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linux/arch/arm/kernel/module.c
Ard Biesheuvel 7d485f647c ARM: 8220/1: allow modules outside of bl range 
Loading modules far away from the kernel in memory is problematic
because the 'bl' instruction only has limited reach, and modules are not
built with PLTs. Instead of using the -mlong-calls option (which affects
all compiler emitted bl instructions, but not the ones in assembler),
this patch allocates some additional space at module load time, and
populates it with PLT like veneers when encountering relocations that
are out of range.

This should work with all relocations against symbols exported by the
kernel, including those resulting from GCC generated implicit function
calls for ftrace etc.

The module memory size increases by about 5% on average, regardless of
whether any PLT entries were actually needed. However, due to the page
based rounding that occurs when allocating module memory, the average
memory footprint increase is negligible.

Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2015-05-08 10:42:34 +01:00

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/*
* linux/arch/arm/kernel/module.c
*
* Copyright (C) 2002 Russell King.
* Modified for nommu by Hyok S. Choi
*
* 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.
*
* Module allocation method suggested by Andi Kleen.
*/
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/gfp.h>
#include <asm/pgtable.h>
#include <asm/sections.h>
#include <asm/smp_plat.h>
#include <asm/unwind.h>
#include <asm/opcodes.h>
#ifdef CONFIG_XIP_KERNEL
/*
* The XIP kernel text is mapped in the module area for modules and
* some other stuff to work without any indirect relocations.
* MODULES_VADDR is redefined here and not in asm/memory.h to avoid
* recompiling the whole kernel when CONFIG_XIP_KERNEL is turned on/off.
*/
#undef MODULES_VADDR
#define MODULES_VADDR (((unsigned long)_etext + ~PMD_MASK) & PMD_MASK)
#endif
#ifdef CONFIG_MMU
void *module_alloc(unsigned long size)
{
void *p = __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
__builtin_return_address(0));
if (!IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || p)
return p;
return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
__builtin_return_address(0));
}
#endif
int
apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex,
unsigned int relindex, struct module *module)
{
Elf32_Shdr *symsec = sechdrs + symindex;
Elf32_Shdr *relsec = sechdrs + relindex;
Elf32_Shdr *dstsec = sechdrs + relsec->sh_info;
Elf32_Rel *rel = (void *)relsec->sh_addr;
unsigned int i;
for (i = 0; i < relsec->sh_size / sizeof(Elf32_Rel); i++, rel++) {
unsigned long loc;
Elf32_Sym *sym;
const char *symname;
s32 offset;
u32 tmp;
#ifdef CONFIG_THUMB2_KERNEL
u32 upper, lower, sign, j1, j2;
#endif
offset = ELF32_R_SYM(rel->r_info);
if (offset < 0 || offset > (symsec->sh_size / sizeof(Elf32_Sym))) {
pr_err("%s: section %u reloc %u: bad relocation sym offset\n",
module->name, relindex, i);
return -ENOEXEC;
}
sym = ((Elf32_Sym *)symsec->sh_addr) + offset;
symname = strtab + sym->st_name;
if (rel->r_offset < 0 || rel->r_offset > dstsec->sh_size - sizeof(u32)) {
pr_err("%s: section %u reloc %u sym '%s': out of bounds relocation, offset %d size %u\n",
module->name, relindex, i, symname,
rel->r_offset, dstsec->sh_size);
return -ENOEXEC;
}
loc = dstsec->sh_addr + rel->r_offset;
switch (ELF32_R_TYPE(rel->r_info)) {
case R_ARM_NONE:
/* ignore */
break;
case R_ARM_ABS32:
case R_ARM_TARGET1:
*(u32 *)loc += sym->st_value;
break;
case R_ARM_PC24:
case R_ARM_CALL:
case R_ARM_JUMP24:
if (sym->st_value & 3) {
pr_err("%s: section %u reloc %u sym '%s': unsupported interworking call (ARM -> Thumb)\n",
module->name, relindex, i, symname);
return -ENOEXEC;
}
offset = __mem_to_opcode_arm(*(u32 *)loc);
offset = (offset & 0x00ffffff) << 2;
if (offset & 0x02000000)
offset -= 0x04000000;
offset += sym->st_value - loc;
/*
* Route through a PLT entry if 'offset' exceeds the
* supported range. Note that 'offset + loc + 8'
* contains the absolute jump target, i.e.,
* @sym + addend, corrected for the +8 PC bias.
