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/*
* 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];
};
u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
struct plt_entries *plt, *plt_end;
int c;
plt = (void *)mod->arch.plt->sh_addr;
plt_end = (void *)plt + mod->arch.plt->sh_size;
/* Look for an existing entry pointing to 'val' */
for (c = mod->arch.plt_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, }
};
mod->arch.plt_count++;
return (u32)plt->ldr;
}
for (i = 0; i < PLT_ENT_COUNT; i++) {
if (!plt->lit[i]) {
plt->lit[i] = val;
mod->arch.plt_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(const Elf32_Sym *syms, Elf32_Addr base,
const Elf32_Rel *rel, int num)
{
unsigned int ret = 0;
const Elf32_Sym *s;
u32 mask;
int i;
if (IS_ENABLED(CONFIG_THUMB2_KERNEL))
mask = __opcode_to_mem_thumb32(0x07ff2fff);
else
mask = __opcode_to_mem_arm(0x00ffffff);
/*
* 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:
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
/*
* We only have to consider branch targets that resolve
* to undefined symbols. This is not simply a heuristic,
* it is a fundamental limitation, since the PLT itself
* is part of the module, and needs to be within range
* as well, so modules can never grow beyond that limit.
*/
s = syms + ELF32_R_SYM(rel[i].r_info);
if (s->st_shndx != SHN_UNDEF)
break;
if (!duplicate_rel(base, rel, i, mask))
ret++;
}
}
return ret;
}
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
unsigned long plts = 0;
Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
Elf32_Sym *syms = NULL;
/*
* To store the PLTs, we expand the .text section for core module code
* and for initialization code.
*/
for (s = sechdrs; s < sechdrs_end; ++s) {
if (strcmp(".plt", secstrings + s->sh_name) == 0)
mod->arch.plt = s;
else if (s->sh_type == SHT_SYMTAB)
syms = (Elf32_Sym *)s->sh_addr;
}
if (!mod->arch.plt) {
pr_err("%s: module PLT section missing\n", mod->name);
return -ENOEXEC;
}
if (!syms) {
pr_err("%s: module symtab section 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;
/* ignore relocations that operate on non-exec sections */
if (!(dstsec->sh_flags & SHF_EXECINSTR))
continue;
plts += count_plts(syms, dstsec->sh_addr, rels, numrels);
}
mod->arch.plt->sh_type = SHT_NOBITS;
mod->arch.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
mod->arch.plt->sh_addralign = L1_CACHE_BYTES;
mod->arch.plt->sh_size = round_up(plts * PLT_ENT_SIZE,
sizeof(struct plt_entries));
mod->arch.plt_count = 0;
pr_debug("%s: plt=%x\n", __func__, mod->arch.plt->sh_size);
return 0;
}
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