1 /* 2 * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org> 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License version 2 as 6 * published by the Free Software Foundation. 7 */ 8 9 #include <linux/elf.h> 10 #include <linux/kernel.h> 11 #include <linux/module.h> 12 #include <linux/sort.h> 13 14 static bool in_init(const struct module *mod, void *loc) 15 { 16 return (u64)loc - (u64)mod->init_layout.base < mod->init_layout.size; 17 } 18 19 u64 module_emit_plt_entry(struct module *mod, void *loc, const Elf64_Rela *rela, 20 Elf64_Sym *sym) 21 { 22 struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core : 23 &mod->arch.init; 24 struct plt_entry *plt = (struct plt_entry *)pltsec->plt->sh_addr; 25 int i = pltsec->plt_num_entries; 26 u64 val = sym->st_value + rela->r_addend; 27 28 plt[i] = get_plt_entry(val); 29 30 /* 31 * Check if the entry we just created is a duplicate. Given that the 32 * relocations are sorted, this will be the last entry we allocated. 33 * (if one exists). 34 */ 35 if (i > 0 && plt_entries_equal(plt + i, plt + i - 1)) 36 return (u64)&plt[i - 1]; 37 38 pltsec->plt_num_entries++; 39 if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries)) 40 return 0; 41 42 return (u64)&plt[i]; 43 } 44 45 #define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b)) 46 47 static int cmp_rela(const void *a, const void *b) 48 { 49 const Elf64_Rela *x = a, *y = b; 50 int i; 51 52 /* sort by type, symbol index and addend */ 53 i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info)); 54 if (i == 0) 55 i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info)); 56 if (i == 0) 57 i = cmp_3way(x->r_addend, y->r_addend); 58 return i; 59 } 60 61 static bool duplicate_rel(const Elf64_Rela *rela, int num) 62 { 63 /* 64 * Entries are sorted by type, symbol index and addend. That means 65 * that, if a duplicate entry exists, it must be in the preceding 66 * slot. 67 */ 68 return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0; 69 } 70 71 static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num, 72 Elf64_Word dstidx) 73 { 74 unsigned int ret = 0; 75 Elf64_Sym *s; 76 int i; 77 78 for (i = 0; i < num; i++) { 79 switch (ELF64_R_TYPE(rela[i].r_info)) { 80 case R_AARCH64_JUMP26: 81 case R_AARCH64_CALL26: 82 /* 83 * We only have to consider branch targets that resolve 84 * to symbols that are defined in a different section. 85 * This is not simply a heuristic, it is a fundamental 86 * limitation, since there is no guaranteed way to emit 87 * PLT entries sufficiently close to the branch if the 88 * section size exceeds the range of a branch 89 * instruction. So ignore relocations against defined 90 * symbols if they live in the same section as the 91 * relocation target. 92 */ 93 s = syms + ELF64_R_SYM(rela[i].r_info); 94 if (s->st_shndx == dstidx) 95 break; 96 97 /* 98 * Jump relocations with non-zero addends against 99 * undefined symbols are supported by the ELF spec, but 100 * do not occur in practice (e.g., 'jump n bytes past 101 * the entry point of undefined function symbol f'). 102 * So we need to support them, but there is no need to 103 * take them into consideration when trying to optimize 104 * this code. So let's only check for duplicates when 105 * the addend is zero: this allows us to record the PLT 106 * entry address in the symbol table itself, rather than 107 * having to search the list for duplicates each time we 108 * emit one. 109 */ 110 if (rela[i].r_addend != 0 || !duplicate_rel(rela, i)) 111 ret++; 112 break; 113 } 114 } 115 return ret; 116 } 117 118 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 119 char *secstrings, struct module *mod) 120 { 121 unsigned long core_plts = 0; 122 unsigned long init_plts = 0; 123 Elf64_Sym *syms = NULL; 124 Elf_Shdr *tramp = NULL; 125 int i; 126 127 /* 128 * Find the empty .plt section so we can expand it to store the PLT 129 * entries. Record the symtab address as well. 130 */ 131 for (i = 0; i < ehdr->e_shnum; i++) { 132 if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt")) 133 mod->arch.core.plt = sechdrs + i; 134 else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) 135 mod->arch.init.plt = sechdrs + i; 136 else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && 137 !strcmp(secstrings + sechdrs[i].sh_name, 138 ".text.ftrace_trampoline")) 139 tramp = sechdrs + i; 140 else if (sechdrs[i].sh_type == SHT_SYMTAB) 141 syms = (Elf64_Sym *)sechdrs[i].sh_addr; 142 } 143 144 if (!mod->arch.core.plt || !mod->arch.init.plt) { 145 pr_err("%s: module PLT section(s) missing\n", mod->name); 146 return -ENOEXEC; 147 } 148 if (!syms) { 149 pr_err("%s: module symtab section missing\n", mod->name); 150 return -ENOEXEC; 151 } 152 153 for (i = 0; i < ehdr->e_shnum; i++) { 154 Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; 155 int numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); 156 Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info; 157 158 if (sechdrs[i].sh_type != SHT_RELA) 159 continue; 160 161 /* ignore relocations that operate on non-exec sections */ 162 if (!(dstsec->sh_flags & SHF_EXECINSTR)) 163 continue; 164 165 /* sort by type, symbol index and addend */ 166 sort(rels, numrels, sizeof(Elf64_Rela), cmp_rela, NULL); 167 168 if (strncmp(secstrings + dstsec->sh_name, ".init", 5) != 0) 169 core_plts += count_plts(syms, rels, numrels, 170 sechdrs[i].sh_info); 171 else 172 init_plts += count_plts(syms, rels, numrels, 173 sechdrs[i].sh_info); 174 } 175 176 mod->arch.core.plt->sh_type = SHT_NOBITS; 177 mod->arch.core.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 178 mod->arch.core.plt->sh_addralign = L1_CACHE_BYTES; 179 mod->arch.core.plt->sh_size = (core_plts + 1) * sizeof(struct plt_entry); 180 mod->arch.core.plt_num_entries = 0; 181 mod->arch.core.plt_max_entries = core_plts; 182 183 mod->arch.init.plt->sh_type = SHT_NOBITS; 184 mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 185 mod->arch.init.plt->sh_addralign = L1_CACHE_BYTES; 186 mod->arch.init.plt->sh_size = (init_plts + 1) * sizeof(struct plt_entry); 187 mod->arch.init.plt_num_entries = 0; 188 mod->arch.init.plt_max_entries = init_plts; 189 190 if (tramp) { 191 tramp->sh_type = SHT_NOBITS; 192 tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 193 tramp->sh_addralign = __alignof__(struct plt_entry); 194 tramp->sh_size = sizeof(struct plt_entry); 195 } 196 197 return 0; 198 } 199