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