Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 1 | /* Copyright (c) 2012 The Chromium OS Authors. All rights reserved. |
| 2 | * Use of this source code is governed by a BSD-style license that can be |
| 3 | * found in the LICENSE file. |
| 4 | */ |
| 5 | |
| 6 | #include <stdint.h> |
| 7 | #include <stdio.h> |
| 8 | #include <stdlib.h> |
| 9 | #include <string.h> |
| 10 | |
| 11 | #include "bpf.h" |
| 12 | |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 13 | /* Basic BPF instruction setter. */ |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 14 | inline size_t set_bpf_instr(struct sock_filter *instr, |
| 15 | unsigned short code, unsigned int k, |
| 16 | unsigned char jt, unsigned char jf) |
| 17 | { |
| 18 | instr->code = code; |
| 19 | instr->k = k; |
| 20 | instr->jt = jt; |
| 21 | instr->jf = jf; |
| 22 | return 1U; |
| 23 | } |
| 24 | |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 25 | /* Architecture validation. */ |
| 26 | size_t bpf_validate_arch(struct sock_filter *filter) |
| 27 | { |
| 28 | struct sock_filter *curr_block = filter; |
| 29 | set_bpf_stmt(curr_block++, BPF_LD+BPF_W+BPF_ABS, arch_nr); |
| 30 | set_bpf_jump(curr_block++, |
| 31 | BPF_JMP+BPF_JEQ+BPF_K, ARCH_NR, SKIP, NEXT); |
| 32 | set_bpf_ret_kill(curr_block++); |
| 33 | return curr_block - filter; |
| 34 | } |
| 35 | |
| 36 | /* Syscall number eval functions. */ |
| 37 | size_t bpf_allow_syscall(struct sock_filter *filter, int nr) |
| 38 | { |
| 39 | struct sock_filter *curr_block = filter; |
| 40 | set_bpf_jump(curr_block++, BPF_JMP+BPF_JEQ+BPF_K, nr, NEXT, SKIP); |
| 41 | set_bpf_stmt(curr_block++, BPF_RET+BPF_K, SECCOMP_RET_ALLOW); |
| 42 | return curr_block - filter; |
| 43 | } |
| 44 | |
| 45 | size_t bpf_allow_syscall_args(struct sock_filter *filter, |
| 46 | int nr, unsigned int id) |
| 47 | { |
| 48 | struct sock_filter *curr_block = filter; |
| 49 | set_bpf_jump(curr_block++, BPF_JMP+BPF_JEQ+BPF_K, nr, NEXT, SKIP); |
| 50 | set_bpf_jump_lbl(curr_block++, id); |
| 51 | return curr_block - filter; |
| 52 | } |
| 53 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 54 | /* Size-aware arg loaders. */ |
| 55 | #if defined(BITS32) |
| 56 | size_t bpf_load_arg(struct sock_filter *filter, int argidx) |
| 57 | { |
| 58 | set_bpf_stmt(filter, BPF_LD+BPF_W+BPF_ABS, LO_ARG(argidx)); |
| 59 | return 1U; |
| 60 | } |
| 61 | #elif defined(BITS64) |
| 62 | size_t bpf_load_arg(struct sock_filter *filter, int argidx) |
| 63 | { |
| 64 | struct sock_filter *curr_block = filter; |
| 65 | set_bpf_stmt(curr_block++, BPF_LD+BPF_W+BPF_ABS, LO_ARG(argidx)); |
| 66 | set_bpf_stmt(curr_block++, BPF_ST, 0); /* lo -> M[0] */ |
| 67 | set_bpf_stmt(curr_block++, BPF_LD+BPF_W+BPF_ABS, HI_ARG(argidx)); |
| 68 | set_bpf_stmt(curr_block++, BPF_ST, 1); /* hi -> M[1] */ |
| 69 | return curr_block - filter; |
| 70 | } |
| 71 | #endif |
| 72 | |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 73 | /* Size-aware equality comparison. */ |
Jorge Lucangeli Obes | edb1d8e | 2012-04-26 10:05:09 -0700 | [diff] [blame] | 74 | size_t bpf_comp_jeq32(struct sock_filter *filter, unsigned long c, |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 75 | unsigned char jt, unsigned char jf) |
| 76 | { |
Jorge Lucangeli Obes | edb1d8e | 2012-04-26 10:05:09 -0700 | [diff] [blame] | 77 | unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); |
| 78 | set_bpf_jump(filter, BPF_JMP+BPF_JEQ+BPF_K, lo, jt, jf); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 79 | return 1U; |
| 80 | } |
| 81 | |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 82 | /* |
| 83 | * On 64 bits, we have to do two 32-bit comparisons. |
| 84 | * We jump true when *both* comparisons are true. |
