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/sort.h> 11 #include <linux/moduleloader.h> 12 13 #include <asm/cache.h> 14 #include <asm/opcodes.h> 15 16 #ifdef CONFIG_THUMB2_KERNEL 17 #define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \ 18 (PLT_ENT_STRIDE - 4)) 19 #else 20 #define PLT_ENT_LDR __opcode_to_mem_arm(0xe59ff000 | \ 21 (PLT_ENT_STRIDE - 8)) 22 #endif 23 24 static const u32 fixed_plts[] = { 25 #ifdef CONFIG_DYNAMIC_FTRACE 26 FTRACE_ADDR, 27 MCOUNT_ADDR, 28 #endif 29 }; 30 31 static void prealloc_fixed(struct mod_plt_sec *pltsec, struct plt_entries *plt) 32 { 33 int i; 34 35 if (!ARRAY_SIZE(fixed_plts) || pltsec->plt_count) 36 return; 37 pltsec->plt_count = ARRAY_SIZE(fixed_plts); 38 39 for (i = 0; i < ARRAY_SIZE(plt->ldr); ++i) 40 plt->ldr[i] = PLT_ENT_LDR; 41 42 BUILD_BUG_ON(sizeof(fixed_plts) > sizeof(plt->lit)); 43 memcpy(plt->lit, fixed_plts, sizeof(fixed_plts)); 44 } 45 46 u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val) 47 { 48 struct mod_plt_sec *pltsec = !within_module_init(loc, mod) ? 49 &mod->arch.core : &mod->arch.init; 50 struct plt_entries *plt; 51 int idx; 52 53 /* cache the address, ELF header is available only during module load */ 54 if (!pltsec->plt_ent) 55 pltsec->plt_ent = (struct plt_entries *)pltsec->plt->sh_addr; 56 plt = pltsec->plt_ent; 57 58 prealloc_fixed(pltsec, plt); 59 60 for (idx = 0; idx < ARRAY_SIZE(fixed_plts); ++idx) 61 if (plt->lit[idx] == val) 62 return (u32)&plt->ldr[idx]; 63 64 idx = 0; 65 /* 66 * Look for an existing entry pointing to 'val'. Given that the 67 * relocations are sorted, this will be the last entry we allocated. 68 * (if one exists). 69 */ 70 if (pltsec->plt_count > 0) { 71 plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT; 72 idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT; 73 74 if (plt->lit[idx] == val) 75 return (u32)&plt->ldr[idx]; 76 77 idx = (idx + 1) % PLT_ENT_COUNT; 78 if (!idx) 79 plt++; 80 } 81 82 pltsec->plt_count++; 83 BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size); 84 85 if (!idx) 86 /* Populate a new set of entries */ 87 *plt = (struct plt_entries){ 88 { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, }, 89 { val, } 90 }; 91 else 92 plt->lit[idx] = val; 93 94 return (u32)&plt->ldr[idx]; 95 } 96 97 #define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b)) 98 99 static int cmp_rel(const void *a, const void *b) 100 { 101 const Elf32_Rel *x = a, *y = b; 102 int i; 103 104 /* sort by type and symbol index */ 105 i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info)); 106 if (i == 0) 107 i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info)); 108 return i; 109 } 110 111 static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel) 112 { 113 u32 *tval = (u32 *)(base + rel->r_offset); 114 115 /* 116 * Do a bitwise compare on the raw addend rather than fully decoding 117 * the offset and doing an arithmetic comparison. 118 * Note that a zero-addend jump/call relocation is encoded taking the 119 * PC bias into account, i.e., -8 for ARM and -4 for Thumb2. 120 */ 121 switch (ELF32_R_TYPE(rel->r_info)) { 122 u16 upper, lower; 123 124 case R_ARM_THM_CALL: 125 case R_ARM_THM_JUMP24: 126 upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]); 127 lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]); 128 129 return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe; 130 131 case R_ARM_CALL: 132 case R_ARM_PC24: 133 case R_ARM_JUMP24: 134 return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe; 135 } 136 BUG(); 137 } 138 139 static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num) 140 { 141 const Elf32_Rel *prev; 142 143 /* 144 * Entries are sorted by type and symbol index. That means that, 145 * if a duplicate entry exists, it must be in the preceding 146 * slot. 147 */ 148 if (!num) 149 return false; 150 151 prev = rel + num - 1; 152 return cmp_rel(rel + num, prev) == 0 && 153 is_zero_addend_relocation(base, prev); 154 } 155 156 /* Count how many PLT entries we may need */ 157 static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base, 158 const Elf32_Rel *rel, int num, Elf32_Word dstidx) 159 { 160 unsigned int ret = 0; 161 const Elf32_Sym *s; 162 int i; 163 164 for (i = 0; i < num; i++) { 165 switch (ELF32_R_TYPE(rel[i].r_info)) { 166 case R_ARM_CALL: 167 case R_ARM_PC24: 168 case R_ARM_JUMP24: 169 case R_ARM_THM_CALL: 170 case R_ARM_THM_JUMP24: 171 /* 172 * We only have to consider branch targets that resolve 173 * to symbols that are defined in a different section. 