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linux-stable/arch/s390/kernel/module.c
Ilya Leoshkevich de5012b41e s390/ftrace: implement hotpatching 
s390 allows hotpatching the mask of a conditional jump instruction.
Make use of this feature in order to avoid the expensive stop_machine()
call.

The new trampolines are split in 3 stages:

- A first stage is a 6-byte relative conditional long branch located at
  each function's entry point. Its offset always points to the second
  stage for the corresponding function, and its mask is either all 0s
  (ftrace off) or all 1s (ftrace on). The code for flipping the mask is
  borrowed from ftrace_{enable,disable}_ftrace_graph_caller. After
  flipping, ftrace_arch_code_modify_post_process() syncs with all the
  other CPUs by sending SIGPs.

- Second stages for vmlinux are stored in a separate part of the .text
  section reserved by the linker script, and in dynamically allocated
  memory for modules. This prevents the icache pollution. The total
  size of second stages is about 1.5% of that of the kernel image.

  Putting second stages in the .bss section is possible and decreases
  the size of the non-compressed vmlinux, but splits the kernel 1:1
  mapping, which is a bad tradeoff.

  Each second stage contains a call to the third stage, a pointer to
  the part of the intercepted function right after the first stage, and
  a pointer to an interceptor function (e.g. ftrace_caller).

  Second stages are 8-byte aligned for the future direct calls
  implementation.

- There are only two copies of the third stage: in the .text section
  for vmlinux and in dynamically allocated memory for modules. It can be
  an expoline, which is relatively large, so inlining it into each
  second stage is prohibitively expensive.

As a result of this organization, phoronix-test-suite with ftrace off
does not show any performance degradation.

Suggested-by: Sven Schnelle <svens@linux.ibm.com>
Suggested-by: Vasily Gorbik <gor@linux.ibm.com>
Co-developed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20210728212546.128248-3-iii@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
2021-08-03 14:31:40 +02:00

