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 #include "xlat/bpf_class.h"
  38 #include "xlat/bpf_miscop.h"
  39 #include "xlat/bpf_mode.h"
  40 #include "xlat/bpf_op_alu.h"
  41 #include "xlat/bpf_op_jmp.h"
  42 #include "xlat/bpf_rval.h"
  43 #include "xlat/bpf_size.h"
  44 #include "xlat/bpf_src.h"
  45
  46 static void
  47 print_bpf_filter_code(const uint16_t code)
  48 {
  49         uint16_t i = code & ~BPF_CLASS(code);
  50
  51         printxval(bpf_class, BPF_CLASS(code), "BPF_???");
  52         switch (BPF_CLASS(code)) {
  53         case BPF_LD:
  54         case BPF_LDX:
  55                 tprints("|");
  56                 printxval(bpf_size, BPF_SIZE(code), "BPF_???");
  57                 tprints("|");
  58                 printxval(bpf_mode, BPF_MODE(code), "BPF_???");
  59                 break;
  60         case BPF_ST:
  61         case BPF_STX:
  62                 if (i) {
  63                         tprintf("|%#x", i);
  64                         tprints_comment("BPF_???");
  65                 }
  66                 break;
  67         case BPF_ALU:
  68                 tprints("|");
  69                 printxval(bpf_src, BPF_SRC(code), "BPF_???");
  70                 tprints("|");
  71                 printxval(bpf_op_alu, BPF_OP(code), "BPF_???");
  72                 break;
  73         case BPF_JMP:
  74                 tprints("|");
  75                 printxval(bpf_src, BPF_SRC(code), "BPF_???");
  76                 tprints("|");
  77                 printxval(bpf_op_jmp, BPF_OP(code), "BPF_???");
  78                 break;
  79         case BPF_RET:
  80                 tprints("|");
  81                 printxval(bpf_rval, BPF_RVAL(code), "BPF_???");
  82                 i &= ~BPF_RVAL(code);
  83                 if (i) {
  84                         tprintf("|%#x", i);
  85                         tprints_comment("BPF_???");
  86                 }
  87                 break;
  88         case BPF_MISC:
  89                 tprints("|");
  90                 printxval(bpf_miscop, BPF_MISCOP(code), "BPF_???");
  91                 i &= ~BPF_MISCOP(code);
  92                 if (i) {
  93                         tprintf("|%#x", i);
  94                         tprints_comment("BPF_???");
  95                 }
  96                 break;
  97         }
  98 }
  99
 100 static void
 101 print_bpf_filter_stmt(const struct bpf_filter_block *const filter,
 102                       const print_bpf_filter_fn print_k)
 103 {
 104         tprints("BPF_STMT(");
 105         print_bpf_filter_code(filter->code);
 106         tprints(", ");
 107         if (!print_k || !print_k(filter))
 108                 tprintf("%#x", filter->k);
 109         tprints(")");
 110 }
 111
 112 static void
 113 print_bpf_filter_jump(const struct bpf_filter_block *const filter)
 114 {
 115         tprints("BPF_JUMP(");
 116         print_bpf_filter_code(filter->code);
 117         tprintf(", %#x, %#x, %#x)", filter->k, filter->jt, filter->jf);
 118 }
 119
 120 struct bpf_filter_block_data {
 121         const print_bpf_filter_fn fn;
 122         unsigned int count;
 123 };
 124
 125 static bool
 126 print_bpf_filter_block(struct tcb *const tcp, void *const elem_buf,
 127                        const size_t elem_size, void *const data)
 128 {
 129         const struct bpf_filter_block *const filter = elem_buf;
 130         struct bpf_filter_block_data *const fbd = data;
 131
 132         if (fbd->count++ >= BPF_MAXINSNS) {
 133                 tprints("...");
 134                 return false;
 135         }
 136
 137         if (filter->jt || filter->jf)
 138                 print_bpf_filter_jump(filter);
 139         else
 140                 print_bpf_filter_stmt(filter, fbd->fn);
 141
 142         return true;
 143 }
 144
 145 void
 146 print_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
 147                 const unsigned short len, const print_bpf_filter_fn print_k)
 148 {
 149         if (abbrev(tcp)) {
 150                 printaddr(addr);
 151         } else {
 152                 struct bpf_filter_block_data fbd = { .fn = print_k };
 153                 struct bpf_filter_block filter;
 154
 155                 print_array(tcp, addr, len, &filter, sizeof(filter),
 156                             umoven_or_printaddr, print_bpf_filter_block, &fbd);
 157         }
 158 }
 159
 160 void
 161 decode_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
 162                  const print_bpf_filter_fn print_k)
 163 {
 164         struct bpf_fprog fprog;
 165
 166         if (fetch_bpf_fprog(tcp, addr, &fprog)) {
 167                 tprintf("{len=%hu, filter=", fprog.len);
 168                 print_bpf_fprog(tcp, fprog.filter, fprog.len, print_k);
 169                 tprints("}");
 170         }
 171 }