174 * This is not simply a heuristic, it is a fundamental 175 * limitation, since there is no guaranteed way to emit 176 * PLT entries sufficiently close to the branch if the 177 * section size exceeds the range of a branch 178 * instruction. So ignore relocations against defined 179 * symbols if they live in the same section as the 180 * relocation target. 181 */ 182 s = syms + ELF32_R_SYM(rel[i].r_info); 183 if (s->st_shndx == dstidx) 184 break; 185 186 /* 187 * Jump relocations with non-zero addends against 188 * undefined symbols are supported by the ELF spec, but 189 * do not occur in practice (e.g., 'jump n bytes past 190 * the entry point of undefined function symbol f'). 191 * So we need to support them, but there is no need to 192 * take them into consideration when trying to optimize 193 * this code. So let's only check for duplicates when 194 * the addend is zero. (Note that calls into the core 195 * module via init PLT entries could involve section 196 * relative symbol references with non-zero addends, for 197 * which we may end up emitting duplicates, but the init 198 * PLT is released along with the rest of the .init 199 * region as soon as module loading completes.) 200 */ 201 if (!is_zero_addend_relocation(base, rel + i) || 202 !duplicate_rel(base, rel, i)) 203 ret++; 204 } 205 } 206 return ret; 207 } 208 209 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, 210 char *secstrings, struct module *mod) 211 { 212 unsigned long core_plts = ARRAY_SIZE(fixed_plts); 213 unsigned long init_plts = ARRAY_SIZE(fixed_plts); 214 Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum; 215 Elf32_Sym *syms = NULL; 216 217 /* 218 * To store the PLTs, we expand the .text section for core module code 219 * and for initialization code. 220 */ 221 for (s = sechdrs; s < sechdrs_end; ++s) { 222 if (strcmp(".plt", secstrings + s->sh_name) == 0) 223 mod->arch.core.plt = s; 224 else if (strcmp(".init.plt", secstrings + s->sh_name) == 0) 225 mod->arch.init.plt = s; 226 else if (s->sh_type == SHT_SYMTAB) 227 syms = (Elf32_Sym *)s->sh_addr; 228 } 229 230 if (!mod->arch.core.plt || !mod->arch.init.plt) { 231 pr_err("%s: module PLT section(s) missing\n", mod->name); 232 return -ENOEXEC; 233 } 234 if (!syms) { 235 pr_err("%s: module symtab section missing\n", mod->name); 236 return -ENOEXEC; 237 } 238 239 for (s = sechdrs + 1; s < sechdrs_end; ++s) { 240 Elf32_Rel *rels = (void *)ehdr + s->sh_offset; 241 int numrels = s->sh_size / sizeof(Elf32_Rel); 242 Elf32_Shdr *dstsec = sechdrs + s->sh_info; 243 244 if (s->sh_type != SHT_REL) 245 continue; 246 247 /* ignore relocations that operate on non-exec sections */ 248 if (!(dstsec->sh_flags & SHF_EXECINSTR)) 249 continue; 250 251 /* sort by type and symbol index */ 252 sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL); 253 254 if (!module_init_layout_section(secstrings + dstsec->sh_name)) 255 core_plts += count_plts(syms, dstsec->sh_addr, rels, 256 numrels, s->sh_info); 257 else 258 init_plts += count_plts(syms, dstsec->sh_addr, rels, 259 numrels, s->sh_info); 260 } 261 262 mod->arch.core.plt->sh_type = SHT_NOBITS; 263 mod->arch.core.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 264 mod->arch.core.plt->sh_addralign = L1_CACHE_BYTES; 265 mod->arch.core.plt->sh_size = round_up(core_plts * PLT_ENT_SIZE, 266 sizeof(struct plt_entries)); 267 mod->arch.core.plt_count = 0; 268 mod->arch.core.plt_ent = NULL; 269 270 mod->arch.init.plt->sh_type = SHT_NOBITS; 271 mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; 272 mod->arch.init.plt->sh_addralign = L1_CACHE_BYTES; 273 mod->arch.init.plt->sh_size = round_up(init_plts * PLT_ENT_SIZE, 274 sizeof(struct plt_entries)); 275 mod->arch.init.plt_count = 0; 276 mod->arch.init.plt_ent = NULL; 277 278 pr_debug("%s: plt=%x, init.plt=%x\n", __func__, 279 mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size); 280 return 0; 281 } 282 283 bool in_module_plt(unsigned long loc) 284 { 285 struct module *mod; 286 bool ret; 287 288 preempt_disable(); 289 mod = __module_text_address(loc); 290 ret = mod && (loc - (u32)mod->arch.core.plt_ent < mod->arch.core.plt_count * PLT_ENT_SIZE || 291 loc - (u32)mod->arch.init.plt_ent < mod->arch.init.plt_count * PLT_ENT_SIZE); 292 preempt_enable(); 293 294 return ret; 295 } 296