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Merge branch 'x86/jumplabel' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull x86 jumplabel changes from Peter Anvin:
 "One more x86 tree for this merge window.  This tree improves the
  handling of jump labels, so that most of the time we don't have to do
  a massive initial patching run.

  Furthermore, we will error out of the jump label is not what is
  expected, eg if it has been corrupted or tampered with"

* 'x86/jumplabel' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/jump-label: Show where and what was wrong on errors
  x86/jump-label: Add safety checks to jump label conversions
  x86/jump-label: Do not bother updating nops if they are correct
  x86/jump-label: Use best default nops for inital jump label calls
This commit is contained in:
Linus Torvalds 2013-09-10 19:43:23 -07:00
commit 442e0973e9
2 changed files with 73 additions and 6 deletions
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9
arch/x86/include/asm/jump_label.h
View File

@ -3,18 +3,23 @@
#ifdef __KERNEL__
#include <linux/stringify.h>
#include <linux/types.h>
#include <asm/nops.h>
#include <asm/asm.h>
#define JUMP_LABEL_NOP_SIZE 5
#define STATIC_KEY_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t"
#ifdef CONFIG_X86_64
# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC
#else
# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
#endif
static __always_inline bool arch_static_branch(struct static_key *key)
{
asm goto("1:"
STATIC_KEY_INITIAL_NOP
".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
_ASM_PTR "1b, %l[l_yes], %c0 \n\t"

70
arch/x86/kernel/jump_label.c
View File

@ -24,18 +24,57 @@ union jump_code_union {
} __attribute__((packed));
};
static void bug_at(unsigned char *ip, int line)
{
/*
* The location is not an op that we were expecting.
* Something went wrong. Crash the box, as something could be
* corrupting the kernel.
*/
pr_warning("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n",
ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line);
BUG();
}
static void __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
void *(*poker)(void *, const void *, size_t))
void *(*poker)(void *, const void *, size_t),
int init)
{
union jump_code_union code;
const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
if (type == JUMP_LABEL_ENABLE) {
/*
* We are enabling this jump label. If it is not a nop
* then something must have gone wrong.
*/
if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
bug_at((void *)entry->code, __LINE__);
code.jump = 0xe9;
code.offset = entry->target -
(entry->code + JUMP_LABEL_NOP_SIZE);
} else
} else {
/*
* We are disabling this jump label. If it is not what
* we think it is, then something must have gone wrong.
* If this is the first initialization call, then we
* are converting the default nop to the ideal nop.
*/
if (init) {
const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
bug_at((void *)entry->code, __LINE__);
} else {
code.jump = 0xe9;
code.offset = entry->target -
(entry->code + JUMP_LABEL_NOP_SIZE);
if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
bug_at((void *)entry->code, __LINE__);
}
memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
}
/*
* Make text_poke_bp() a default fallback poker.
@ -57,15 +96,38 @@ void arch_jump_label_transform(struct jump_entry *entry,
{
get_online_cpus();
mutex_lock(&text_mutex);
__jump_label_transform(entry, type, NULL);
__jump_label_transform(entry, type, NULL, 0);
mutex_unlock(&text_mutex);
put_online_cpus();
}
static enum {
JL_STATE_START,
JL_STATE_NO_UPDATE,
JL_STATE_UPDATE,
} jlstate __initdata_or_module = JL_STATE_START;
__init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
enum jump_label_type type)
{
__jump_label_transform(entry, type, text_poke_early);
/*
* This function is called at boot up and when modules are
* first loaded. Check if the default nop, the one that is
* inserted at compile time, is the ideal nop. If it is, then
* we do not need to update the nop, and we can leave it as is.
* If it is not, then we need to update the nop to the ideal nop.
*/
if (jlstate == JL_STATE_START) {
const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
if (memcmp(ideal_nop, default_nop, 5) != 0)
jlstate = JL_STATE_UPDATE;
else
jlstate = JL_STATE_NO_UPDATE;
}
if (jlstate == JL_STATE_UPDATE)
__jump_label_transform(entry, type, text_poke_early, 1);
}
#endif