1 /* 2 * Seccomp BPF helper functions 3 * 4 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org> 5 * Author: Will Drewry <wad@chromium.org> 6 * 7 * The code may be used by anyone for any purpose, 8 * and can serve as a starting point for developing 9 * applications using prctl(PR_ATTACH_SECCOMP_FILTER). 10 */ 11 12 #include <stdio.h> 13 #include <string.h> 14 15 #include "bpf-helper.h" 16 17 int bpf_resolve_jumps(struct bpf_labels *labels, 18 struct sock_filter *filter, size_t count) 19 { 20 struct sock_filter *begin = filter; 21 __u8 insn = count - 1; 22 23 if (count < 1) 24 return -1; 25 /* 26 * Walk it once, backwards, to build the label table and do fixups. 27 * Since backward jumps are disallowed by BPF, this is easy. 28 */ 29 filter += insn; 30 for (; filter >= begin; --insn, --filter) { 31 if (filter->code != (BPF_JMP+BPF_JA)) 32 continue; 33 switch ((filter->jt<<8)|filter->jf) { 34 case (JUMP_JT<<8)|JUMP_JF: 35 if (labels->labels[filter->k].location == 0xffffffff) { 36 fprintf(stderr, "Unresolved label: '%s'\n", 37 labels->labels[filter->k].label); 38 return 1; 39 } 40 filter->k = labels->labels[filter->k].location - 41 (insn + 1); 42 filter->jt = 0; 43 filter->jf = 0; 44 continue; 45 case (LABEL_JT<<8)|LABEL_JF: 46 if (labels->labels[filter->k].location != 0xffffffff) { 47 fprintf(stderr, "Duplicate label use: '%s'\n", 48 labels->labels[filter->k].label); 49 return 1; 50 } 51 labels->labels[filter->k].location = insn; 52 filter->k = 0; /* fall through */ 53 filter->jt = 0; 54 filter->jf = 0; 55 continue; 56 } 57 } 58 return 0; 59 } 60 61 /* Simple lookup table for labels. */ 62 __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label) 63 { 64 struct __bpf_label *begin = labels->labels, *end; 65 int id; 66 if (labels->count == 0) { 67 begin->label = label; 68 begin->location = 0xffffffff; 69 labels->count++; 70 return 0; 71 } 72 end = begin + labels->count; 73 for (id = 0; begin < end; ++begin, ++id) { 74 if (!strcmp(label, begin->label)) 75 return id; 76 } 77 begin->label = label; 78 begin->location = 0xffffffff; 79 labels->count++; 80 return id; 81 } 82 83 void seccomp_bpf_print(struct sock_filter *filter, size_t count) 84 { 85 struct sock_filter *end = filter + count; 86 for ( ; filter < end; ++filter) 87 printf("{ code=%u,jt=%u,jf=%u,k=%u },\n", 88 filter->code, filter->jt, filter->jf, filter->k); 89 } 90