1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org> 4 */ 5 6 #include <linux/elf.h> 7 #include <linux/ftrace.h> 8 #include <linux/kernel.h> 9 #include <linux/module.h> 10 #include <linux/moduleloader.h> 11 #include <linux/sort.h> 12 13 static struct plt_entry __get_adrp_add_pair(u64 dst, u64 pc, 14 enum aarch64_insn_register reg) 15 { 16 u32 adrp, add; 17 18 adrp = aarch64_insn_gen_adr(pc, dst, reg, AARCH64_INSN_ADR_TYPE_ADRP); 19 add = aarch64_insn_gen_add_sub_imm(reg, reg, dst % SZ_4K, 20 AARCH64_INSN_VARIANT_64BIT, 21 AARCH64_INSN_ADSB_ADD); 22 23 return (struct plt_entry){ cpu_to_le32(adrp), cpu_to_le32(add) }; 24 } 25 26 struct plt_entry get_plt_entry(u64 dst, void *pc) 27 { 28 struct plt_entry plt; 29 static u32 br; 30 31 if (!br) 32 br = aarch64_insn_gen_branch_reg(AARCH64_INSN_REG_16, 33 AARCH64_INSN_BRANCH_NOLINK); 34 35 plt = __get_adrp_add_pair(dst, (u64)pc, AARCH64_INSN_REG_16); 36 plt.br = cpu_to_le32(br); 37 38 return plt; 39 } 40 41 static bool plt_entries_equal(const struct plt_entry *a, 42 const struct plt_entry *b) 43 { 44 u64 p, q; 45 46 /* 47 * Check whether both entries refer to the same target: 48 * do the cheapest checks first. 49 * If the 'add' or 'br' opcodes are different, then the target 50 * cannot be the same. 51 */ 52 if (a->add != b->add || a->br != b->br) 53 return false; 54 55 p = ALIGN_DOWN((u64)a, SZ_4K); 56 q = ALIGN_DOWN((u64)b, SZ_4K); 57 58 /* 59 * If the 'adrp' opcodes are the same then we just need to check 60 * that they refer to the same 4k region. 61 */ 62 if (a->adrp == b->adrp && p == q) 63 return true; 64 65 return (p + aarch64_insn_adrp_get_offset(le32_to_cpu(a->adrp))) == 66 (q + aarch64_insn_adrp_get_offset(le32_to_cpu(b->adrp))); 67 } 68 69 u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs, 70 void *loc, const Elf64_Rela *rela, 71 Elf64_Sym *sym) 72 { 73 struct mod_plt_sec *pltsec = !within_module_init((unsigned long)loc, mod) ? 74 &mod->arch.core : &mod->arch.init; 75 struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr; 76 int i = pltsec->plt_num_entries; 77 int j = i - 1; 78 u64 val = sym->st_value + rela->r_addend; 79 80 if (is_forbidden_offset_for_adrp(&plt[i].adrp)) 81 i++; 82 83 plt[i] = get_plt_entry(val, &plt[i]); 84 85 /* 86 * Check if the entry we just created is a duplicate. Given that the 87 * relocations are sorted, this will be the last entry we allocated. 88 * (if one exists). 89 */ 90 if (j >= 0 && plt_entries_equal(plt + i, plt + j)) 91 return (u64)&plt[j]; 92 93 pltsec->plt_num_entries += i - j; 94 if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries)) 95 return 0; 96 97 return (u64)&plt[i]; 98 } 99 100 #ifdef CONFIG_ARM64_ERRATUM_843419 101 u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs, 102 void *loc, u64 val) 103 { 104 struct mod_plt_sec *pltsec = !within_module_init((unsigned long)loc, mod) ? 105 &mod->arch.core : &mod->arch.init; 106 struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr; 107 int i = pltsec->plt_num_entries++; 108 u32 br; 109 int rd; 110 111 if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries)) 112 return 0; 113 114 if (is_forbidden_offset_for_adrp(&plt[i].adrp)) 115 i = pltsec->plt_num_entries++; 116 117 /* get the destination register of the ADRP instruction */ 118 rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD, 119 le32_to_cpup((__le32 *)loc)); 120 121 br = aarch64_insn_gen_branch_imm((u64)&plt[i].br, (u64)loc + 4, 122 AARCH64_INSN_BRANCH_NOLINK); 123 124 plt[i] = __get_adrp_add_pair(val, (u64)&plt[i], rd); 125 plt[i].br = cpu_to_le32(br); 126 127 return (u64)&plt[i]; 128 } 129 #endif 130 131 #define cmp_3way(a, b) ((a) < (b) ? -1 : (a) > (b)) 132 133 static int cmp_rela(const void *a, const void *b) 134 { 135 const Elf64_Rela *x = a, *y = b; 136 int i; 137 138 /* sort by type, symbol index and addend */ 139 