include/linux/bpf_verifier.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
   3  */
   4 #ifndef _LINUX_BPF_VERIFIER_H
   5 #define _LINUX_BPF_VERIFIER_H 1
   6
   7 #include <linux/bpf.h> /* for enum bpf_reg_type */
   8 #include <linux/filter.h> /* for MAX_BPF_STACK */
   9 #include <linux/tnum.h>
  10
  11 /* Maximum variable offset umax_value permitted when resolving memory accesses.
  12  * In practice this is far bigger than any realistic pointer offset; this limit
  13  * ensures that umax_value + (int)off + (int)size cannot overflow a u64.
  14  */
  15 #define BPF_MAX_VAR_OFF (1 << 29)
  16 /* Maximum variable size permitted for ARG_CONST_SIZE[_OR_ZERO].  This ensures
  17  * that converting umax_value to int cannot overflow.
  18  */
  19 #define BPF_MAX_VAR_SIZ (1 << 29)
  20
  21 /* Liveness marks, used for registers and spilled-regs (in stack slots).
  22  * Read marks propagate upwards until they find a write mark; they record that
  23  * "one of this state's descendants read this reg" (and therefore the reg is
  24  * relevant for states_equal() checks).
  25  * Write marks collect downwards and do not propagate; they record that "the
  26  * straight-line code that reached this state (from its parent) wrote this reg"
  27  * (and therefore that reads propagated from this state or its descendants
  28  * should not propagate to its parent).
  29  * A state with a write mark can receive read marks; it just won't propagate
  30  * them to its parent, since the write mark is a property, not of the state,
  31  * but of the link between it and its parent.  See mark_reg_read() and
  32  * mark_stack_slot_read() in kernel/bpf/verifier.c.
  33  */
  34 enum bpf_reg_liveness {
  35         REG_LIVE_NONE = 0, /* reg hasn't been read or written this branch */
  36         REG_LIVE_READ, /* reg was read, so we're sensitive to initial value */
  37         REG_LIVE_WRITTEN, /* reg was written first, screening off later reads */
  38         REG_LIVE_DONE = 4, /* liveness won't be updating this register anymore */
  39 };
  40
  41 struct bpf_reg_state {
  42         /* Ordering of fields matters.  See states_equal() */
  43         enum bpf_reg_type type;
  44         union {
  45                 /* valid when type == PTR_TO_PACKET */
  46                 u16 range;
  47
  48                 /* valid when type == CONST_PTR_TO_MAP | PTR_TO_MAP_VALUE |
  49                  *   PTR_TO_MAP_VALUE_OR_NULL
  50                  */
  51                 struct bpf_map *map_ptr;
  52
  53                 /* Max size from any of the above. */
  54                 unsigned long raw;
  55         };
  56         /* Fixed part of pointer offset, pointer types only */
  57         s32 off;
  58         /* For PTR_TO_PACKET, used to find other pointers with the same variable
  59          * offset, so they can share range knowledge.
  60          * For PTR_TO_MAP_VALUE_OR_NULL this is used to share which map value we
  61          * came from, when one is tested for != NULL.
  62          * For PTR_TO_SOCKET this is used to share which pointers retain the
  63          * same reference to the socket, to determine proper reference freeing.
  64          */
  65         u32 id;
  66         /* PTR_TO_SOCKET and PTR_TO_TCP_SOCK could be a ptr returned
  67          * from a pointer-cast helper, bpf_sk_fullsock() and
  68          * bpf_tcp_sock().
