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linux/arch/x86/kernel/alternative.c

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// SPDX-License-Identifier: GPL-2.0-only
#define pr_fmt(fmt) "SMP alternatives: " fmt
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/stringify.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/memory.h>
#include <linux/stop_machine.h>
#include <linux/slab.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>
#include <linux/mmu_context.h>
#include <linux/bsearch.h>
#include <asm/text-patching.h>
#include <asm/alternative.h>
#include <asm/sections.h>
#include <asm/pgtable.h>
#include <asm/mce.h>
#include <asm/nmi.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
#include <asm/io.h>
#include <asm/fixmap.h>
int __read_mostly alternatives_patched;
EXPORT_SYMBOL_GPL(alternatives_patched);
#define MAX_PATCH_LEN (255-1)
static int __initdata_or_module debug_alternative;
static int __init debug_alt(char *str)
{
debug_alternative = 1;
return 1;
}
__setup("debug-alternative", debug_alt);
static int noreplace_smp;
static int __init setup_noreplace_smp(char *str)
{
noreplace_smp = 1;
return 1;
}
__setup("noreplace-smp", setup_noreplace_smp);
#define DPRINTK(fmt, args...) \
do { \
if (debug_alternative) \
printk(KERN_DEBUG "%s: " fmt "\n", __func__, ##args); \
} while (0)
#define DUMP_BYTES(buf, len, fmt, args...) \
do { \
if (unlikely(debug_alternative)) { \
int j; \
\
if (!(len)) \
break; \
\
printk(KERN_DEBUG fmt, ##args); \
for (j = 0; j < (len) - 1; j++) \
printk(KERN_CONT "%02hhx ", buf[j]); \
printk(KERN_CONT "%02hhx\n", buf[j]); \
} \
} while (0)
/*
* Each GENERIC_NOPX is of X bytes, and defined as an array of bytes
* that correspond to that nop. Getting from one nop to the next, we
* add to the array the offset that is equal to the sum of all sizes of
* nops preceding the one we are after.
*
* Note: The GENERIC_NOP5_ATOMIC is at the end, as it breaks the
* nice symmetry of sizes of the previous nops.
*/
#if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64)
static const unsigned char intelnops[] =
{
GENERIC_NOP1,
GENERIC_NOP2,
GENERIC_NOP3,
GENERIC_NOP4,
GENERIC_NOP5,
GENERIC_NOP6,
GENERIC_NOP7,
GENERIC_NOP8,
GENERIC_NOP5_ATOMIC
};
static const unsigned char * const intel_nops[ASM_NOP_MAX+2] =
{
NULL,
intelnops,
intelnops + 1,
intelnops + 1 + 2,
intelnops + 1 + 2 + 3,
intelnops + 1 + 2 + 3 + 4,
intelnops + 1 + 2 + 3 + 4 + 5,
intelnops + 1 + 2 + 3 + 4 + 5 + 6,
intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
};
#endif
#ifdef K8_NOP1
static const unsigned char k8nops[] =
{
K8_NOP1,
K8_NOP2,
K8_NOP3,
K8_NOP4,
K8_NOP5,
K8_NOP6,
K8_NOP7,
K8_NOP8,
K8_NOP5_ATOMIC
};
static const unsigned char * const k8_nops[ASM_NOP_MAX+2] =
{
NULL,
k8nops,
k8nops + 1,
k8nops + 1 + 2,
k8nops + 1 + 2 + 3,
k8nops + 1 + 2 + 3 + 4,
k8nops + 1 + 2 + 3 + 4 + 5,
k8nops + 1 + 2 + 3 + 4 + 5 + 6,
k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
};
#endif
#if defined(K7_NOP1) && !defined(CONFIG_X86_64)
static const unsigned char k7nops[] =
{
K7_NOP1,
K7_NOP2,
K7_NOP3,
K7_NOP4,
K7_NOP5,
K7_NOP6,
K7_NOP7,
K7_NOP8,
K7_NOP5_ATOMIC
};
static const unsigned char * const k7_nops[ASM_NOP_MAX+2] =
{
NULL,
k7nops,
k7nops + 1,
k7nops + 1 + 2,
k7nops + 1 + 2 + 3,
k7nops + 1 + 2 + 3 + 4,
k7nops + 1 + 2 + 3 + 4 + 5,
k7nops + 1 + 2 + 3 + 4 + 5 + 6,
k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
