diff options
Diffstat (limited to 'arch/arm/kernel/module-plts.c')
| -rw-r--r-- | arch/arm/kernel/module-plts.c | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c new file mode 100644 index 000000000..097e2e201 --- /dev/null +++ b/arch/arm/kernel/module-plts.c @@ -0,0 +1,183 @@ +/* + * Copyright (C) 2014 Linaro Ltd. <ard.biesheuvel@linaro.org> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#include <linux/elf.h> +#include <linux/kernel.h> +#include <linux/module.h> + +#include <asm/cache.h> +#include <asm/opcodes.h> + +#define PLT_ENT_STRIDE L1_CACHE_BYTES +#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32)) +#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT) + +#ifdef CONFIG_THUMB2_KERNEL +#define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \ + (PLT_ENT_STRIDE - 4)) +#else +#define PLT_ENT_LDR __opcode_to_mem_arm(0xe59ff000 | \ + (PLT_ENT_STRIDE - 8)) +#endif + +struct plt_entries { + u32 ldr[PLT_ENT_COUNT]; + u32 lit[PLT_ENT_COUNT]; +}; + +static bool in_init(const struct module *mod, u32 addr) +{ + return addr - (u32)mod->module_init < mod->init_size; +} + +u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val) +{ + struct plt_entries *plt, *plt_end; + int c, *count; + + if (in_init(mod, loc)) { + plt = (void *)mod->arch.init_plt->sh_addr; + plt_end = (void *)plt + mod->arch.init_plt->sh_size; + count = &mod->arch.init_plt_count; + } else { + plt = (void *)mod->arch.core_plt->sh_addr; + plt_end = (void *)plt + mod->arch.core_plt->sh_size; + count = &mod->arch.core_plt_count; + } + + /* Look for an existing entry pointing to 'val' */ + for (c = *count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) { + int i; + + if (!c) { + /* Populate a new set of entries */ + *plt = (struct plt_entries){ + { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, }, + { val, } + }; + ++*count; + return (u32)plt->ldr; + } + for (i = 0; i < PLT_ENT_COUNT; i++) { + if (!plt->lit[i]) { + plt->lit[i] = val; + ++*count; + } + if (plt->lit[i] == val) + return (u32)&plt->ldr[i]; + } + } + BUG(); +} + +static int duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num, + u32 mask) +{ + u32 *loc1, *loc2; + int i; + + for (i = 0; i < num; i++) { + if (rel[i].r_info != rel[num].r_info) + continue; + + /* + * Identical relocation types against identical symbols can + * still result in different PLT entries if the addend in the + * place is different. So resolve the target of the relocation + * to compare the values. + */ + loc1 = (u32 *)(base + rel[i].r_offset); + loc2 = (u32 *)(base + rel[num].r_offset); + if (((*loc1 ^ *loc2) & mask) == 0) + return 1; + } + return 0; +} + +/* Count how many PLT entries we may need */ +static unsigned int count_plts(Elf32_Addr base, const Elf32_Rel *rel, int num) +{ + unsigned int ret = 0; + int i; + + /* + * Sure, this is order(n^2), but it's usually short, and not + * time critical + */ + for (i = 0; i < num; i++) + switch (ELF32_R_TYPE(rel[i].r_info)) { + case R_ARM_CALL: + case R_ARM_PC24: + case R_ARM_JUMP24: + if (!duplicate_rel(base, rel, i, + __opcode_to_mem_arm(0x00ffffff))) + ret++; + break; +#ifdef CONFIG_THUMB2_KERNEL + case R_ARM_THM_CALL: + case R_ARM_THM_JUMP24: + if (!duplicate_rel(base, rel, i, + __opcode_to_mem_thumb32(0x07ff2fff))) + ret++; +#endif + } + return ret; +} + +int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, + char *secstrings, struct module *mod) +{ + unsigned long core_plts = 0, init_plts = 0; + Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum; + + /* + * To store the PLTs, we expand the .text section for core module code + * and the .init.text section for initialization code. + */ + for (s = sechdrs; s < sechdrs_end; ++s) + if (strcmp(".core.plt", secstrings + s->sh_name) == 0) + mod->arch.core_plt = s; + else if (strcmp(".init.plt", secstrings + s->sh_name) == 0) + mod->arch.init_plt = s; + + if (!mod->arch.core_plt || !mod->arch.init_plt) { + pr_err("%s: sections missing\n", mod->name); + return -ENOEXEC; + } + + for (s = sechdrs + 1; s < sechdrs_end; ++s) { + const Elf32_Rel *rels = (void *)ehdr + s->sh_offset; + int numrels = s->sh_size / sizeof(Elf32_Rel); + Elf32_Shdr *dstsec = sechdrs + s->sh_info; + + if (s->sh_type != SHT_REL) + continue; + + if (strstr(secstrings + s->sh_name, ".init")) + init_plts += count_plts(dstsec->sh_addr, rels, numrels); + else + core_plts += count_plts(dstsec->sh_addr, rels, numrels); + } + + mod->arch.core_plt->sh_type = SHT_NOBITS; + mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES; + mod->arch.core_plt->sh_size = round_up(core_plts * PLT_ENT_SIZE, + sizeof(struct plt_entries)); + mod->arch.core_plt_count = 0; + + mod->arch.init_plt->sh_type = SHT_NOBITS; + mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC; + mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES; + mod->arch.init_plt->sh_size = round_up(init_plts * PLT_ENT_SIZE, + sizeof(struct plt_entries)); + mod->arch.init_plt_count = 0; + pr_debug("%s: core.plt=%x, init.plt=%x\n", __func__, + mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size); + return 0; +} |