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         REG_LIVE_DONE = 4, /* liveness won't be updating this register anymore */
  42 };
  43
  44 struct bpf_reg_state {
  45         /* Ordering of fields matters.  See states_equal() */
  46         enum bpf_reg_type type;
  47         union {
  48                 /* valid when type == PTR_TO_PACKET */
  49                 u16 range;
  50
  51                 /* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
  52                  *   PTR_TO_MAP_VALUE_OR_NULL
  53                  */
  54                 struct bpf_map *map_ptr;
  55
  56                 /* Max size from any of the above. */
  57                 unsigned long raw;
  58         };
  59         /* Fixed part of pointer offset, pointer types only */
  60         s32 off;
  61         /* For PTR_TO_PACKET, used to find other pointers with the same variable
  62          * offset, so they can share range knowledge.
  63          * For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
  64          * came from, when one is tested for != NULL.
  65          * For PTR_TO_SOCKET this is used to share which pointers retain the
  66          * same reference to the socket, to determine proper reference freeing.
  67          */
  68         u32 id;
  69         /* For scalar types (SCALAR_VALUE), this represents our knowledge of
  70          * the actual value.
  71          * For pointer types, this represents the variable part of the offset
  72          * from the pointed-to object, and is shared with all bpf_reg_states
  73          * with the same id as us.
  74          */
  75         struct tnum var_off;
  76         /* Used to determine if any memory access using this register will
  77          * result in a bad access.
  78          * These refer to the same value as var_off, not necessarily the actual
  79          * contents of the register.
  80          */
  81         s64 smin_value; /* minimum possible (s64)value */
  82         s64 smax_value; /* maximum possible (s64)value */
  83         u64 umin_value; /* minimum possible (u64)value */
  84         u64 umax_value; /* maximum possible (u64)value */
  85         /* parentage chain for liveness checking */
  86         struct bpf_reg_state *parent;
  87         /* Inside the callee two registers can be both PTR_TO_STACK like
  88          * R1=fp-8 and R2=fp-8, but one of them points to this function stack
  89          * while another to the caller's stack. To differentiate them 'frameno'
  90          * is used which is an index in bpf_verifier_state->frame[] array
  91          * pointing to bpf_func_state.
  92          */
  93         u32 frameno;
  94         enum bpf_reg_liveness live;
  95 };
  96
  97 enum bpf_stack_slot_type {
  98         STACK_INVALID,    /* nothing was stored in this stack slot */
  99         STACK_SPILL,      /* register spilled into stack */
 100         STACK_MISC,       /* BPF program wrote some data into this slot */
 101         STACK_ZERO,       /* BPF program wrote constant zero */
 102 };
 103
 104 #define BPF_REG_SIZE 8  /* size of eBPF register in bytes */
 105
 106 struct bpf_stack_state {
 107         struct bpf_reg_state spilled_ptr;
 108         u8 slot_type[BPF_REG_SIZE];
 109 };
 110
 111 struct bpf_reference_state {
 112         /* Track each reference created with a unique id, even if the same
 113          * instruction creates the reference multiple times (eg, via CALL).
 114          */
 115         int id;
 116         /* Instruction where the allocation of this reference occurred. This
 117          * is used purely to inform the user of a reference leak.
 118          */
 119         int insn_idx;
 120 };
 121
 122 /* state of the program:
 123  * type of all registers and stack info
 124  */
 125 struct bpf_func_state {
 126         struct bpf_reg_state regs[MAX_BPF_REG];
 127         /* index of call instruction that called into this func */
 128         int callsite;
 129         /* stack frame number of this function state from pov of
 130          * enclosing bpf_verifier_state.
 131          * 0 = main function, 1 = first callee.