};
#endif
#ifdef P6_NOP1
static const unsigned char p6nops[] =
{
P6_NOP1,
P6_NOP2,
P6_NOP3,
P6_NOP4,
P6_NOP5,
P6_NOP6,
P6_NOP7,
P6_NOP8,
P6_NOP5_ATOMIC
};
static const unsigned char * const p6_nops[ASM_NOP_MAX+2] =
{
NULL,
p6nops,
p6nops + 1,
p6nops + 1 + 2,
p6nops + 1 + 2 + 3,
p6nops + 1 + 2 + 3 + 4,
p6nops + 1 + 2 + 3 + 4 + 5,
p6nops + 1 + 2 + 3 + 4 + 5 + 6,
p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
};
#endif
/* Initialize these to a safe default */
#ifdef CONFIG_X86_64
const unsigned char * const *ideal_nops = p6_nops;
#else
const unsigned char * const *ideal_nops = intel_nops;
#endif
void __init arch_init_ideal_nops(void)
{
switch (boot_cpu_data.x86_vendor) {
case X86_VENDOR_INTEL:
/*
* Due to a decoder implementation quirk, some
* specific Intel CPUs actually perform better with
* the "k8_nops" than with the SDM-recommended NOPs.
*/
if (boot_cpu_data.x86 == 6 &&
boot_cpu_data.x86_model >= 0x0f &&
boot_cpu_data.x86_model != 0x1c &&
boot_cpu_data.x86_model != 0x26 &&
boot_cpu_data.x86_model != 0x27 &&
boot_cpu_data.x86_model < 0x30) {
ideal_nops = k8_nops;
} else if (boot_cpu_has(X86_FEATURE_NOPL)) {
ideal_nops = p6_nops;
} else {
#ifdef CONFIG_X86_64
ideal_nops = k8_nops;
#else
ideal_nops = intel_nops;
#endif
}
break;
case X86_VENDOR_HYGON:
ideal_nops = p6_nops;
return;
case X86_VENDOR_AMD:
if (boot_cpu_data.x86 > 0xf) {
ideal_nops = p6_nops;
return;
}
/* fall through */
default:
#ifdef CONFIG_X86_64
ideal_nops = k8_nops;
#else
if (boot_cpu_has(X86_FEATURE_K8))
ideal_nops = k8_nops;
else if (boot_cpu_has(X86_FEATURE_K7))
ideal_nops = k7_nops;
else
ideal_nops = intel_nops;
#endif
}
}
/* Use this to add nops to a buffer, then text_poke the whole buffer. */
static void __init_or_module add_nops(void *insns, unsigned int len)
{
while (len > 0) {
unsigned int noplen = len;
if (noplen > ASM_NOP_MAX)
noplen = ASM_NOP_MAX;
memcpy(insns, ideal_nops[noplen], noplen);
insns += noplen;
len -= noplen;
}
}
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern s32 __smp_locks[], __smp_locks_end[];
void text_poke_early(void *addr, const void *opcode, size_t len);
/*
* Are we looking at a near JMP with a 1 or 4-byte displacement.
*/
static inline bool is_jmp(const u8 opcode)
{
return opcode == 0xeb || opcode == 0xe9;
}
static void __init_or_module
recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insn_buff)
{
u8 *next_rip, *tgt_rip;
s32 n_dspl, o_dspl;
int repl_len;
if (a->replacementlen != 5)
return;
o_dspl = *(s32 *)(insn_buff + 1);
/* next_rip of the replacement JMP */
next_rip = repl_insn + a->replacementlen;
/* target rip of the replacement JMP */
tgt_rip = next_rip + o_dspl;
n_dspl = tgt_rip - orig_insn;
DPRINTK("target RIP: %px, new_displ: 0x%x", tgt_rip, n_dspl);
if (tgt_rip - orig_insn >= 0) {
if (n_dspl - 2 <= 127)
goto two_byte_jmp;
else
goto five_byte_jmp;
/* negative offset */
} else {
if (((n_dspl - 2) & 0xff) == (n_dspl - 2))
goto two_byte_jmp;
else
goto five_byte_jmp;
}
two_byte_jmp:
n_dspl -= 2;
insn_buff[0] = 0xeb;
insn_buff[1] = (s8)n_dspl;
add_nops(insn_buff + 2, 3);
repl_len = 2;
goto done;
five_byte_jmp:
n_dspl -= 5;
insn_buff[0] = 0xe9;
*(s32 *)&insn_buff[1] = n_dspl;
repl_len = 5;
done:
DPRINTK("final displ: 0x%08x, JMP 0x%lx",
n_dspl, (unsigned long)orig_insn + n_dspl + repl_len);
}
/*
* "noinline" to cause control flow change and thus invalidate I$ and
* cause refetch after modification.