| 85 | */ |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 86 | size_t bpf_comp_jeq64(struct sock_filter *filter, uint64_t c, |
| 87 | unsigned char jt, unsigned char jf) |
| 88 | { |
| 89 | unsigned int lo = (unsigned int)(c & 0xFFFFFFFF); |
| 90 | unsigned int hi = (unsigned int)(c >> 32); |
| 91 | |
| 92 | struct sock_filter *curr_block = filter; |
| 93 | |
| 94 | /* bpf_load_arg leaves |hi| in A */ |
| 95 | curr_block += bpf_comp_jeq32(curr_block, hi, NEXT, SKIPN(2) + jf); |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 96 | set_bpf_stmt(curr_block++, BPF_LD+BPF_MEM, 0); /* swap in |lo| */ |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 97 | curr_block += bpf_comp_jeq32(curr_block, lo, jt, jf); |
| 98 | |
| 99 | return curr_block - filter; |
| 100 | } |
| 101 | |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 102 | /* Size-aware bitwise AND. */ |
| 103 | size_t bpf_comp_jset32(struct sock_filter *filter, unsigned long mask, |
| 104 | unsigned char jt, unsigned char jf) |
| 105 | { |
| 106 | unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF); |
| 107 | set_bpf_jump(filter, BPF_JMP+BPF_JSET+BPF_K, mask_lo, jt, jf); |
| 108 | return 1U; |
| 109 | } |
| 110 | |
| 111 | /* |
| 112 | * On 64 bits, we have to do two 32-bit bitwise ANDs. |
| 113 | * We jump true when *either* bitwise AND is true (non-zero). |
| 114 | */ |
| 115 | size_t bpf_comp_jset64(struct sock_filter *filter, uint64_t mask, |
| 116 | unsigned char jt, unsigned char jf) |
| 117 | { |
| 118 | unsigned int mask_lo = (unsigned int)(mask & 0xFFFFFFFF); |
| 119 | unsigned int mask_hi = (unsigned int)(mask >> 32); |
| 120 | |
| 121 | struct sock_filter *curr_block = filter; |
| 122 | |
| 123 | /* bpf_load_arg leaves |hi| in A */ |
| 124 | curr_block += bpf_comp_jset32(curr_block, mask_hi, SKIPN(2) + jt, NEXT); |
| 125 | set_bpf_stmt(curr_block++, BPF_LD+BPF_MEM, 0); /* swap in |lo| */ |
| 126 | curr_block += bpf_comp_jset32(curr_block, mask_lo, jt, jf); |
| 127 | |
| 128 | return curr_block - filter; |
| 129 | } |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 130 | |
| 131 | size_t bpf_arg_comp(struct sock_filter **pfilter, |
| 132 | int op, int argidx, unsigned long c, unsigned int label_id) |
| 133 | { |
| 134 | struct sock_filter *filter = calloc(BPF_ARG_COMP_LEN + 1, |
| 135 | sizeof(struct sock_filter)); |
| 136 | struct sock_filter *curr_block = filter; |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 137 | size_t (*comp_function)(struct sock_filter *filter, unsigned long k, |
| 138 | unsigned char jt, unsigned char jf); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 139 | int flip = 0; |
| 140 | |
| 141 | /* Load arg */ |
| 142 | curr_block += bpf_load_arg(curr_block, argidx); |
| 143 | |
| 144 | /* Jump type */ |
| 145 | switch (op) { |
| 146 | case EQ: |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 147 | comp_function = bpf_comp_jeq; |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 148 | flip = 0; |
| 149 | break; |
| 150 | case NE: |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 151 | comp_function = bpf_comp_jeq; |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 152 | flip = 1; |
| 153 | break; |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 154 | case SET: |
| 155 | comp_function = bpf_comp_jset; |
| 156 | flip = 0; |
| 157 | break; |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 158 | default: |
| 159 | *pfilter = NULL; |
| 160 | return 0; |
| 161 | } |
| 162 | |
| 163 | /* |
| 164 | * It's easier for the rest of the code to have the true branch |
| 165 | * skip and the false branch fall through. |
| 166 | */ |
| 167 | unsigned char jt = flip ? NEXT : SKIP; |
| 168 | unsigned char jf = flip ? SKIP : NEXT; |