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// SPDX-License-Identifier: GPL-2.0+
/*
* Kernel module help for s390.
*
* S390 version
* Copyright IBM Corp. 2002, 2003
* Author(s): Arnd Bergmann (arndb@de.ibm.com)
* Martin Schwidefsky (schwidefsky@de.ibm.com)
*
* based on i386 version
* Copyright (C) 2001 Rusty Russell.
*/
#include <linux/module.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/ftrace.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/kasan.h>
#include <linux/moduleloader.h>
#include <linux/bug.h>
#include <linux/memory.h>
#include <asm/alternative.h>
#include <asm/nospec-branch.h>
#include <asm/facility.h>
#include <asm/ftrace.lds.h>
#include <asm/set_memory.h>
#if 0
#define DEBUGP printk
#else
#define DEBUGP(fmt , ...)
#endif
#define PLT_ENTRY_SIZE 20
void *module_alloc(unsigned long size)
{
void *p;
if (PAGE_ALIGN(size) > MODULES_LEN)
return NULL;
p = __vmalloc_node_range(size, MODULE_ALIGN, MODULES_VADDR, MODULES_END,
GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
__builtin_return_address(0));
if (p && (kasan_module_alloc(p, size) < 0)) {
vfree(p);
return NULL;
}
return p;
}
#ifdef CONFIG_FUNCTION_TRACER
void module_arch_cleanup(struct module *mod)
{
module_memfree(mod->arch.trampolines_start);
}
#endif
void module_arch_freeing_init(struct module *mod)
{
if (is_livepatch_module(mod) &&
mod->state == MODULE_STATE_LIVE)
return;
vfree(mod->arch.syminfo);
mod->arch.syminfo = NULL;
}
static void check_rela(Elf_Rela *rela, struct module *me)
{
struct mod_arch_syminfo *info;
info = me->arch.syminfo + ELF_R_SYM (rela->r_info);
switch (ELF_R_TYPE (rela->r_info)) {
case R_390_GOT12: /* 12 bit GOT offset. */
case R_390_GOT16: /* 16 bit GOT offset. */
case R_390_GOT20: /* 20 bit GOT offset. */
case R_390_GOT32: /* 32 bit GOT offset. */
case R_390_GOT64: /* 64 bit GOT offset. */
case R_390_GOTENT: /* 32 bit PC rel. to GOT entry shifted by 1. */
case R_390_GOTPLT12: /* 12 bit offset to jump slot. */
case R_390_GOTPLT16: /* 16 bit offset to jump slot. */
case R_390_GOTPLT20: /* 20 bit offset to jump slot. */
case R_390_GOTPLT32: /* 32 bit offset to jump slot. */
case R_390_GOTPLT64: /* 64 bit offset to jump slot. */
case R_390_GOTPLTENT: /* 32 bit rel. offset to jump slot >> 1. */
if (info->got_offset == -1UL) {
info->got_offset = me->arch.got_size;
me->arch.got_size += sizeof(void*);
}
break;
case R_390_PLT16DBL: /* 16 bit PC rel. PLT shifted by 1. */
case R_390_PLT32DBL: /* 32 bit PC rel. PLT shifted by 1. */
case R_390_PLT32: /* 32 bit PC relative PLT address. */
case R_390_PLT64: /* 64 bit PC relative PLT address. */
case R_390_PLTOFF16: /* 16 bit offset from GOT to PLT. */
case R_390_PLTOFF32: /* 32 bit offset from GOT to PLT. */
case R_390_PLTOFF64: /* 16 bit offset from GOT to PLT. */
if (info->plt_offset == -1UL) {
info->plt_offset = me->arch.plt_size;
me->arch.plt_size += PLT_ENTRY_SIZE;
}
break;
case R_390_COPY:
case R_390_GLOB_DAT:
case R_390_JMP_SLOT:
case R_390_RELATIVE:
/* Only needed if we want to support loading of
modules linked with -shared. */
break;
}
}
/*
* Account for GOT and PLT relocations. We can't add sections for
* got and plt but we can increase the core module size.
*/
int module_frob_arch_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *me)
{
Elf_Shdr *symtab;
Elf_Sym *symbols;
Elf_Rela *rela;
char *strings;
int nrela, i, j;
/* Find symbol table and string table. */
symtab = NULL;
for (i = 0; i < hdr->e_shnum; i++)
switch (sechdrs[i].sh_type) {
case SHT_SYMTAB:
symtab = sechdrs + i;
break;
}
if (!symtab) {
printk(KERN_ERR "module %s: no symbol table\n", me->name);
return -ENOEXEC;
}
/* Allocate one syminfo structure per symbol. */
me->arch.nsyms = symtab->sh_size / sizeof(Elf_Sym);
me->arch.syminfo = vmalloc(array_size(sizeof(struct mod_arch_syminfo),
me->arch.nsyms));
if (!me->arch.syminfo)
return -ENOMEM;
symbols = (void *) hdr + symtab->sh_offset;
strings = (void *) hdr + sechdrs[symtab->sh_link].sh_offset;
for (i = 0; i < me->arch.nsyms; i++) {
if (symbols[i].st_shndx == SHN_UNDEF &&