*/
static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr)
{
unsigned long flags;
int i;
for (i = 0; i < a->padlen; i++) {
if (instr[i] != 0x90)
return;
}
local_irq_save(flags);
add_nops(instr + (a->instrlen - a->padlen), a->padlen);
local_irq_restore(flags);
DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ",
instr, a->instrlen - a->padlen, a->padlen);
}
/*
* Replace instructions with better alternatives for this CPU type. This runs
* before SMP is initialized to avoid SMP problems with self modifying code.
* This implies that asymmetric systems where APs have less capabilities than
* the boot processor are not handled. Tough. Make sure you disable such
* features by hand.
*
* Marked "noinline" to cause control flow change and thus insn cache
* to refetch changed I$ lines.
*/
void __init_or_module noinline apply_alternatives(struct alt_instr *start,
struct alt_instr *end)
{
struct alt_instr *a;
u8 *instr, *replacement;
u8 insn_buff[MAX_PATCH_LEN];
DPRINTK("alt table %px, -> %px", start, end);
/*
* The scan order should be from start to end. A later scanned
* alternative code can overwrite previously scanned alternative code.
* Some kernel functions (e.g. memcpy, memset, etc) use this order to
* patch code.
*
* So be careful if you want to change the scan order to any other
* order.
*/
for (a = start; a < end; a++) {
int insn_buff_sz = 0;
instr = (u8 *)&a->instr_offset + a->instr_offset;
replacement = (u8 *)&a->repl_offset + a->repl_offset;
BUG_ON(a->instrlen > sizeof(insn_buff));
BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);
if (!boot_cpu_has(a->cpuid)) {
if (a->padlen > 1)
optimize_nops(a, instr);
continue;
}
DPRINTK("feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d), pad: %d",
a->cpuid >> 5,
a->cpuid & 0x1f,
instr, instr, a->instrlen,
replacement, a->replacementlen, a->padlen);
DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr);
DUMP_BYTES(replacement, a->replacementlen, "%px: rpl_insn: ", replacement);
memcpy(insn_buff, replacement, a->replacementlen);
insn_buff_sz = a->replacementlen;
/*
* 0xe8 is a relative jump; fix the offset.
*
* Instruction length is checked before the opcode to avoid
* accessing uninitialized bytes for zero-length replacements.