*/
if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
(offset <= (s32)0xfe000000 ||
offset >= (s32)0x02000000))
offset = get_module_plt(module, loc,
offset + loc + 8)
- loc - 8;
if (offset <= (s32)0xfe000000 ||
offset >= (s32)0x02000000) {
pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
module->name, relindex, i, symname,
ELF32_R_TYPE(rel->r_info), loc,
sym->st_value);
return -ENOEXEC;
}
offset >>= 2;
offset &= 0x00ffffff;
*(u32 *)loc &= __opcode_to_mem_arm(0xff000000);
*(u32 *)loc |= __opcode_to_mem_arm(offset);
break;
case R_ARM_V4BX:
/* Preserve Rm and the condition code. Alter
* other bits to re-code instruction as
* MOV PC,Rm.
*/
*(u32 *)loc &= __opcode_to_mem_arm(0xf000000f);
*(u32 *)loc |= __opcode_to_mem_arm(0x01a0f000);
break;
case R_ARM_PREL31:
offset = *(u32 *)loc + sym->st_value - loc;
*(u32 *)loc = offset & 0x7fffffff;
break;
case R_ARM_MOVW_ABS_NC:
case R_ARM_MOVT_ABS:
offset = tmp = __mem_to_opcode_arm(*(u32 *)loc);
offset = ((offset & 0xf0000) >> 4) | (offset & 0xfff);
offset = (offset ^ 0x8000) - 0x8000;
offset += sym->st_value;
if (ELF32_R_TYPE(rel->r_info) == R_ARM_MOVT_ABS)
offset >>= 16;
tmp &= 0xfff0f000;
tmp |= ((offset & 0xf000) << 4) |
(offset & 0x0fff);
*(u32 *)loc = __opcode_to_mem_arm(tmp);
break;
#ifdef CONFIG_THUMB2_KERNEL
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
/*
* For function symbols, only Thumb addresses are
* allowed (no interworking).
*
* For non-function symbols, the destination
* has no specific ARM/Thumb disposition, so
* the branch is resolved under the assumption
* that interworking is not required.
*/
if (ELF32_ST_TYPE(sym->st_info) == STT_FUNC &&
!(sym->st_value & 1)) {
pr_err("%s: section %u reloc %u sym '%s': unsupported interworking call (Thumb -> ARM)\n",
module->name, relindex, i, symname);
return -ENOEXEC;
}
upper = __mem_to_opcode_thumb16(*(u16 *)loc);
lower = __mem_to_opcode_thumb16(*(u16 *)(loc + 2));
/*
* 25 bit signed address range (Thumb-2 BL and B.W
* instructions):
* S:I1:I2:imm10:imm11:0
* where:
* S = upper[10] = offset[24]
* I1 = ~(J1 ^ S) = offset[23]
* I2 = ~(J2 ^ S) = offset[22]
* imm10 = upper[9:0] = offset[21:12]
* imm11 = lower[10:0] = offset[11:1]
* J1 = lower[13]
* J2 = lower[11]
*/
sign = (upper >> 10) & 1;
j1 = (lower >> 13) & 1;
j2 = (lower >> 11) & 1;
offset = (sign << 24) | ((~(j1 ^ sign) & 1) << 23) |
((~(j2 ^ sign) & 1) << 22) |
((upper & 0x03ff) << 12) |
((lower & 0x07ff) << 1);
if (offset & 0x01000000)
offset -= 0x02000000;
offset += sym->st_value - loc;
/*
* Route through a PLT entry if 'offset' exceeds the
* supported range.