i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info)); 140 if (i == 0) 141 i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info)); 142 if (i == 0) 143 i = cmp_3way(x->r_addend, y->r_addend); 144 return i; 145 } 146 147 static bool duplicate_rel(const Elf64_Rela *rela, int num) 148 { 149 /* 150 * Entries are sorted by type, symbol index and addend. That means 151 * that, if a duplicate entry exists, it must be in the preceding 152 * slot. 153 */ 154 return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0; 155 } 156 157 static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num, 158 Elf64_Word dstidx, Elf_Shdr *dstsec) 159 { 160 unsigned int ret = 0; 161 Elf64_Sym *s; 162 int i; 163 164 for (i = 0; i < num; i++) { 165 u64 min_align; 166 167 switch (ELF64_R_TYPE(rela[i].r_info)) { 168 case R_AARCH64_JUMP26: 169 case R_AARCH64_CALL26: 170 if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) 171 break; 172 173 /* 174 * We only have to consider branch targets that resolve 175 * to symbols that are defined in a different section. 176 * This is not simply a heuristic, it is a fundamental 177 * limitation, since there is no guaranteed way to emit 178 * PLT entries sufficiently close to the branch if the 179 * section size exceeds the range of a branch 180 * instruction. So ignore relocations against defined 181 * symbols if they live in the same section as the 182 * relocation target. 183 */ 184 s = syms + ELF64_R_SYM(rela[i].r_info); 185 if (s->st_shndx == dstidx) 186 break; 187 188 /* 189 * Jump relocations with non-zero addends against 190 * undefined symbols are supported by the ELF spec, but 191 * do not occur in practice (e.g., 'jump n bytes past 192 * the entry point of undefined function symbol f'). 193 * So we need to support them, but there is no need to 194 * take them into consideration when trying to optimize 195 * this code. So let's only check for duplicates when 196 * the addend is zero: this allows us to record the PLT 197 * entry address in the symbol table itself, rather than 198 * having to search the list for duplicates each time we 199 * emit one. 200 */ 201 if (rela[i].r_addend != 0 || !duplicate_rel(rela, i)) 202 ret++; 203 break; 204 case R_AARCH64_ADR_PREL_PG_HI21_NC: 205 case R_AARCH64_ADR_PREL_PG_HI21: 206 if (!IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) || 207 !cpus_have_const_cap(ARM64_WORKAROUND_843419)) 208 break; 209 210 /* 211 * Determine the minimal safe alignment for this ADRP 212 * instruction: the section alignment at which it is 213 * guaranteed not to appear at a vulnerable offset. 214 * 215 * This comes down to finding the least significant zero 216 * bit in bits [11:3] of the section offset, and 217 * increasing the section's alignment so that the 218 * resulting address of this instruction is guaranteed 219 * to equal the offset in that particular bit (as well 220 * as all less significant bits). This ensures that the 221 * address modulo 4 KB != 0xfff8 or 0xfffc (which would 222 * have all ones in bits [11:3]) 223 */ 224 min_align = 2ULL << ffz(rela[i].r_offset | 0x7); 225 226 /* 227 * Allocate veneer space for each ADRP that may appear 228 * at a vulnerable offset nonetheless. At relocation 229 * time, some of these will remain unused since some 230 * ADRP instructions can be patched to ADR instructions 231 * instead. 232 */ 233 if (min_align > SZ_4K) 234 ret++; 235 else 236 dstsec->sh_addralign = max(dstsec->sh_addralign, 237 min_align); 238 break; 239 } 240 } 241 242 if (IS_ENABLED(CONFIG_ARM64_ERRATUM_843419) && 243 cpus_have_const_cap(ARM64_WORKAROUND_843419)) 244 /* 245 * Add some slack so we can skip PLT slots that may trigger 246 * the erratum due to the placement of the ADRP instruction. 