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| 1 | /* load shared from memory, sort of (x) 2021 by [email protected] / https://twitter.com/vx_herm1t */ | |
| 2 | #include <stdio.h> | |
| 3 | #include <stdint.h> | |
| 4 | #include <stdlib.h> | |
| 5 | #include <string.h> | |
| 6 | #include <sys/mman.h> | |
| 7 | #include <unistd.h> | |
| 8 | #include <elf.h> | |
| 9 | #include <assert.h> | |
| 10 | #include <link.h> | |
| 11 | #include <fcntl.h> | |
| 12 | ||
| 13 | static int load(unsigned char *lib, int size) | |
| 14 | {
| |
| 15 | uint8_t *map; | |
| 16 | Elf64_Ehdr *ehdr = (Elf64_Ehdr*)lib; | |
| 17 | Elf64_Phdr *phdr = (Elf64_Phdr*)(lib + ehdr->e_phoff); | |
| 18 | Elf64_Addr lo = ~0, hi = 0, t; | |
| 19 | int i; | |
| 20 | struct elf {
| |
| 21 | int relent, relpltsz, symcnt, relasz, gnuhash; | |
| 22 | char *dynstr; | |
| 23 | Elf64_Sym * dynsym; | |
| 24 | void *relplt, *rela; | |
| 25 | void *delta; | |
| 26 | void (*init)(void); | |
| 27 | uint32_t *hash; | |
| 28 | } lm, lc; | |
| 29 | bzero(&lm, sizeof(lm)); | |
| 30 | bzero(&lc, sizeof(lc)); | |
| 31 | ||
| 32 | /* get ELF size */ | |
| 33 | for (i = 0; i < ehdr->e_phnum; i++) | |
| 34 | if (phdr[i].p_type == PT_LOAD) {
| |
| 35 | if (phdr[i].p_vaddr < lo) | |
| 36 | lo = phdr[i].p_vaddr; | |
| 37 | t = phdr[i].p_vaddr + phdr[i].p_memsz; | |
| 38 | if (t > hi) | |
| 39 | hi = t; | |
| 40 | } | |
| 41 | ||
| 42 | /* allocate memory */ | |
| 43 | map = mmap(NULL, hi - lo, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); | |
| 44 | if (map == MAP_FAILED) {
| |
| 45 | printf("failed to allocate memory\n");
| |
| 46 | return 2; | |
| 47 | } | |
| 48 | ||
| 49 | /* copy segments and find DYNAMIC */ | |
| 50 | Elf64_Dyn *dyn = NULL; | |
| 51 | int f2p(int f) {
| |
| 52 | int p = PROT_READ; | |
| 53 | if (f & PF_X) | |
| 54 | p |= PROT_EXEC; | |
| 55 | if (f & PF_W) | |
| 56 | p |= PROT_WRITE; | |
| 57 | return p; | |
| 58 | } | |
| 59 | for (i = 0; i < ehdr->e_phnum; i++) {
| |
| 60 | if (phdr[i].p_type == PT_LOAD) {
| |
| 61 | if (phdr[i].p_offset == 0) | |
| 62 | lm.delta = map - lo; | |
| 63 | Elf64_Addr off = phdr[i].p_vaddr & 4095ULL; | |
| 64 | void *seg = phdr[i].p_vaddr - off + lm.delta; | |
| 65 | memcpy(seg + off, lib + phdr[i].p_offset, phdr[i].p_filesz); | |
| 66 | mprotect(seg, phdr[i].p_memsz + off, f2p(phdr[i].p_flags)); | |
| 67 | } | |
| 68 | if (phdr[i].p_type == PT_DYNAMIC) | |
| 69 | dyn = (Elf64_Dyn*)(lm.delta + phdr[i].p_vaddr); | |
| 70 | } | |
| 71 | assert(dyn != NULL); | |
| 72 | ||
| 73 | /* get init(), relocations and symbols */ | |
| 74 | void parse_dyn(Elf64_Dyn *dyn, struct elf *elf) {
| |
| 75 | #define GET_PTR(tag, var) if (dyn->d_tag == tag) elf->var = (void*)(dyn->d_un.d_val + elf->delta); | |
| 76 | #define GET_VAL(tag, var) if (dyn->d_tag == tag) elf->var = dyn->d_un.d_val; | |
| 77 | for ( ; dyn->d_tag != DT_NULL; dyn++) {
| |
| 78 | GET_PTR(DT_INIT, init) | |
| 79 | GET_PTR(DT_JMPREL, relplt) | |
| 80 | GET_VAL(DT_RELENT, relent) | |
| 81 | GET_VAL(DT_RELAENT, relent) | |
| 82 | GET_VAL(DT_PLTRELSZ, relpltsz) | |
| 83 | GET_PTR(DT_REL, rela) | |
| 84 | GET_PTR(DT_RELA, rela) | |
| 85 | GET_VAL(DT_RELSZ, relasz) | |
| 86 | GET_VAL(DT_RELASZ, relasz) | |
| 87 | GET_PTR(DT_SYMTAB, dynsym) | |
| 88 | GET_PTR(DT_STRTAB, dynstr) | |
| 89 | GET_PTR(DT_HASH, hash) | |
| 90 | GET_PTR(DT_GNU_HASH, hash) | |