  69          *
  70          * Consider the following where "sk" is a reference counted
  71          * pointer returned from "sk = bpf_sk_lookup_tcp();":
  72          *
  73          * 1: sk = bpf_sk_lookup_tcp();
  74          * 2: if (!sk) { return 0; }
  75          * 3: fullsock = bpf_sk_fullsock(sk);
  76          * 4: if (!fullsock) { bpf_sk_release(sk); return 0; }
  77          * 5: tp = bpf_tcp_sock(fullsock);
  78          * 6: if (!tp) { bpf_sk_release(sk); return 0; }
  79          * 7: bpf_sk_release(sk);
  80          * 8: snd_cwnd = tp->snd_cwnd;  // verifier will complain
  81          *
  82          * After bpf_sk_release(sk) at line 7, both "fullsock" ptr and
  83          * "tp" ptr should be invalidated also.  In order to do that,
  84          * the reg holding "fullsock" and "sk" need to remember
  85          * the original refcounted ptr id (i.e. sk_reg->id) in ref_obj_id
  86          * such that the verifier can reset all regs which have
  87          * ref_obj_id matching the sk_reg->id.
  88          *
  89          * sk_reg->ref_obj_id is set to sk_reg->id at line 1.
  90          * sk_reg->id will stay as NULL-marking purpose only.
  91          * After NULL-marking is done, sk_reg->id can be reset to 0.
  92          *
  93          * After "fullsock = bpf_sk_fullsock(sk);" at line 3,
  94          * fullsock_reg->ref_obj_id is set to sk_reg->ref_obj_id.
  95          *
  96          * After "tp = bpf_tcp_sock(fullsock);" at line 5,
  97          * tp_reg->ref_obj_id is set to fullsock_reg->ref_obj_id
  98          * which is the same as sk_reg->ref_obj_id.
  99          *
 100          * From the verifier perspective, if sk, fullsock and tp
 101          * are not NULL, they are the same ptr with different
 102          * reg->type.  In particular, bpf_sk_release(tp) is also
 103          * allowed and has the same effect as bpf_sk_release(sk).
 104          */
 105         u32 ref_obj_id;
 106         /* For scalar types (SCALAR_VALUE), this represents our knowledge of
 107          * the actual value.
 108          * For pointer types, this represents the variable part of the offset
 109          * from the pointed-to object, and is shared with all bpf_reg_states
 110          * with the same id as us.
 111          */
 112         struct tnum var_off;
 113         /* Used to determine if any memory access using this register will
 114          * result in a bad access.
 115          * These refer to the same value as var_off, not necessarily the actual
 116          * contents of the register.
 117          */
 118         s64 smin_value; /* minimum possible (s64)value */
 119         s64 smax_value; /* maximum possible (s64)value */
 120         u64 umin_value; /* minimum possible (u64)value */
 121         u64 umax_value; /* maximum possible (u64)value */
 122         /* parentage chain for liveness checking */
 123         struct bpf_reg_state *parent;
 124         /* Inside the callee two registers can be both PTR_TO_STACK like
 125          * R1=fp-8 and R2=fp-8, but one of them points to this function stack
 126          * while another to the caller's stack. To differentiate them 'frameno'
 127          * is used which is an index in bpf_verifier_state->frame[] array
 128          * pointing to bpf_func_state.
 129          */
 130         u32 frameno;
 131         enum bpf_reg_liveness live;
 132 };
 133
 134 enum bpf_stack_slot_type {
 135         STACK_INVALID,    /* nothing was stored in this stack slot */
 136         STACK_SPILL,      /* register spilled into stack */
 137         STACK_MISC,       /* BPF program wrote some data into this slot */
 138         STACK_ZERO,       /* BPF program wrote constant zero */
 139 };
 140
 141 #define BPF_REG_SIZE 8  /* size of eBPF register in bytes */
 142
 143 struct bpf_stack_state {
 144         struct bpf_reg_state spilled_ptr;
 145         u8 slot_type[BPF_REG_SIZE];
 146 };
 147
 148 struct bpf_reference_state {
 149         /* Track each reference created with a unique id, even if the same
 150          * instruction creates the reference multiple times (eg, via CALL).
 151          */
 152         int id;
 153         /* Instruction where the allocation of this reference occurred. This
 154          * is used purely to inform the user of a reference leak.