Jorge Lucangeli Obes | ffec891 | 2012-11-30 14:46:23 -0800 | [diff] [blame^] | 169 | curr_block += comp_function(curr_block, c, jt, jf); |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 170 | curr_block += set_bpf_jump_lbl(curr_block, label_id); |
| 171 | |
| 172 | *pfilter = filter; |
| 173 | return curr_block - filter; |
| 174 | } |
| 175 | |
| 176 | void dump_bpf_filter(struct sock_filter *filter, unsigned short len) |
| 177 | { |
| 178 | int i = 0; |
| 179 | |
| 180 | printf("len == %d\n", len); |
| 181 | printf("filter:\n"); |
| 182 | for (i = 0; i < len; i++) { |
| 183 | printf("%d: \t{ code=%#x, jt=%u, jf=%u, k=%#x \t}\n", |
| 184 | i, filter[i].code, filter[i].jt, filter[i].jf, filter[i].k); |
| 185 | } |
| 186 | } |
| 187 | |
| 188 | void dump_bpf_prog(struct sock_fprog *fprog) |
| 189 | { |
| 190 | struct sock_filter *filter = fprog->filter; |
| 191 | unsigned short len = fprog->len; |
| 192 | dump_bpf_filter(filter, len); |
| 193 | } |
| 194 | |
| 195 | int bpf_resolve_jumps(struct bpf_labels *labels, |
| 196 | struct sock_filter *filter, size_t count) |
| 197 | { |
| 198 | struct sock_filter *begin = filter; |
| 199 | __u8 insn = count - 1; |
| 200 | |
| 201 | if (count < 1) |
| 202 | return -1; |
| 203 | /* |
| 204 | * Walk it once, backwards, to build the label table and do fixups. |
| 205 | * Since backward jumps are disallowed by BPF, this is easy. |
| 206 | */ |
| 207 | for (filter += insn; filter >= begin; --insn, --filter) { |
| 208 | if (filter->code != (BPF_JMP+BPF_JA)) |
| 209 | continue; |
| 210 | switch ((filter->jt<<8)|filter->jf) { |
| 211 | case (JUMP_JT<<8)|JUMP_JF: |
| 212 | if (labels->labels[filter->k].location == 0xffffffff) { |
| 213 | fprintf(stderr, "Unresolved label: '%s'\n", |
| 214 | labels->labels[filter->k].label); |
| 215 | return 1; |
| 216 | } |
| 217 | filter->k = labels->labels[filter->k].location - |
| 218 | (insn + 1); |
| 219 | filter->jt = 0; |
| 220 | filter->jf = 0; |
| 221 | continue; |
| 222 | case (LABEL_JT<<8)|LABEL_JF: |
| 223 | if (labels->labels[filter->k].location != 0xffffffff) { |
| 224 | fprintf(stderr, "Duplicate label use: '%s'\n", |
| 225 | labels->labels[filter->k].label); |
| 226 | return 1; |
| 227 | } |
| 228 | labels->labels[filter->k].location = insn; |
| 229 | filter->k = 0; /* fall through */ |
| 230 | filter->jt = 0; |
| 231 | filter->jf = 0; |
| 232 | continue; |
| 233 | } |
| 234 | } |
| 235 | return 0; |
| 236 | } |
| 237 | |
| 238 | /* Simple lookup table for labels. */ |
| 239 | int bpf_label_id(struct bpf_labels *labels, const char *label) |
| 240 | { |
| 241 | struct __bpf_label *begin = labels->labels, *end; |
| 242 | int id; |
| 243 | if (labels->count == 0) { |
| 244 | begin->label = strndup(label, MAX_BPF_LABEL_LEN); |
| 245 | if (!begin->label) { |
| 246 | return -1; |
| 247 | } |
| 248 | begin->location = 0xffffffff; |
| 249 | labels->count++; |
| 250 | return 0; |
| 251 | } |
| 252 | end = begin + labels->count; |
| 253 | for (id = 0; begin < end; ++begin, ++id) { |
| 254 | if (!strcmp(label, begin->label)) |
| 255 | return id; |
| 256 | } |
| 257 | begin->label = strndup(label, MAX_BPF_LABEL_LEN); |
| 258 | if (!begin->label) { |
| 259 | return -1; |
| 260 | } |
| 261 | begin->location = 0xffffffff; |
| 262 | labels->count++; |
| 263 | return id; |
| 264 | } |
| 265 | |
| 266 | /* Free label strings. */ |
| 267 | void free_label_strings(struct bpf_labels *labels) |
| 268 | { |
Jorge Lucangeli Obes | d446726 | 2012-03-23 16:19:59 -0700 | [diff] [blame] | 269 | if (labels->count == 0) |
| 270 | return; |
| 271 | |
Jorge Lucangeli Obes | fc8ab53 | 2012-03-20 10:14:31 -0700 | [diff] [blame] | 272 | struct __bpf_label *begin = labels->labels, *end; |
| 273 | |
| 274 | end = begin + labels->count; |
| 275 | for (; begin < end; ++begin) { |
| 276 | if (begin->label) |
| 277 | free((void*)(begin->label)); |
| 278 | } |
| 279 | } |