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linux-sg2042/arch/arm/kernel/module-plts.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
*/
#include <linux/elf.h>
#include <linux/ftrace.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
#include <linux/moduleloader.h>
#include <asm/cache.h>
#include <asm/opcodes.h>
#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
static const u32 fixed_plts[] = {
#ifdef CONFIG_DYNAMIC_FTRACE
FTRACE_ADDR,
MCOUNT_ADDR,
#endif
};
static bool in_init(const struct module *mod, unsigned long loc)
{
return loc - (u32)mod->init_layout.base < mod->init_layout.size;
}
static void prealloc_fixed(struct mod_plt_sec *pltsec, struct plt_entries *plt)
{
int i;
if (!ARRAY_SIZE(fixed_plts) || pltsec->plt_count)
return;
pltsec->plt_count = ARRAY_SIZE(fixed_plts);
for (i = 0; i < ARRAY_SIZE(plt->ldr); ++i)
plt->ldr[i] = PLT_ENT_LDR;
BUILD_BUG_ON(sizeof(fixed_plts) > sizeof(plt->lit));
memcpy(plt->lit, fixed_plts, sizeof(fixed_plts));
}
u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
&mod->arch.init;
struct plt_entries *plt;
int idx;
/* cache the address, ELF header is available only during module load */
if (!pltsec->plt_ent)
pltsec->plt_ent = (struct plt_entries *)pltsec->plt->sh_addr;
plt = pltsec->plt_ent;
prealloc_fixed(pltsec, plt);
for (idx = 0; idx < ARRAY_SIZE(fixed_plts); ++idx)
if (plt->lit[idx] == val)
return (u32)&plt->ldr[idx];
idx = 0;
/*
* Look for an existing entry pointing to 'val'. Given that the
* relocations are sorted, this will be the last entry we allocated.
* (if one exists).
*/
if (pltsec->plt_count > 0) {
plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
if (plt->lit[idx] == val)
return (u32)&plt->ldr[idx];
idx = (idx + 1) % PLT_ENT_COUNT;
if (!idx)
plt++;
}
pltsec->plt_count++;
BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size);
if (!idx)
/* Populate a new set of entries */
*plt = (struct plt_entries){
{ [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
{ val, }
};
else
plt->lit[idx] = val;
return (u32)&plt->ldr[idx];
}
#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
static int cmp_rel(const void *a, const void *b)
{
const Elf32_Rel *x = a, *y = b;
int i;
/* sort by type and symbol index */
i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info));
if (i == 0)
i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info));
return i;
}
static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel)
{
u32 *tval = (u32 *)(base + rel->r_offset);
/*
* Do a bitwise compare on the raw addend rather than fully decoding
* the offset and doing an arithmetic comparison.
* Note that a zero-addend jump/call relocation is encoded taking the
* PC bias into account, i.e., -8 for ARM and -4 for Thumb2.
*/
switch (ELF32_R_TYPE(rel->r_info)) {
u16 upper, lower;
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]);
lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]);
return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe;
case R_ARM_CALL:
case R_ARM_PC24:
case R_ARM_JUMP24:
return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe;
}
BUG();
}
static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num)
{
const Elf32_Rel *prev;
/*
* Entries are sorted by type and symbol index. That means that,
* if a duplicate entry exists, it must be in the preceding
* slot.
*/
if (!num)
return false;
prev = rel + num - 1;
return cmp_rel(rel + num, prev) == 0 &&
is_zero_addend_relocation(base, prev);
}
/* 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, Elf32_Word dstidx)
{
unsigned int ret = 0;
const Elf32_Sym *s;
int i;
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 symbols that are defined in a different section.
* This is not simply a heuristic, it is a fundamental
* limitation, since there is no guaranteed way to emit
* PLT entries sufficiently close to the branch if the
* section size exceeds the range of a branch
* instruction. So ignore relocations against defined
* symbols if they live in the same section as the
* relocation target.
*/
s = syms + ELF32_R_SYM(rel[i].r_info);
if (s->st_shndx == dstidx)
break;
/*
* Jump relocations with non-zero addends against
* undefined symbols are supported by the ELF spec, but
* do not occur in practice (e.g., 'jump n bytes past
* the entry point of undefined function symbol f').
* So we need to support them, but there is no need to
* take them into consideration when trying to optimize
* this code. So let's only check for duplicates when
* the addend is zero. (Note that calls into the core
* module via init PLT entries could involve section
* relative symbol references with non-zero addends, for
* which we may end up emitting duplicates, but the init
* PLT is released along with the rest of the .init
* region as soon as module loading completes.)
*/
if (!is_zero_addend_relocation(base, rel + i) ||
!duplicate_rel(base, rel, i))
ret++;
}
}
return ret;
}
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
unsigned long core_plts = ARRAY_SIZE(fixed_plts);
unsigned long init_plts = ARRAY_SIZE(fixed_plts);
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.core.plt = s;
else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
mod->arch.init.plt = s;
else if (s->sh_type == SHT_SYMTAB)
syms = (Elf32_Sym *)s->sh_addr;
}
if (!mod->arch.core.plt || !mod->arch.init.plt) {
pr_err("%s: module PLT section(s) 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) {
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;
/* sort by type and symbol index */
sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL);
if (strncmp(secstrings + dstsec->sh_name, ".init", 5) != 0)
core_plts += count_plts(syms, dstsec->sh_addr, rels,
numrels, s->sh_info);
else
init_plts += count_plts(syms, dstsec->sh_addr, rels,
numrels, s->sh_info);
}
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.core.plt_ent = NULL;
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;
mod->arch.init.plt_ent = NULL;
pr_debug("%s: plt=%x, init.plt=%x\n", __func__,
mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
return 0;
}
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