 155          */
 156         int insn_idx;
 157 };
 158
 159 /* state of the program:
 160  * type of all registers and stack info
 161  */
 162 struct bpf_func_state {
 163         struct bpf_reg_state regs[MAX_BPF_REG];
 164         /* index of call instruction that called into this func */
 165         int callsite;
 166         /* stack frame number of this function state from pov of
 167          * enclosing bpf_verifier_state.
 168          * 0 = main function, 1 = first callee.
 169          */
 170         u32 frameno;
 171         /* subprog number == index within subprog_stack_depth
 172          * zero == main subprog
 173          */
 174         u32 subprogno;
 175
 176         /* The following fields should be last. See copy_func_state() */
 177         int acquired_refs;
 178         struct bpf_reference_state *refs;
 179         int allocated_stack;
 180         struct bpf_stack_state *stack;
 181 };
 182
 183 #define MAX_CALL_FRAMES 8
 184 struct bpf_verifier_state {
 185         /* call stack tracking */
 186         struct bpf_func_state *frame[MAX_CALL_FRAMES];
 187         u32 curframe;
 188         u32 active_spin_lock;
 189         bool speculative;
 190 };
 191
 192 #define bpf_get_spilled_reg(slot, frame)                                \
 193         (((slot < frame->allocated_stack / BPF_REG_SIZE) &&             \
 194           (frame->stack[slot].slot_type[0] == STACK_SPILL))             \
 195          ? &frame->stack[slot].spilled_ptr : NULL)
 196
 197 /* Iterate over 'frame', setting 'reg' to either NULL or a spilled register. */
 198 #define bpf_for_each_spilled_reg(iter, frame, reg)                      \
 199         for (iter = 0, reg = bpf_get_spilled_reg(iter, frame);          \
 200              iter < frame->allocated_stack / BPF_REG_SIZE;              \
 201              iter++, reg = bpf_get_spilled_reg(iter, frame))
 202
 203 /* linked list of verifier states used to prune search */
 204 struct bpf_verifier_state_list {
 205         struct bpf_verifier_state state;
 206         struct bpf_verifier_state_list *next;
 207         int miss_cnt, hit_cnt;
 208 };
 209
 210 /* Possible states for alu_state member. */
 211 #define BPF_ALU_SANITIZE_SRC            1U
 212 #define BPF_ALU_SANITIZE_DST            2U
 213 #define BPF_ALU_NEG_VALUE               (1U << 2)
 214 #define BPF_ALU_NON_POINTER             (1U << 3)
 215 #define BPF_ALU_SANITIZE                (BPF_ALU_SANITIZE_SRC | \
 216                                          BPF_ALU_SANITIZE_DST)
 217
 218 struct bpf_insn_aux_data {
 219         union {
 220                 enum bpf_reg_type ptr_type;     /* pointer type for load/store insns */
 221                 unsigned long map_state;        /* pointer/poison value for maps */
 222                 s32 call_imm;                   /* saved imm field of call insn */
 223                 u32 alu_limit;                  /* limit for add/sub register with pointer */
 224                 struct {
 225                         u32 map_index;          /* index into used_maps[] */
 226                         u32 map_off;            /* offset from value base address */
 227                 };
 228         };
 229         int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
 230         int sanitize_stack_off; /* stack slot to be cleared */
 231         bool seen; /* this insn was processed by the verifier */
 232         u8 alu_state; /* used in combination with alu_limit */
 233         unsigned int orig_idx; /* original instruction index */
 234 };
 235
 236 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
 237
 238 #define BPF_VERIFIER_TMP_LOG_SIZE       1024
 239
 240 struct bpf_verifier_log {
 241         u32 level;
 242         char kbuf[BPF_VERIFIER_TMP_LOG_SIZE];
 243         char __user *ubuf;
 244         u32 len_used;
 245         u32 len_total;
 246 };
 247
 248 static inline bool bpf_verifier_log_full(const struct bpf_verifier_log *log)
 249 {
 250         return log->len_used >= log->len_total - 1;
 251 }
 252
 253 #define BPF_LOG_LEVEL1  1