strcmp(strings + symbols[i].st_name,
"_GLOBAL_OFFSET_TABLE_") == 0)
/* "Define" it as absolute. */
symbols[i].st_shndx = SHN_ABS;
me->arch.syminfo[i].got_offset = -1UL;
me->arch.syminfo[i].plt_offset = -1UL;
me->arch.syminfo[i].got_initialized = 0;
me->arch.syminfo[i].plt_initialized = 0;
}
/* Search for got/plt relocations. */
me->arch.got_size = me->arch.plt_size = 0;
for (i = 0; i < hdr->e_shnum; i++) {
if (sechdrs[i].sh_type != SHT_RELA)
continue;
nrela = sechdrs[i].sh_size / sizeof(Elf_Rela);
rela = (void *) hdr + sechdrs[i].sh_offset;
for (j = 0; j < nrela; j++)
check_rela(rela + j, me);
}
/* Increase core size by size of got & plt and set start
offsets for got and plt. */
me->core_layout.size = ALIGN(me->core_layout.size, 4);
me->arch.got_offset = me->core_layout.size;
me->core_layout.size += me->arch.got_size;
me->arch.plt_offset = me->core_layout.size;
if (me->arch.plt_size) {
if (IS_ENABLED(CONFIG_EXPOLINE) && !nospec_disable)
me->arch.plt_size += PLT_ENTRY_SIZE;
me->core_layout.size += me->arch.plt_size;
}
return 0;
}
static int apply_rela_bits(Elf_Addr loc, Elf_Addr val,
int sign, int bits, int shift,
void *(*write)(void *dest, const void *src, size_t len))
{
unsigned long umax;
long min, max;
void *dest = (void *)loc;
if (val & ((1UL << shift) - 1))
return -ENOEXEC;
if (sign) {
val = (Elf_Addr)(((long) val) >> shift);
min = -(1L << (bits - 1));
max = (1L << (bits - 1)) - 1;
if ((long) val < min || (long) val > max)
return -ENOEXEC;
} else {
val >>= shift;
umax = ((1UL << (bits - 1)) << 1) - 1;
if ((unsigned long) val > umax)
return -ENOEXEC;
}
if (bits == 8) {
unsigned char tmp = val;
write(dest, &tmp, 1);
} else if (bits == 12) {
unsigned short tmp = (val & 0xfff) |
(*(unsigned short *) loc & 0xf000);
write(dest, &tmp, 2);
} else if (bits == 16) {
unsigned short tmp = val;
write(dest, &tmp, 2);
} else if (bits == 20) {
unsigned int tmp = (val & 0xfff) << 16 |
(val & 0xff000) >> 4 | (*(unsigned int *) loc & 0xf00000ff);
write(dest, &tmp, 4);
} else if (bits == 32) {
unsigned int tmp = val;
write(dest, &tmp, 4);
} else if (bits == 64) {
unsigned long tmp = val;
write(dest, &tmp, 8);
}
return 0;
}
static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab,
const char *strtab, struct module *me,
void *(*write)(void *dest, const void *src, size_t len))
{
struct mod_arch_syminfo *info;
Elf_Addr loc, val;
int r_type, r_sym;
int rc = -ENOEXEC;
/* This is where to make the change */
loc = base + rela->r_offset;
/* This is the symbol it is referring to. Note that all
undefined symbols have been resolved. */
r_sym = ELF_R_SYM(rela->r_info);
r_type = ELF_R_TYPE(rela->r_info);
info = me->arch.syminfo + r_sym;
val = symtab[r_sym].st_value;
switch (r_type) {
case R_390_NONE: /* No relocation. */
rc = 0;
break;
case R_390_8: /* Direct 8 bit. */
case R_390_12: /* Direct 12 bit. */
case R_390_16: /* Direct 16 bit. */
case R_390_20: /* Direct 20 bit. */
case R_390_32: /* Direct 32 bit. */
case R_390_64: /* Direct 64 bit. */
val += rela->r_addend;
if (r_type == R_390_8)
rc = apply_rela_bits(loc, val, 0, 8, 0, write);
else if (r_type == R_390_12)
rc = apply_rela_bits(loc, val, 0, 12, 0, write);
else if (r_type == R_390_16)
rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_20)
rc = apply_rela_bits(loc, val, 1, 20, 0, write);
else if (r_type == R_390_32)
rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_64)
rc = apply_rela_bits(loc, val, 0, 64, 0, write);
break;
case R_390_PC16: /* PC relative 16 bit. */
case R_390_PC16DBL: /* PC relative 16 bit shifted by 1. */
case R_390_PC32DBL: /* PC relative 32 bit shifted by 1. */
case R_390_PC32: /* PC relative 32 bit. */
case R_390_PC64: /* PC relative 64 bit. */
val += rela->r_addend - loc;
if (r_type == R_390_PC16)
rc = apply_rela_bits(loc, val, 1, 16, 0, write);
else if (r_type == R_390_PC16DBL)
rc = apply_rela_bits(loc, val, 1, 16, 1, write);
else if (r_type == R_390_PC32DBL)
rc = apply_rela_bits(loc, val, 1, 32, 1, write);
else if (r_type == R_390_PC32)