| 91 | if (dyn->d_tag == DT_GNU_HASH) | |
| 92 | elf->gnuhash = 1; | |
| 93 | } | |
| 94 | /* get symbol count */ | |
| 95 | uint32_t *hash = elf->hash; | |
| 96 | if (elf->gnuhash) {
| |
| 97 | int i; | |
| 98 | uint32_t nbucket = hash[0]; | |
| 99 | uint32_t base = hash[1]; | |
| 100 | uint32_t bloom_size = hash[2]; | |
| 101 | uint64_t *bloom = (void*)&hash[4]; | |
| 102 | uint32_t *bucket = (void*)&bloom[bloom_size]; | |
| 103 | uint32_t *chain = &bucket[nbucket]; | |
| 104 | unsigned int last_sym = 0; | |
| 105 | for (i = 0; i < nbucket; i++) | |
| 106 | if (bucket[i] > last_sym) | |
| 107 | last_sym = bucket[i]; | |
| 108 | for (i = last_sym - base; !(chain[i] & 1); i++) | |
| 109 | last_sym++; | |
| 110 | elf->symcnt= last_sym + 1; | |
| 111 | } else | |
| 112 | if (hash) {
| |
| 113 | elf->symcnt = hash[1]; | |
| 114 | } else {
| |
| 115 | /* it's outdated, but... */ | |
| 116 | elf->symcnt = (elf->dynstr - (char*)elf->dynsym) / sizeof(Elf64_Sym); | |
| 117 | } | |
| 118 | } | |
| 119 | parse_dyn(dyn, &lm); | |
| 120 | ||
| 121 | /* find libc */ | |
| 122 | struct link_map *l = _r_debug.r_map; | |
| 123 | for ( ; l != NULL; l = l->l_next) | |
| 124 | if (l->l_name && *l->l_name && strstr(l->l_name, "libc")) {
| |
| 125 | printf("Found %s %p\n", l->l_name, l->l_ld);
| |
| 126 | parse_dyn(l->l_ld, &lc); | |
| 127 | lc.delta = (void*)l->l_addr; | |
| 128 | break; | |
| 129 | } | |
| 130 | assert(lc.dynsym != NULL); | |
| 131 | ||
| 132 | /* relocate, sort of */ | |
| 133 | void relocate(void *rela, int relasz, int relaent) {
| |
| 134 | void *r; | |
| 135 | for (r = rela; (r - rela) < relasz; r += relaent) {
| |
| 136 | Elf64_Rela *rela = (Elf64_Rela*)r; | |
| 137 | int index = ELF64_R_SYM(rela->r_info); | |
| 138 | void *value = 0; | |
| 139 | char *name = NULL; | |
| 140 | if (index) {
| |
| 141 | if (lm.dynsym[index].st_value) {
| |
| 142 | value = lm.dynsym[index].st_value + lm.delta; | |
| 143 | } else {
| |
| 144 | /* FIXME: use hash, search all libraries */ | |
| 145 | int found = 0; | |
| 146 | name = lm.dynsym[index].st_name + lm.dynstr; | |
| 147 | for (i = 0; i < lc.symcnt; i++) | |
| 148 | if (! strcmp(name, lc.dynsym[i].st_name + lc.dynstr)) {
| |
| 149 | value = lc.dynsym[i].st_value + lc.delta; | |
| 150 | found = 1; | |
| 151 | } | |
| 152 | if (! found) | |
| 153 | printf("Failed to resolve %d %s\n", index, name);
| |
| 154 | } | |
| 155 | } | |
| 156 | if (lm.relent == sizeof(Elf64_Rela)) | |
| 157 | value += rela->r_addend; | |
| 158 | printf("%p (%s + %x) %p\n", rela->r_offset, name ? name : "",
| |
| 159 | rela->r_addend, value - lm.delta); | |
| 160 | *(void**)(rela->r_offset + lm.delta) = value; | |
| 161 | } | |
| 162 | } | |
| 163 | relocate(lm.relplt, lm.relpltsz, lm.relent); | |
| 164 | relocate(lm.rela, lm.relasz, lm.relent); | |
| 165 | ||
| 166 | printf("Done! Call init\n");
| |
| 167 | if (lm.init) | |
| 168 | lm.init(); | |
| 169 | } | |
| 170 | ||
| 171 | int main(int argc, char **argv) | |
| 172 | {
| |
| 173 | int h = open(argv[1], 0); | |
| 174 | int l = lseek(h, 0, 2); | |
| 175 | lseek(h, 0, 0); | |
| 176 | unsigned char lib[l]; | |
| 177 | if (h > 0 && l > 0 && read(h, lib, l) == l) | |
| 178 | load(lib, l); | |
| 179 | else | |
| 180 | printf("Failed to read %s\n", argv[1]);
| |
| 181 | close(h); | |
| 182 | return 0; | |
| 183 | } |
