granicus.if.org Git - strace/blob - bpf_filter.c

   1 /*
   2  * Decoder of classic BPF programs.
   3  *
   4  * Copyright (c) 2015-2017 Dmitry V. Levin <ldv@altlinux.org>
   5  * Copyright (c) 2017-2018 The strace developers.
   6  * All rights reserved.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. The name of the author may not be used to endorse or promote products
  17  *    derived from this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  20  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  21  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  22  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  23  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  24  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  28  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  29  */
  30
  31 #include "defs.h"
  32
  33 #include "bpf_filter.h"
  34 #include "bpf_fprog.h"
  35
  36 #include <linux/filter.h>
  37
  38 #include "xlat/bpf_class.h"
  39 #include "xlat/bpf_miscop.h"
  40 #include "xlat/bpf_mode.h"
  41 #include "xlat/bpf_op_alu.h"
  42 #include "xlat/bpf_op_jmp.h"
  43 #include "xlat/bpf_rval.h"
  44 #include "xlat/bpf_size.h"
  45 #include "xlat/bpf_src.h"
  46
  47 #include "xlat/ebpf_class.h"
  48 #include "xlat/ebpf_mode.h"
  49 #include "xlat/ebpf_op_alu.h"
  50 #include "xlat/ebpf_op_jmp.h"
  51 #include "xlat/ebpf_size.h"
  52
  53 void
  54 print_bpf_filter_code(const uint16_t code, bool extended)
  55 {
  56         const struct xlat *mode = extended ? ebpf_mode : bpf_mode;
  57         uint16_t i = code & ~BPF_CLASS(code);
  58
  59         if (extended)
  60                 printxval_index(ebpf_class, BPF_CLASS(code), "BPF_???");
  61         else
  62                 printxval_index(bpf_class, BPF_CLASS(code), "BPF_???");
  63         switch (BPF_CLASS(code)) {
  64         case BPF_ST:
  65         case BPF_STX:
  66                 if (!extended) {
  67                         if (i) {
  68                                 tprintf("|%#x", i);
  69                                 tprints_comment("BPF_???");
  70                         }
  71                         break;
  72                 }
  73                 ATTRIBUTE_FALLTHROUGH; /* extended == true */
  74
  75         case BPF_LD:
  76         case BPF_LDX:
  77                 tprints("|");
  78                 printxvals(BPF_SIZE(code), "BPF_???",
  79                            bpf_size, extended ? ebpf_size : NULL, NULL);
  80                 tprints("|");
  81                 printxval(mode, BPF_MODE(code), "BPF_???");
  82                 break;
  83
  84         case BPF_MISC: /* BPF_ALU64 in eBPF */
  85                 if (!extended) {
  86                         tprints("|");
  87                         printxval(bpf_miscop, BPF_MISCOP(code), "BPF_???");
  88                         i &= ~BPF_MISCOP(code);
  89                         if (i) {
  90                                 tprintf("|%#x", i);
  91                                 tprints_comment("BPF_???");
  92                         }
  93                         break;
  94                 }
  95                 ATTRIBUTE_FALLTHROUGH; /* extended == true */
  96
  97         case BPF_ALU:
  98                 tprints("|");
  99                 printxval(bpf_src, BPF_SRC(code), "BPF_???");
 100                 tprints("|");
 101                 printxvals(BPF_OP(code), "BPF_???",
 102                            bpf_op_alu,
 103                            extended ? ebpf_op_alu : NULL, NULL);
 104                 break;
 105
 106         case BPF_JMP:
 107                 tprints("|");
 108                 printxval(bpf_src, BPF_SRC(code), "BPF_???");
 109                 tprints("|");
 110                 printxvals(BPF_OP(code), "BPF_???",
 111                            bpf_op_jmp, extended ? ebpf_op_jmp : NULL, NULL);
 112                 break;
 113
 114         case BPF_RET: /* Reserved in eBPF */
 115                 if (!extended) {
 116                         tprints("|");
 117                         printxval(bpf_rval, BPF_RVAL(code), "BPF_???");
 118                         i &= ~BPF_RVAL(code);
 119                 }
 120
 121                 if (i) {
 122                         tprintf("|%#x", i);
 123                         tprints_comment("BPF_???");
 124                 }
 125
 126                 break;
 127         }
 128 }
 129
 130 static void
 131 print_bpf_filter_stmt(const struct bpf_filter_block *const filter,
 132                       const print_bpf_filter_fn print_k)
 133 {
 134         tprints("BPF_STMT(");
 135         print_bpf_filter_code(filter->code, false);
 136         tprints(", ");
 137         if (!print_k || !print_k(filter))
 138                 tprintf("%#x", filter->k);
 139         tprints(")");
 140 }
 141
 142 static void
 143 print_bpf_filter_jump(const struct bpf_filter_block *const filter)
 144 {
 145         tprints("BPF_JUMP(");
 146         print_bpf_filter_code(filter->code, false);
 147         tprintf(", %#x, %#x, %#x)", filter->k, filter->jt, filter->jf);
 148 }
 149
 150 struct bpf_filter_block_data {
 151         const print_bpf_filter_fn fn;
 152         unsigned int count;
 153 };
 154
 155 static bool
 156 print_bpf_filter_block(struct tcb *const tcp, void *const elem_buf,
 157                        const size_t elem_size, void *const data)
 158 {
 159         const struct bpf_filter_block *const filter = elem_buf;
 160         struct bpf_filter_block_data *const fbd = data;
 161
 162         if (fbd->count++ >= BPF_MAXINSNS) {
 163                 tprints("...");
 164                 return false;
 165         }
 166
 167         if (filter->jt || filter->jf)
 168                 print_bpf_filter_jump(filter);
 169         else
 170                 print_bpf_filter_stmt(filter, fbd->fn);
 171
 172         return true;
 173 }
 174
 175 void
 176 print_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
 177                 const unsigned short len, const print_bpf_filter_fn print_k)
 178 {
 179         if (abbrev(tcp)) {
 180                 printaddr(addr);
 181         } else {
 182                 struct bpf_filter_block_data fbd = { .fn = print_k };
 183                 struct bpf_filter_block filter;
 184
 185                 print_array(tcp, addr, len, &filter, sizeof(filter),
 186                             tfetch_mem, print_bpf_filter_block, &fbd);
 187         }
 188 }
 189
 190 void
 191 decode_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
 192                  const print_bpf_filter_fn print_k)
 193 {
 194         struct bpf_fprog fprog;
 195
 196         if (fetch_bpf_fprog(tcp, addr, &fprog)) {
 197                 tprintf("{len=%hu, filter=", fprog.len);
 198                 print_bpf_fprog(tcp, fprog.filter, fprog.len, print_k);
 199                 tprints("}");
 200         }
 201 }