF register in bytes */
  90
  91 /* state of the program:
  92  * type of all registers and stack info
  93  */
  94 struct bpf_verifier_state {
  95         struct bpf_reg_state regs[MAX_BPF_REG];
  96         u8 stack_slot_type[MAX_BPF_STACK];
  97         struct bpf_reg_state spilled_regs[MAX_BPF_STACK / BPF_REG_SIZE];
  98         struct bpf_verifier_state *parent;
  99 };
 100
 101 /* linked list of verifier states used to prune search */
 102 struct bpf_verifier_state_list {
 103         struct bpf_verifier_state state;
 104         struct bpf_verifier_state_list *next;
 105 };
 106
 107 struct bpf_insn_aux_data {
 108         union {
 109                 enum bpf_reg_type ptr_type;     /* pointer type for load/store insns */
 110                 struct bpf_map *map_ptr;        /* pointer for call insn into lookup_elem */
 111         };
 112         int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
 113         int converted_op_size; /* the valid value width after perceived conversion */
 114 };
 115
 116 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
 117
 118 struct bpf_verifier_env;
 119 struct bpf_ext_analyzer_ops {
 120         int (*insn_hook)(struct bpf_verifier_env *env,
 121                          int insn_idx, int prev_insn_idx);
 122 };
 123
 124 /* single container for all structs
 125  * one verifier_env per bpf_check() call
 126  */
 127 struct bpf_verifier_env {
 128         struct bpf_prog *prog;          /* eBPF program being verified */
 129         struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
 130         int stack_size;                 /* number of states to be processed */
 131         bool strict_alignment;          /* perform strict pointer alignment checks */
 132         struct bpf_verifier_state cur_state; /* current verifier state */
 133         struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
 134         const struct bpf_ext_analyzer_ops *analyzer_ops; /* external analyzer ops */
 135         void *analyzer_priv; /* pointer to external analyzer's private data */
 136         struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
 137         u32 used_map_cnt;               /* number of used maps */
 138         u32 id_gen;                     /* used to generate unique reg IDs */
 139         bool allow_ptr_leaks;
 140         bool seen_direct_write;
 141         struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
 142 };
 143
 144 int bpf_analyzer(struct bpf_prog *prog, const struct bpf_ext_analyzer_ops *ops,
 145                  void *priv);
 146
 147 #endif /* _LINUX_BPF_VERIFIER_H */