*/
if (a->replacementlen == 5 && *insn_buff == 0xe8) {
*(s32 *)(insn_buff + 1) += replacement - instr;
DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx",
*(s32 *)(insn_buff + 1),
(unsigned long)instr + *(s32 *)(insn_buff + 1) + 5);
}
if (a->replacementlen && is_jmp(replacement[0]))
recompute_jump(a, instr, replacement, insn_buff);
if (a->instrlen > a->replacementlen) {
add_nops(insn_buff + a->replacementlen,
a->instrlen - a->replacementlen);
insn_buff_sz += a->instrlen - a->replacementlen;
}
DUMP_BYTES(insn_buff, insn_buff_sz, "%px: final_insn: ", instr);
text_poke_early(instr, insn_buff, insn_buff_sz);
}
}
#ifdef CONFIG_SMP
static void alternatives_smp_lock(const s32 *start, const s32 *end,
u8 *text, u8 *text_end)
{
const s32 *poff;
for (poff = start; poff < end; poff++) {
u8 *ptr = (u8 *)poff + *poff;
if (!*poff || ptr < text || ptr >= text_end)
continue;
/* turn DS segment override prefix into lock prefix */
if (*ptr == 0x3e)
text_poke(ptr, ((unsigned char []){0xf0}), 1);
}
}
static void alternatives_smp_unlock(const s32 *start, const s32 *end,
u8 *text, u8 *text_end)
{
const s32 *poff;
for (poff = start; poff < end; poff++) {
u8 *ptr = (u8 *)poff + *poff;
if (!*poff || ptr < text || ptr >= text_end)
continue;
/* turn lock prefix into DS segment override prefix */
if (*ptr == 0xf0)
text_poke(ptr, ((unsigned char []){0x3E}), 1);
}
}
struct smp_alt_module {
/* what is this ??? */
struct module *mod;
char *name;
/* ptrs to lock prefixes */
const s32 *locks;
const s32 *locks_end;
/* .text segment, needed to avoid patching init code ;) */
u8 *text;
u8 *text_end;
struct list_head next;
};
static LIST_HEAD(smp_alt_modules);
static bool uniproc_patched = false; /* protected by text_mutex */
void __init_or_module alternatives_smp_module_add(struct module *mod,
char *name,
void *locks, void *locks_end,
void *text, void *text_end)
{
struct smp_alt_module *smp;
mutex_lock(&text_mutex);
if (!uniproc_patched)
goto unlock;
if (num_possible_cpus() == 1)
/* Don't bother remembering, we'll never have to undo it. */
goto smp_unlock;
smp = kzalloc(sizeof(*smp), GFP_KERNEL);
if (NULL == smp)
/* we'll run the (safe but slow) SMP code then ... */
goto unlock;
smp->mod = mod;
smp->name = name;
smp->locks = locks;
smp->locks_end = locks_end;
smp->text = text;
smp->text_end = text_end;
DPRINTK("locks %p -> %p, text %p -> %p, name %s\n",
smp->locks, smp->locks_end,
smp->text, smp->text_end, smp->name);
list_add_tail(&smp->next, &smp_alt_modules);
smp_unlock:
alternatives_smp_unlock(locks, locks_end, text, text_end);
unlock:
mutex_unlock(&text_mutex);
}
void __init_or_module alternatives_smp_module_del(struct module *mod)
{
struct smp_alt_module *item;
mutex_lock(&text_mutex);
list_for_each_entry(item, &smp_alt_modules, next) {
if (mod != item->mod)
continue;
list_del(&item->next);
kfree(item);
break;
}
mutex_unlock(&text_mutex);
}
void alternatives_enable_smp(void)
{
struct smp_alt_module *mod;
/* Why bother if there are no other CPUs? */
BUG_ON(num_possible_cpus() == 1);
mutex_lock(&text_mutex);
if (uniproc_patched) {
pr_info("switching to SMP code\n");
BUG_ON(num_online_cpus() != 1);
clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
list_for_each_entry(mod, &smp_alt_modules, next)
alternatives_smp_lock(mod->locks, mod->locks_end,
mod->text, mod->text_end);
uniproc_patched = false;
}
mutex_unlock(&text_mutex);
}
/*
* Return 1 if the address range is reserved for SMP-alternatives.
* Must hold text_mutex.
*/
int alternatives_text_reserved(void *start, void *end)
{
struct smp_alt_module *mod;
const s32 *poff;
u8 *text_start = start;
u8 *text_end = end;
lockdep_assert_held(&text_mutex);
list_for_each_entry(mod, &smp_alt_modules, next) {
if (mod->text > text_end || mod->text_end < text_start)
continue;
for (poff = mod->locks; poff < mod->locks_end; poff++) {
const u8 *ptr = (const u8 *)poff + *poff;
if (text_start <= ptr && text_end > ptr)
return 1;
}
}
return 0;
}
#endif /* CONFIG_SMP */
#ifdef CONFIG_PARAVIRT
void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
struct paravirt_patch_site *end)
{
struct paravirt_patch_site *p;
char insn_buff[MAX_PATCH_LEN];
for (p = start; p < end; p++) {
unsigned int used;
BUG_ON(p->len > MAX_PATCH_LEN);
/* prep the buffer with the original instructions */
memcpy(insn_buff, p->instr, p->len);
used = pv_ops.init.patch(p->type, insn_buff, (unsigned long)p->instr, p->len);
BUG_ON(used > p->len);
/* Pad the rest with nops */
add_nops(insn_buff + used, p->len - used);
text_poke_early(p->instr, insn_buff, p->len);
}
}
extern struct paravirt_patch_site __start_parainstructions[],
__stop_parainstructions[];
#endif /* CONFIG_PARAVIRT */
/*
* Self-test for the INT3 based CALL emulation code.