rc = apply_rela_bits(loc, val, 1, 32, 0, write);
else if (r_type == R_390_PC64)
rc = apply_rela_bits(loc, val, 1, 64, 0, write);
break;
case R_390_GOT12: /* 12 bit GOT offset. */
case R_390_GOT16: /* 16 bit GOT offset. */
case R_390_GOT20: /* 20 bit GOT offset. */
case R_390_GOT32: /* 32 bit GOT offset. */
case R_390_GOT64: /* 64 bit GOT offset. */
case R_390_GOTENT: /* 32 bit PC rel. to GOT entry shifted by 1. */
case R_390_GOTPLT12: /* 12 bit offset to jump slot. */
case R_390_GOTPLT20: /* 20 bit offset to jump slot. */
case R_390_GOTPLT16: /* 16 bit offset to jump slot. */
case R_390_GOTPLT32: /* 32 bit offset to jump slot. */
case R_390_GOTPLT64: /* 64 bit offset to jump slot. */
case R_390_GOTPLTENT: /* 32 bit rel. offset to jump slot >> 1. */
if (info->got_initialized == 0) {
Elf_Addr *gotent = me->core_layout.base +
me->arch.got_offset +
info->got_offset;
write(gotent, &val, sizeof(*gotent));
info->got_initialized = 1;
}
val = info->got_offset + rela->r_addend;
if (r_type == R_390_GOT12 ||
r_type == R_390_GOTPLT12)
rc = apply_rela_bits(loc, val, 0, 12, 0, write);
else if (r_type == R_390_GOT16 ||
r_type == R_390_GOTPLT16)
rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_GOT20 ||
r_type == R_390_GOTPLT20)
rc = apply_rela_bits(loc, val, 1, 20, 0, write);
else if (r_type == R_390_GOT32 ||
r_type == R_390_GOTPLT32)
rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_GOT64 ||
r_type == R_390_GOTPLT64)
rc = apply_rela_bits(loc, val, 0, 64, 0, write);
else if (r_type == R_390_GOTENT ||
r_type == R_390_GOTPLTENT) {
val += (Elf_Addr) me->core_layout.base - loc;
rc = apply_rela_bits(loc, val, 1, 32, 1, write);
}
break;
case R_390_PLT16DBL: /* 16 bit PC rel. PLT shifted by 1. */
case R_390_PLT32DBL: /* 32 bit PC rel. PLT shifted by 1. */
case R_390_PLT32: /* 32 bit PC relative PLT address. */
case R_390_PLT64: /* 64 bit PC relative PLT address. */
case R_390_PLTOFF16: /* 16 bit offset from GOT to PLT. */
case R_390_PLTOFF32: /* 32 bit offset from GOT to PLT. */
case R_390_PLTOFF64: /* 16 bit offset from GOT to PLT. */
if (info->plt_initialized == 0) {
unsigned int insn[5];
unsigned int *ip = me->core_layout.base +
me->arch.plt_offset +
info->plt_offset;
insn[0] = 0x0d10e310; /* basr 1,0 */
insn[1] = 0x100a0004; /* lg 1,10(1) */
if (IS_ENABLED(CONFIG_EXPOLINE) && !nospec_disable) {
unsigned int *ij;
ij = me->core_layout.base +
me->arch.plt_offset +
me->arch.plt_size - PLT_ENTRY_SIZE;
insn[2] = 0xa7f40000 + /* j __jump_r1 */
(unsigned int)(u16)
(((unsigned long) ij - 8 -
(unsigned long) ip) / 2);
} else {
insn[2] = 0x07f10000; /* br %r1 */
}
insn[3] = (unsigned int) (val >> 32);
insn[4] = (unsigned int) val;
write(ip, insn, sizeof(insn));
info->plt_initialized = 1;
}
if (r_type == R_390_PLTOFF16 ||
r_type == R_390_PLTOFF32 ||
r_type == R_390_PLTOFF64)
val = me->arch.plt_offset - me->arch.got_offset +
info->plt_offset + rela->r_addend;
else {
if (!((r_type == R_390_PLT16DBL &&
val - loc + 0xffffUL < 0x1ffffeUL) ||
(r_type == R_390_PLT32DBL &&
val - loc + 0xffffffffULL < 0x1fffffffeULL)))
val = (Elf_Addr) me->core_layout.base +
me->arch.plt_offset +
info->plt_offset;
val += rela->r_addend - loc;
}
if (r_type == R_390_PLT16DBL)
rc = apply_rela_bits(loc, val, 1, 16, 1, write);
else if (r_type == R_390_PLTOFF16)
rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_PLT32DBL)
rc = apply_rela_bits(loc, val, 1, 32, 1, write);
else if (r_type == R_390_PLT32 ||
r_type == R_390_PLTOFF32)
rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_PLT64 ||
r_type == R_390_PLTOFF64)
rc = apply_rela_bits(loc, val, 0, 64, 0, write);
break;
case R_390_GOTOFF16: /* 16 bit offset to GOT. */
case R_390_GOTOFF32: /* 32 bit offset to GOT. */
case R_390_GOTOFF64: /* 64 bit offset to GOT. */
val = val + rela->r_addend -
((Elf_Addr) me->core_layout.base + me->arch.got_offset);
if (r_type == R_390_GOTOFF16)
rc = apply_rela_bits(loc, val, 0, 16, 0, write);
else if (r_type == R_390_GOTOFF32)
rc = apply_rela_bits(loc, val, 0, 32, 0, write);
else if (r_type == R_390_GOTOFF64)