 254 #define BPF_LOG_LEVEL2  2
 255 #define BPF_LOG_STATS   4
 256 #define BPF_LOG_LEVEL   (BPF_LOG_LEVEL1 | BPF_LOG_LEVEL2)
 257 #define BPF_LOG_MASK    (BPF_LOG_LEVEL | BPF_LOG_STATS)
 258
 259 static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
 260 {
 261         return log->level && log->ubuf && !bpf_verifier_log_full(log);
 262 }
 263
 264 #define BPF_MAX_SUBPROGS 256
 265
 266 struct bpf_subprog_info {
 267         u32 start; /* insn idx of function entry point */
 268         u32 linfo_idx; /* The idx to the main_prog->aux->linfo */
 269         u16 stack_depth; /* max. stack depth used by this function */
 270 };
 271
 272 /* single container for all structs
 273  * one verifier_env per bpf_check() call
 274  */
 275 struct bpf_verifier_env {
 276         u32 insn_idx;
 277         u32 prev_insn_idx;
 278         struct bpf_prog *prog;          /* eBPF program being verified */
 279         const struct bpf_verifier_ops *ops;
 280         struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
 281         int stack_size;                 /* number of states to be processed */
 282         bool strict_alignment;          /* perform strict pointer alignment checks */
 283         struct bpf_verifier_state *cur_state; /* current verifier state */
 284         struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
 285         struct bpf_verifier_state_list *free_list;
 286         struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
 287         u32 used_map_cnt;               /* number of used maps */
 288         u32 id_gen;                     /* used to generate unique reg IDs */
 289         bool allow_ptr_leaks;
 290         bool seen_direct_write;
 291         struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
 292         const struct bpf_line_info *prev_linfo;
 293         struct bpf_verifier_log log;
 294         struct bpf_subprog_info subprog_info[BPF_MAX_SUBPROGS + 1];
 295         struct {
 296                 int *insn_state;
 297                 int *insn_stack;
 298                 int cur_stack;
 299         } cfg;
 300         u32 subprog_cnt;
 301         /* number of instructions analyzed by the verifier */
 302         u32 insn_processed;
 303         /* total verification time */
 304         u64 verification_time;
 305         /* maximum number of verifier states kept in 'branching' instructions */
 306         u32 max_states_per_insn;
 307         /* total number of allocated verifier states */
 308         u32 total_states;
 309         /* some states are freed during program analysis.
 310          * this is peak number of states. this number dominates kernel
 311          * memory consumption during verification
 312          */
 313         u32 peak_states;
 314         /* longest register parentage chain walked for liveness marking */
 315         u32 longest_mark_read_walk;
 316 };
 317
 318 __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,
 319                                       const char *fmt, va_list args);
 320 __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
 321                                            const char *fmt, ...);
 322
 323 static inline struct bpf_func_state *cur_func(struct bpf_verifier_env *env)
 324 {
 325         struct bpf_verifier_state *cur = env->cur_state;
 326
 327         return cur->frame[cur->curframe];
 328 }
 329
 330 static inline struct bpf_reg_state *cur_regs(struct bpf_verifier_env *env)
 331 {
 332         return cur_func(env)->regs;
 333 }
 334
 335 int bpf_prog_offload_verifier_prep(struct bpf_prog *prog);
 336 int bpf_prog_offload_verify_insn(struct bpf_verifier_env *env,
 337                                  int insn_idx, int prev_insn_idx);
 338 int bpf_prog_offload_finalize(struct bpf_verifier_env *env);
 339 void
 340 bpf_prog_offload_replace_insn(struct bpf_verifier_env *env, u32 off,
 341                               struct bpf_insn *insn);
 342 void
 343 bpf_prog_offload_remove_insns(struct bpf_verifier_env *env, u32 off, u32 cnt);
 344
 345 #endif /* _LINUX_BPF_VERIFIER_H */