*
* This exercises int3_emulate_call() to make sure INT3 pt_regs are set up
* properly and that there is a stack gap between the INT3 frame and the
* previous context. Without this gap doing a virtual PUSH on the interrupted
* stack would corrupt the INT3 IRET frame.
*
* See entry_{32,64}.S for more details.
*/
/*
* We define the int3_magic() function in assembly to control the calling
* convention such that we can 'call' it from assembly.
*/
extern void int3_magic(unsigned int *ptr); /* defined in asm */
asm (
" .pushsection .init.text, \"ax\", @progbits\n"
" .type int3_magic, @function\n"
"int3_magic:\n"
" movl $1, (%" _ASM_ARG1 ")\n"
" ret\n"
" .size int3_magic, .-int3_magic\n"
" .popsection\n"
);
extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */
static int __init
int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
{
struct die_args *args = data;
struct pt_regs *regs = args->regs;
if (!regs || user_mode(regs))
return NOTIFY_DONE;
if (val != DIE_INT3)
return NOTIFY_DONE;
if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip)
return NOTIFY_DONE;
int3_emulate_call(regs, (unsigned long)&int3_magic);
return NOTIFY_STOP;
}
static void __init int3_selftest(void)
{
static __initdata struct notifier_block int3_exception_nb = {
.notifier_call = int3_exception_notify,
.priority = INT_MAX-1, /* last */
};
unsigned int val = 0;
BUG_ON(register_die_notifier(&int3_exception_nb));
/*
* Basically: int3_magic(&val); but really complicated :-)
*
* Stick the address of the INT3 instruction into int3_selftest_ip,
* then trigger the INT3, padded with NOPs to match a CALL instruction
* length.
*/
asm volatile ("1: int3; nop; nop; nop; nop\n\t"
".pushsection .init.data,\"aw\"\n\t"
".align " __ASM_SEL(4, 8) "\n\t"
".type int3_selftest_ip, @object\n\t"
".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t"
"int3_selftest_ip:\n\t"
__ASM_SEL(.long, .quad) " 1b\n\t"
".popsection\n\t"
: ASM_CALL_CONSTRAINT
: __ASM_SEL_RAW(a, D) (&val)
: "memory");
BUG_ON(val != 1);
unregister_die_notifier(&int3_exception_nb);
}
void __init alternative_instructions(void)
{
int3_selftest();
/*
* The patching is not fully atomic, so try to avoid local
* interruptions that might execute the to be patched code.
* Other CPUs are not running.
*/
stop_nmi();
/*
* Don't stop machine check exceptions while patching.
* MCEs only happen when something got corrupted and in this
* case we must do something about the corruption.
* Ignoring it is worse than a unlikely patching race.
* Also machine checks tend to be broadcast and if one CPU
* goes into machine check the others follow quickly, so we don't
* expect a machine check to cause undue problems during to code
* patching.
*/
apply_alternatives(__alt_instructions, __alt_instructions_end);
#ifdef CONFIG_SMP
/* Patch to UP if other cpus not imminent. */
if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) {
uniproc_patched = true;
alternatives_smp_module_add(NULL, "core kernel",
__smp_locks, __smp_locks_end,
_text, _etext);
}
if (!uniproc_patched || num_possible_cpus() == 1) {
free_init_pages("SMP alternatives",
(unsigned long)__smp_locks,
(unsigned long)__smp_locks_end);
}
#endif
apply_paravirt(__parainstructions, __parainstructions_end);
restart_nmi();
alternatives_patched = 1;
}
/**
* text_poke_early - Update instructions on a live kernel at boot time
* @addr: address to modify
* @opcode: source of the copy
* @len: length to copy
*
* When you use this code to patch more than one byte of an instruction
* you need to make sure that other CPUs cannot execute this code in parallel.