rc = apply_rela_bits(loc, val, 0, 64, 0, write);
break;
case R_390_GOTPC: /* 32 bit PC relative offset to GOT. */
case R_390_GOTPCDBL: /* 32 bit PC rel. off. to GOT shifted by 1. */
val = (Elf_Addr) me->core_layout.base + me->arch.got_offset +
rela->r_addend - loc;
if (r_type == R_390_GOTPC)
rc = apply_rela_bits(loc, val, 1, 32, 0, write);
else if (r_type == R_390_GOTPCDBL)
rc = apply_rela_bits(loc, val, 1, 32, 1, write);
break;
case R_390_COPY:
case R_390_GLOB_DAT: /* Create GOT entry. */
case R_390_JMP_SLOT: /* Create PLT entry. */
case R_390_RELATIVE: /* Adjust by program base. */
/* Only needed if we want to support loading of
modules linked with -shared. */
return -ENOEXEC;
default:
printk(KERN_ERR "module %s: unknown relocation: %u\n",
me->name, r_type);
return -ENOEXEC;
}
if (rc) {
printk(KERN_ERR "module %s: relocation error for symbol %s "
"(r_type %i, value 0x%lx)\n",
me->name, strtab + symtab[r_sym].st_name,
r_type, (unsigned long) val);
return rc;
}
return 0;
}
static int __apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
unsigned int symindex, unsigned int relsec,
struct module *me,
void *(*write)(void *dest, const void *src, size_t len))
{
Elf_Addr base;
Elf_Sym *symtab;
Elf_Rela *rela;
unsigned long i, n;
int rc;
DEBUGP("Applying relocate section %u to %u\n",
relsec, sechdrs[relsec].sh_info);
base = sechdrs[sechdrs[relsec].sh_info].sh_addr;
symtab = (Elf_Sym *) sechdrs[symindex].sh_addr;
rela = (Elf_Rela *) sechdrs[relsec].sh_addr;
n = sechdrs[relsec].sh_size / sizeof(Elf_Rela);
for (i = 0; i < n; i++, rela++) {
rc = apply_rela(rela, base, symtab, strtab, me, write);
if (rc)
return rc;
}
return 0;
}
int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
unsigned int symindex, unsigned int relsec,
struct module *me)
{
bool early = me->state == MODULE_STATE_UNFORMED;
void *(*write)(void *, const void *, size_t) = memcpy;
if (!early)
write = s390_kernel_write;
return __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
write);
}
#ifdef CONFIG_FUNCTION_TRACER
static int module_alloc_ftrace_hotpatch_trampolines(struct module *me,
const Elf_Shdr *s)
{
char *start, *end;
int numpages;
size_t size;
size = FTRACE_HOTPATCH_TRAMPOLINES_SIZE(s->sh_size);
numpages = DIV_ROUND_UP(size, PAGE_SIZE);
start = module_alloc(numpages * PAGE_SIZE);
if (!start)
return -ENOMEM;
set_memory_ro((unsigned long)start, numpages);
end = start + size;
me->arch.trampolines_start = (struct ftrace_hotpatch_trampoline *)start;
me->arch.trampolines_end = (struct ftrace_hotpatch_trampoline *)end;
me->arch.next_trampoline = me->arch.trampolines_start;
return 0;
}
#endif /* CONFIG_FUNCTION_TRACER */
int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *me)
{
const Elf_Shdr *s;
char *secstrings, *secname;
void *aseg;
#ifdef CONFIG_FUNCTION_TRACER
int ret;
#endif
if (IS_ENABLED(CONFIG_EXPOLINE) &&
!nospec_disable && me->arch.plt_size) {
unsigned int *ij;
ij = me->core_layout.base + me->arch.plt_offset +
me->arch.plt_size - PLT_ENTRY_SIZE;
if (test_facility(35)) {
ij[0] = 0xc6000000; /* exrl %r0,.+10 */
ij[1] = 0x0005a7f4; /* j . */
ij[2] = 0x000007f1; /* br %r1 */
} else {
ij[0] = 0x44000000 | (unsigned int)
offsetof(struct lowcore, br_r1_trampoline);
ij[1] = 0xa7f40000; /* j . */
}
}
secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
aseg = (void *) s->sh_addr;
secname = secstrings + s->sh_name;
if (!strcmp(".altinstructions", secname))
/* patch .altinstructions */
apply_alternatives(aseg, aseg + s->sh_size);
if (IS_ENABLED(CONFIG_EXPOLINE) &&
(str_has_prefix(secname, ".s390_indirect")))
nospec_revert(aseg, aseg + s->sh_size);
if (IS_ENABLED(CONFIG_EXPOLINE) &&
(str_has_prefix(secname, ".s390_return")))
nospec_revert(aseg, aseg + s->sh_size);
#ifdef CONFIG_FUNCTION_TRACER
if (!strcmp(FTRACE_CALLSITE_SECTION, secname)) {
ret = module_alloc_ftrace_hotpatch_trampolines(me, s);
if (ret < 0)
return ret;
}
#endif /* CONFIG_FUNCTION_TRACER */
}
jump_label_apply_nops(me);
return 0;
}
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