LXR linux/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
  28struct plt_entries {
  29        u32     ldr[PLT_ENT_COUNT];
  30        u32     lit[PLT_ENT_COUNT];
  31};
  32
  33static bool in_init(const struct module *mod, u32 addr)
  34{
  35        return addr - (u32)mod->init_layout.base < mod->init_layout.size;
  36}
  37
  38u32 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
  78static 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 */
 103static 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
 132int 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}
 184