arch/arm/kernel/module-plts.c

   1 /*
   2  * Copyright (C) 2014 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
  13 #include <asm/cache.h>
  14 #include <asm/opcodes.h>
  15
  16 #define PLT_ENT_STRIDE          L1_CACHE_BYTES
  17 #define PLT_ENT_COUNT           (PLT_ENT_STRIDE / sizeof(u32))
  18 #define PLT_ENT_SIZE            (sizeof(struct plt_entries) / PLT_ENT_COUNT)
  19
  20 #ifdef CONFIG_THUMB2_KERNEL
  21 #define PLT_ENT_LDR             __opcode_to_mem_thumb32(0xf8dff000 | \
  22                                                         (PLT_ENT_STRIDE - 4))
  23 #else
  24 #define PLT_ENT_LDR             __opcode_to_mem_arm(0xe59ff000 | \
  25                                                     (PLT_ENT_STRIDE - 8))
  26 #endif
  27
  28 struct plt_entries {
  29         u32     ldr[PLT_ENT_COUNT];
  30         u32     lit[PLT_ENT_COUNT];
  31 };
  32
  33 static bool in_init(const struct module *mod, u32 addr)
  34 {
  35         return addr - (u32)mod->module_init < mod->init_size;
  36 }
  37
  38 u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
  39 {
  40         struct plt_entries *plt, *plt_end;
  41         int c, *count;
  42
  43         if (in_init(mod, loc)) {
  44                 plt = (void *)mod->arch.init_plt->sh_addr;
  45                 plt_end = (void *)plt + mod->arch.init_plt->sh_size;
  46                 count = &mod->arch.init_plt_count;
  47         } else {
  48                 plt = (void *)mod->arch.core_plt->sh_addr;
  49                 plt_end = (void *)plt + mod->arch.core_plt->sh_size;
  50                 count = &mod->arch.core_plt_count;
  51         }
  52
  53         /* Look for an existing entry pointing to 'val' */
  54         for (c = *count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) {
  55                 int i;
  56
  57                 if (!c) {
  58                         /* Populate a new set of entries */
  59                         *plt = (struct plt_entries){
  60                                 { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
  61                                 { val, }
  62                         };
  63                         ++*count;
  64                         return (u32)plt->ldr;
  65                 }
  66                 for (i = 0; i < PLT_ENT_COUNT; i++) {
  67                         if (!plt->lit[i]) {
  68                                 plt->lit[i] = val;
  69                                 ++*count;
  70                         }
  71                         if (plt->lit[i] == val)
  72                                 return (u32)&plt->ldr[i];
  73                 }
  74         }
  75         BUG();
  76 }
  77
  78 static int duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num,
  79                            u32 mask)
  80 {
  81         u32 *loc1, *loc2;
  82         int i;
  83
  84         for (i = 0; i < num; i++) {
  85                 if (rel[i].r_info != rel[num].r_info)
  86                         continue;
  87
  88                 /*
  89                  * Identical relocation types against identical symbols can
  90                  * still result in different PLT entries if the addend in the
  91                  * place is different. So resolve the target of the relocation
  92                  * to compare the values.
  93                  */
  94                 loc1 = (u32 *)(base + rel[i].r_offset);
  95                 loc2 = (u32 *)(base + rel[num].r_offset);
  96                 if (((*loc1 ^ *loc2) & mask) == 0)
  97                         return 1;
  98         }
  99         return 0;
 100 }
 101
 102 /* Count how many PLT entries we may need */
 103 static unsigned int count_plts(Elf32_Addr base, const Elf32_Rel *rel, int num)
 104 {
 105         unsigned int ret = 0;
 106         int i;
 107
 108         /*
 109          * Sure, this is order(n^2), but it's usually short, and not
 110          * time critical
 111          */
 112         for (i = 0; i < num; i++)
 113                 switch (ELF32_R_TYPE(rel[i].r_info)) {
 114                 case R_ARM_CALL:
 115                 case R_ARM_PC24:
 116                 case R_ARM_JUMP24:
 117                         if (!duplicate_rel(base, rel, i,
 118                                            __opcode_to_mem_arm(0x00ffffff)))
 119                                 ret++;
 120                         break;
 121 #ifdef CONFIG_THUMB2_KERNEL
 122                 case R_ARM_THM_CALL:
 123                 case R_ARM_THM_JUMP24:
 124                         if (!duplicate_rel(base, rel, i,
 125                                            __opcode_to_mem_thumb32(0x07ff2fff)))
 126                                 ret++;
 127 #endif
 128                 }
 129         return ret;
 130 }
 131
 132 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
 133                               char *secstrings, struct module *mod)
 134 {
 135         unsigned long core_plts = 0, init_plts = 0;
 136         Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
 137
 138         /*
 139          * To store the PLTs, we expand the .text section for core module code
 140          * and the .init.text section for initialization code.
 141          */
 142         for (s = sechdrs; s < sechdrs_end; ++s)
 143                 if (strcmp(".core.plt", secstrings + s->sh_name) == 0)
 144                         mod->arch.core_plt = s;
 145                 else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
 146                         mod->arch.init_plt = s;
 147
 148         if (!mod->arch.core_plt || !mod->arch.init_plt) {
 149                 pr_err("%s: sections missing\n", mod->name);
 150                 return -ENOEXEC;
 151         }
 152
 153         for (s = sechdrs + 1; s < sechdrs_end; ++s) {
 154                 const Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
 155                 int numrels = s->sh_size / sizeof(Elf32_Rel);
 156                 Elf32_Shdr *dstsec = sechdrs + s->sh_info;
 157
 158                 if (s->sh_type != SHT_REL)
 159                         continue;
 160
 161                 if (strstr(secstrings + s->sh_name, ".init"))
 162                         init_plts += count_plts(dstsec->sh_addr, rels, numrels);
 163                 else
 164                         core_plts += count_plts(dstsec->sh_addr, rels, numrels);
 165         }
 166
 167         mod->arch.core_plt->sh_type = SHT_NOBITS;
 168         mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
 169         mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES;
 170         mod->arch.core_plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
 171                                                sizeof(struct plt_entries));
 172         mod->arch.core_plt_count = 0;
 173
 174         mod->arch.init_plt->sh_type = SHT_NOBITS;
 175         mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
 176         mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES;
 177         mod->arch.init_plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
 178                                                sizeof(struct plt_entries));
 179         mod->arch.init_plt_count = 0;
 180         pr_debug("%s: core.plt=%x, init.plt=%x\n", __func__,
 181                  mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size);
 182         return 0;
 183 }