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 <stdlib.h> 14 #include <string.h> 15 16 #include "bpf-helper.h" 17 18 int bpf_resolve_jumps(struct bpf_labels *labels, 19 struct sock_filter *filter, size_t count) 20 { 21 size_t i; 22 23 if (count < 1 || count > BPF_MAXINSNS) 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 for (i = 0; i < count; ++i) { 30 size_t offset = count - i - 1; 31 struct sock_filter *instr = &filter[offset]; 32 if (instr->code != (BPF_JMP+BPF_JA)) 33 continue; 34 switch ((instr->jt<<8)|instr->jf) { 35 case (JUMP_JT<<8)|JUMP_JF: 36 if (labels->labels[instr->k].location == 0xffffffff) { 37 fprintf(stderr, "Unresolved label: '%s'\n", 38 labels->labels[instr->k].label); 39 return 1; 40 } 41 instr->k = labels->labels[instr->k].location - 42 (offset + 1); 43 instr->jt = 0; 44 instr->jf = 0; 45 continue; 46 case (LABEL_JT<<8)|LABEL_JF: 47 if (labels->labels[instr->k].location != 0xffffffff) { 48 fprintf(stderr, "Duplicate label use: '%s'\n", 49 labels->labels[instr->k].label); 50 return 1; 51 } 52 labels->labels[instr->k].location = offset; 53 instr->k = 0; /* fall through */ 54 instr->jt = 0; 55 instr->jf = 0; 56 continue; 57 } 58 } 59 return 0; 60 } 61 62 /* Simple lookup table for labels. */ 63 __u32 seccomp_bpf_label(struct bpf_labels *labels, const char *label) 64 { 65 struct __bpf_label *begin = labels->labels, *end; 66 int id; 67 68 if (labels->count == BPF_LABELS_MAX) { 69 fprintf(stderr, "Too many labels\n"); 70 exit(1); 71 } 72 if (labels->count == 0) { 73 begin->label = label; 74 begin->location = 0xffffffff; 75 labels->count++; 76 return 0; 77 } 78 end = begin + labels->count; 79 for (id = 0; begin < end; ++begin, ++id) { 80 if (!strcmp(label, begin->label)) 81 return id; 82 } 83 begin->label = label; 84 begin->location = 0xffffffff; 85 labels->count++; 86 return id; 87 } 88 89 void seccomp_bpf_print(struct sock_filter *filter, size_t count) 90 { 91 struct sock_filter *end = filter + count; 92 for ( ; filter < end; ++filter) 93 printf("{ code=%u,jt=%u,jf=%u,k=%u },\n", 94 filter->code, filter->jt, filter->jf, filter->k); 95 } 96