 132          */
 133         u32 frameno;
 134         /* subprog number == index within subprog_stack_depth
 135          * zero == main subprog
 136          */
 137         u32 subprogno;
 138
 139         /* The following fields should be last. See copy_func_state() */
 140         int acquired_refs;
 141         struct bpf_reference_state *refs;
 142         int allocated_stack;
 143         struct bpf_stack_state *stack;
 144 };
 145
 146 #define MAX_CALL_FRAMES 8
 147 struct bpf_verifier_state {
 148         /* call stack tracking */
 149         struct bpf_func_state *frame[MAX_CALL_FRAMES];
 150         u32 curframe;
 151         bool speculative;
 152 };
 153
 154 #define bpf_get_spilled_reg(slot, frame)                                \
 155         (((slot < frame->allocated_stack / BPF_REG_SIZE) &&             \
 156           (frame->stack[slot].slot_type[0] == STACK_SPILL))             \
 157          ? &frame->stack[slot].spilled_ptr : NULL)
 158
 159 /* Iterate over 'frame', setting 'reg' to either NULL or a spilled register. */
 160 #define bpf_for_each_spilled_reg(iter, frame, reg)                      \
 161         for (iter = 0, reg = bpf_get_spilled_reg(iter, frame);          \
 162              iter < frame->allocated_stack / BPF_REG_SIZE;              \
 163              iter++, reg = bpf_get_spilled_reg(iter, frame))
 164
 165 /* linked list of verifier states used to prune search */
 166 struct bpf_verifier_state_list {
 167         struct bpf_verifier_state state;
 168         struct bpf_verifier_state_list *next;
 169 };
 170
 171 /* Possible states for alu_state member. */
 172 #define BPF_ALU_SANITIZE_SRC            1U
 173 #define BPF_ALU_SANITIZE_DST            2U
 174 #define BPF_ALU_NEG_VALUE               (1U << 2)
 175 #define BPF_ALU_SANITIZE                (BPF_ALU_SANITIZE_SRC | \
 176                                          BPF_ALU_SANITIZE_DST)
 177
 178 struct bpf_insn_aux_data {
 179         union {
 180                 enum bpf_reg_type ptr_type;     /* pointer type for load/store insns */
 181                 unsigned long map_state;        /* pointer/poison value for maps */
 182                 s32 call_imm;                   /* saved imm field of call insn */
 183                 u32 alu_limit;                  /* limit for add/sub register with pointer */
 184         };
 185         int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
 186         int sanitize_stack_off; /* stack slot to be cleared */
 187         bool seen; /* this insn was processed by the verifier */
 188         u8 alu_state; /* used in combination with alu_limit */
 189 };
 190
 191 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
 192
 193 #define BPF_VERIFIER_TMP_LOG_SIZE       1024
 194
 195 struct bpf_verifier_log {
 196         u32 level;
 197         char kbuf[BPF_VERIFIER_TMP_LOG_SIZE];
 198         char __user *ubuf;
 199         u32 len_used;
 200         u32 len_total;
 201 };
 202
 203 static inline bool bpf_verifier_log_full(const struct bpf_verifier_log *log)
 204 {
 205         return log->len_used >= log->len_total - 1;
 206 }
 207
 208 static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
 209 {
 210         return log->level && log->ubuf && !bpf_verifier_log_full(log);
 211 }
 212
 213 #define BPF_MAX_SUBPROGS 256
 214
 215 struct bpf_subprog_info {
 216         u32 start; /* insn idx of function entry point */
 217         u32 linfo_idx; /* The idx to the main_prog->aux->linfo */
 218         u16 stack_depth; /* max. stack depth used by this function */
 219 };
 220
 221 /* single container for all structs
 222  * one verifier_env per bpf_check() call
 223  */
 224 struct bpf_verifier_env {
 225         u32 insn_idx;
 226         u32 prev_insn_idx;
 227         struct bpf_prog *prog;          /* eBPF program being verified */
 228         const struct bpf_verifier_ops *ops;
 229         struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
 230         int stack_size;                 /* number of states to be processed */
 231         bool strict_alignment;          /* perform strict pointer alignment checks */
 232         struct bpf_verifier_state *cur_state; /* current verifier state */
 233         struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
 234         struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
 235         u32 used_map_cnt;               /* number of used maps */
 236         u32 id_gen;                     /* used to generate unique reg IDs */
 237         bool allow_ptr_leaks;
 238         bool seen_direct_write;
 239         struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
 240         const struct bpf_line_info *prev_linfo;
 241         struct bpf_verifier_log log;
 242         struct bpf_subprog_info subprog_info[BPF_MAX_SUBPROGS + 1];
 243         u32 subprog_cnt;
 244 };
 245
 246 __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,
 247                                       const char *fmt, va_list args);
 248 __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
 249                                            const char *fmt, ...);
 250
 251 static inline struct bpf_func_state *cur_func(struct bpf_verifier_env *env)
 252 {
 253         struct bpf_verifier_state *cur = env->cur_state;
 254
 255         return cur->frame[cur->curframe];
 256 }
 257
 258 static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
 259 {
 260         return cur_func(env)->regs;
 261 }
 262
 263 int bpf_prog_offload_verifier_prep(struct bpf_prog *prog);
 264 int bpf_prog_offload_verify_insn(struct bpf_verifier_env *env,
 265                                  int insn_idx, int prev_insn_idx);
 266 int bpf_prog_offload_finalize(struct bpf_verifier_env *env);
 267
 268 #endif /* _LINUX_BPF_VERIFIER_H */