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// SPDX-License-Identifier: GPL-2.0
/*
* jump label x86 support
*
* Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
*
*/
#include <linux/jump_label.h>
#include <linux/memory.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/jhash.h>
#include <linux/cpu.h>
#include <asm/kprobes.h>
#include <asm/alternative.h>
#include <asm/text-patching.h>
union jump_code_union {
char code[JUMP_LABEL_NOP_SIZE];
struct {
char jump;
int offset;
} __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_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, line);
BUG();
}
static void __jump_label_set_jump_code(struct jump_entry *entry,
enum jump_label_type type,
union jump_code_union *code,
int init)
{
const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
const void *expect;
int line;
code->jump = 0xe9;
code->offset = jump_entry_target(entry) -
(jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
if (init) {
expect = default_nop; line = __LINE__;
} else if (type == JUMP_LABEL_JMP) {
expect = ideal_nop; line = __LINE__;
} else {
expect = code->code; line = __LINE__;
}
if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
bug_at((void *)jump_entry_code(entry), line);
if (type == JUMP_LABEL_NOP)
memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE);
}
static void __ref __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
int init)
{
union jump_code_union code;
__jump_label_set_jump_code(entry, type, &code, init);
/*
* As long as only a single processor is running and the code is still
* not marked as RO, text_poke_early() can be used; Checking that
* system_state is SYSTEM_BOOTING guarantees it. It will be set to
* SYSTEM_SCHEDULING before other cores are awaken and before the
* code is write-protected.
*
* At the time the change is being done, just ignore whether we
* are doing nop -> jump or jump -> nop transition, and assume
* always nop being the 'currently valid' instruction
*/
if (init || system_state == SYSTEM_BOOTING) {
text_poke_early((void *)jump_entry_code(entry), &code,
JUMP_LABEL_NOP_SIZE);
return;
}
text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL);
}
void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type)
{
mutex_lock(&text_mutex);
__jump_label_transform(entry, type, 0);
mutex_unlock(&text_mutex);
}
#define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
static struct text_poke_loc tp_vec[TP_VEC_MAX];
static int tp_vec_nr;
bool arch_jump_label_transform_queue(struct jump_entry *entry,
enum jump_label_type type)
{
struct text_poke_loc *tp;
void *entry_code;
if (system_state == SYSTEM_BOOTING) {
/*
* Fallback to the non-batching mode.
*/
arch_jump_label_transform(entry, type);
return true;
}
/*
* No more space in the vector, tell upper layer to apply
* the queue before continuing.
*/
if (tp_vec_nr == TP_VEC_MAX)
return false;
tp = &tp_vec[tp_vec_nr];
entry_code = (void *)jump_entry_code(entry);
/*
* The INT3 handler will do a bsearch in the queue, so we need entries
* to be sorted. We can survive an unsorted list by rejecting the entry,
* forcing the generic jump_label code to apply the queue. Warning once,
* to raise the attention to the case of an unsorted entry that is
* better not happen, because, in the worst case we will perform in the
* same way as we do without batching - with some more overhead.
*/
if (tp_vec_nr > 0) {
int prev = tp_vec_nr - 1;
struct text_poke_loc *prev_tp = &tp_vec[prev];
if (WARN_ON_ONCE(prev_tp->addr > entry_code))
return false;
}
__jump_label_set_jump_code(entry, type,
(union jump_code_union *)&tp->text, 0);
text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL);
tp_vec_nr++;
return true;
}
void arch_jump_label_transform_apply(void)
{
if (!tp_vec_nr)
return;
mutex_lock(&text_mutex);
text_poke_bp_batch(tp_vec, tp_vec_nr);
mutex_unlock(&text_mutex);
tp_vec_nr = 0;
}
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)
{
/*
* 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, 1);
}
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