*/
if (IS_ENABLED(CONFIG_ARM_MODULE_PLTS) &&
(offset <= (s32)0xff000000 ||
offset >= (s32)0x01000000))
offset = get_module_plt(module, loc,
offset + loc + 4)
- loc - 4;
if (offset <= (s32)0xff000000 ||
offset >= (s32)0x01000000) {
pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
module->name, relindex, i, symname,
ELF32_R_TYPE(rel->r_info), loc,
sym->st_value);
return -ENOEXEC;
}
sign = (offset >> 24) & 1;
j1 = sign ^ (~(offset >> 23) & 1);
j2 = sign ^ (~(offset >> 22) & 1);
upper = (u16)((upper & 0xf800) | (sign << 10) |
((offset >> 12) & 0x03ff));
lower = (u16)((lower & 0xd000) |
(j1 << 13) | (j2 << 11) |
((offset >> 1) & 0x07ff));
*(u16 *)loc = __opcode_to_mem_thumb16(upper);
*(u16 *)(loc + 2) = __opcode_to_mem_thumb16(lower);
break;
case R_ARM_THM_MOVW_ABS_NC:
case R_ARM_THM_MOVT_ABS:
upper = __mem_to_opcode_thumb16(*(u16 *)loc);
lower = __mem_to_opcode_thumb16(*(u16 *)(loc + 2));
/*
* MOVT/MOVW instructions encoding in Thumb-2:
*
* i = upper[10]
* imm4 = upper[3:0]
* imm3 = lower[14:12]
* imm8 = lower[7:0]
*
* imm16 = imm4:i:imm3:imm8
*/
offset = ((upper & 0x000f) << 12) |
((upper & 0x0400) << 1) |
((lower & 0x7000) >> 4) | (lower & 0x00ff);
offset = (offset ^ 0x8000) - 0x8000;
offset += sym->st_value;
if (ELF32_R_TYPE(rel->r_info) == R_ARM_THM_MOVT_ABS)
offset >>= 16;
upper = (u16)((upper & 0xfbf0) |
((offset & 0xf000) >> 12) |
((offset & 0x0800) >> 1));
lower = (u16)((lower & 0x8f00) |
((offset & 0x0700) << 4) |
(offset & 0x00ff));
*(u16 *)loc = __opcode_to_mem_thumb16(upper);
*(u16 *)(loc + 2) = __opcode_to_mem_thumb16(lower);
break;
#endif
default:
pr_err("%s: unknown relocation: %u\n",
module->name, ELF32_R_TYPE(rel->r_info));
return -ENOEXEC;
}
}
return 0;
}
struct mod_unwind_map {
const Elf_Shdr *unw_sec;
const Elf_Shdr *txt_sec;
};
static const Elf_Shdr *find_mod_section(const Elf32_Ehdr *hdr,
const Elf_Shdr *sechdrs, const char *name)
{
const Elf_Shdr *s, *se;
const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++)
if (strcmp(name, secstrs + s->sh_name) == 0)
return s;
return NULL;
}
extern void fixup_pv_table(const void *, unsigned long);
extern void fixup_smp(const void *, unsigned long);
int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
struct module *mod)
{
const Elf_Shdr *s = NULL;
#ifdef CONFIG_ARM_UNWIND
const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
const Elf_Shdr *sechdrs_end = sechdrs + hdr->e_shnum;
struct mod_unwind_map maps[ARM_SEC_MAX];
int i;
memset(maps, 0, sizeof(maps));
for (s = sechdrs; s < sechdrs_end; s++) {
const char *secname = secstrs + s->sh_name;
if (!(s->sh_flags & SHF_ALLOC))
continue;
if (strcmp(".ARM.exidx.init.text", secname) == 0)
maps[ARM_SEC_INIT].unw_sec = s;
else if (strcmp(".ARM.exidx", secname) == 0)
maps[ARM_SEC_CORE].unw_sec = s;
else if (strcmp(".ARM.exidx.exit.text", secname) == 0)
maps[ARM_SEC_EXIT].unw_sec = s;
else if (strcmp(".ARM.exidx.text.unlikely", secname) == 0)
maps[ARM_SEC_UNLIKELY].unw_sec = s;
else if (strcmp(".ARM.exidx.text.hot", secname) == 0)
maps[ARM_SEC_HOT].unw_sec = s;
else if (strcmp(".init.text", secname) == 0)
maps[ARM_SEC_INIT].txt_sec = s;
else if (strcmp(".text", secname) == 0)
maps[ARM_SEC_CORE].txt_sec = s;
else if (strcmp(".exit.text", secname) == 0)
maps[ARM_SEC_EXIT].txt_sec = s;
else if (strcmp(".text.unlikely", secname) == 0)
maps[ARM_SEC_UNLIKELY].txt_sec = s;
else if (strcmp(".text.hot", secname) == 0)
maps[ARM_SEC_HOT].txt_sec = s;
}
for (i = 0; i < ARM_SEC_MAX; i++)
if (maps[i].unw_sec && maps[i].txt_sec)
mod->arch.unwind[i] =
unwind_table_add(maps[i].unw_sec->sh_addr,
maps[i].unw_sec->sh_size,
maps[i].txt_sec->sh_addr,
maps[i].txt_sec->sh_size);
#endif
#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
s = find_mod_section(hdr, sechdrs, ".pv_table");
if (s)
fixup_pv_table((void *)s->sh_addr, s->sh_size);
#endif
s = find_mod_section(hdr, sechdrs, ".alt.smp.init");
if (s && !is_smp())
#ifdef CONFIG_SMP_ON_UP
fixup_smp((void *)s->sh_addr, s->sh_size);
#else
return -EINVAL;
#endif
return 0;
}
void
module_arch_cleanup(struct module *mod)
{
#ifdef CONFIG_ARM_UNWIND
int i;
for (i = 0; i < ARM_SEC_MAX; i++)
if (mod->arch.unwind[i])
unwind_table_del(mod->arch.unwind[i]);
#endif
}
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