247 */ 248 ret += DIV_ROUND_UP(ret, (SZ_4K / sizeof(struct plt_entry))); 249 250 return ret; 251 } 252 253 static bool branch_rela_needs_plt(Elf64_Sym *syms, Elf64_Rela *rela, 254 Elf64_Word dstidx) 255 { 256 257 Elf64_Sym *s = syms + ELF64_R_SYM(rela->r_info); 258 259 if (s->st_shndx == dstidx) 260 return false; 261 262 return ELF64_R_TYPE(rela->r_info) == R_AARCH64_JUMP26 || 263 ELF64_R_TYPE(rela->r_info) == R_AARCH64_CALL26; 264 } 265 266 /* Group branch PLT relas at the front end of the array. */ 267 static int partition_branch_plt_relas(Elf64_Sym *syms, Elf64_Rela *rela, 268 int numrels, Elf64_Word dstidx) 269 { 270 int i = 0, j = numrels - 1; 271 272 if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) 273 return 0; 274 275 while (i < j) { 276 if (branch_rela_needs_plt(syms, &rela[i], dstidx)) 277 i++; 278 else if (branch_rela_needs_plt(syms, &rela[j], dstidx)) 279 swap(rela[i], rela[j]); 280 else 281 j--; 282 } 283 284 return i; 285 } 286 287 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 288 char *secstrings, struct module *mod) 289 { 290 unsigned long core_plts = 0; 291 unsigned long init_plts = 0; 292 Elf64_Sym *syms = NULL; 293 Elf_Shdr *pltsec, *tramp = NULL; 294 int i; 295 296 /* 297 * Find the empty .plt section so we can expand it to store the PLT 298 * entries. Record the symtab address as well. 299 */ 300 for (i = 0; i < ehdr->e_shnum; i++) { 301 if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt")) 302 mod->arch.core.plt_shndx = i; 303 else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) 304 mod->arch.init.plt_shndx = i; 305 else if (!strcmp(secstrings + sechdrs[i].sh_name, 306 ".text.ftrace_trampoline")) 307 tramp = sechdrs + i; 308 else if (sechdrs[i].sh_type == SHT_SYMTAB) 309 syms = (Elf64_Sym *)sechdrs[i].sh_addr; 310 } 311 312 if (!mod->arch.core.plt_shndx || !mod->arch.init.plt_shndx) { 313 pr_err("%s: module PLT section(s) missing\n", mod->name); 314 return -ENOEXEC; 315 } 316 if (!syms) { 317 pr_err("%s: module symtab section missing\n", mod->name); 318 return -ENOEXEC; 319 } 320 321 for (i = 0; i < ehdr->e_shnum; i++) { 322 Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset; 323 int nents, numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela); 324 Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info; 325 326 if (sechdrs[i].sh_type != SHT_RELA) 327 continue; 328 329 /* ignore relocations that operate on non-exec sections */ 330 if (!(dstsec->sh_flags & SHF_EXECINSTR)) 331 continue; 332 333 /* 334 * sort branch relocations requiring a PLT by type, symbol index 335 * and addend 336 */ 337 nents = partition_branch_plt_relas(syms, rels, numrels, 338 sechdrs[i].sh_info); 339 if (nents) 340 sort(rels, nents, sizeof(Elf64_Rela), cmp_rela, NULL); 341 342 if (!module_init_layout_section(secstrings + dstsec->sh_name)) 343 core_plts += count_plts(syms, rels, numrels, 344 sechdrs[i].sh_info, dstsec); 345 else 346 init_plts += count_plts(syms, rels, numrels, 347 sechdrs[i].sh_info, dstsec); 348 } 349 350 pltsec = sechdrs + mod->arch.core.plt_shndx; 351 pltsec->sh_type = SHT_NOBITS; 352 pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 353 pltsec->sh_addralign = L1_CACHE_BYTES; 354 pltsec->sh_size = (core_plts + 1) * sizeof(struct plt_entry); 355 mod->arch.core.plt_num_entries = 0; 356 mod->arch.core.plt_max_entries = core_plts; 357 358 pltsec = sechdrs + mod->arch.init.plt_shndx; 359 pltsec->sh_type = SHT_NOBITS; 360 pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 361 pltsec->sh_addralign = L1_CACHE_BYTES; 362 pltsec->sh_size = (init_plts + 1) * sizeof(struct plt_entry); 363 mod->arch.init.plt_num_entries = 0; 364 mod->arch.init.plt_max_entries = init_plts; 365 366 if (tramp) { 367 tramp->sh_type = SHT_NOBITS; 368 tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 369 tramp->sh_addralign = __alignof__(struct plt_entry); 370 tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry); 371 } 372 373 return 0; 374 } 375