* Also no thread must be currently preempted in the middle of these
* instructions. And on the local CPU you need to be protected again NMI or MCE
* handlers seeing an inconsistent instruction while you patch.
*/
void __init_or_module text_poke_early(void *addr, const void *opcode,
size_t len)
{
unsigned long flags;
if (boot_cpu_has(X86_FEATURE_NX) &&
is_module_text_address((unsigned long)addr)) {
/*
* Modules text is marked initially as non-executable, so the
* code cannot be running and speculative code-fetches are
* prevented. Just change the code.
*/
memcpy(addr, opcode, len);
} else {
local_irq_save(flags);
memcpy(addr, opcode, len);
local_irq_restore(flags);
sync_core();
/*
* Could also do a CLFLUSH here to speed up CPU recovery; but
* that causes hangs on some VIA CPUs.
*/
}
}
__ro_after_init struct mm_struct *poking_mm;
__ro_after_init unsigned long poking_addr;
static void *__text_poke(void *addr, const void *opcode, size_t len)
{
bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;
struct page *pages[2] = {NULL};
temp_mm_state_t prev;
unsigned long flags;
pte_t pte, *ptep;
spinlock_t *ptl;
pgprot_t pgprot;
/*
* While boot memory allocator is running we cannot use struct pages as
* they are not yet initialized. There is no way to recover.
*/
BUG_ON(!after_bootmem);
if (!core_kernel_text((unsigned long)addr)) {
pages[0] = vmalloc_to_page(addr);
if (cross_page_boundary)
pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
} else {
pages[0] = virt_to_page(addr);
WARN_ON(!PageReserved(pages[0]));
if (cross_page_boundary)
pages[1] = virt_to_page(addr + PAGE_SIZE);
}
/*
* If something went wrong, crash and burn since recovery paths are not
* implemented.
*/
BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
local_irq_save(flags);
/*
* Map the page without the global bit, as TLB flushing is done with
* flush_tlb_mm_range(), which is intended for non-global PTEs.
*/
pgprot = __pgprot(pgprot_val(PAGE_KERNEL) & ~_PAGE_GLOBAL);
/*
* The lock is not really needed, but this allows to avoid open-coding.
*/
ptep = get_locked_pte(poking_mm, poking_addr, &ptl);
/*
* This must not fail; preallocated in poking_init().
*/
VM_BUG_ON(!ptep);
pte = mk_pte(pages[0], pgprot);
set_pte_at(poking_mm, poking_addr, ptep, pte);
if (cross_page_boundary) {
pte = mk_pte(pages[1], pgprot);
set_pte_at(poking_mm, poking_addr + PAGE_SIZE, ptep + 1, pte);
}
/*
* Loading the temporary mm behaves as a compiler barrier, which
* guarantees that the PTE will be set at the time memcpy() is done.
*/
prev = use_temporary_mm(poking_mm);
kasan_disable_current();
memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len);
kasan_enable_current();
/*
* Ensure that the PTE is only cleared after the instructions of memcpy
* were issued by using a compiler barrier.
*/
barrier();
pte_clear(poking_mm, poking_addr, ptep);
if (cross_page_boundary)
pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep + 1);
/*
* Loading the previous page-table hierarchy requires a serializing
* instruction that already allows the core to see the updated version.
* Xen-PV is assumed to serialize execution in a similar manner.
*/
unuse_temporary_mm(prev);
/*
* Flushing the TLB might involve IPIs, which would require enabled
* IRQs, but not if the mm is not used, as it is in this point.
*/
flush_tlb_mm_range(poking_mm, poking_addr, poking_addr +
(cross_page_boundary ? 2 : 1) * PAGE_SIZE,
PAGE_SHIFT, false);
/*
* If the text does not match what we just wrote then something is
* fundamentally screwy; there's nothing we can really do about that.
*/
BUG_ON(memcmp(addr, opcode, len));
pte_unmap_unlock(ptep, ptl);
local_irq_restore(flags);
return addr;
}
/**
* text_poke - Update instructions on a live kernel
* @addr: address to modify
* @opcode: source of the copy
* @len: length to copy
*
* Only atomic text poke/set should be allowed when not doing early patching.
* It means the size must be writable atomically and the address must be aligned
* in a way that permits an atomic write. It also makes sure we fit on a single
* page.
*
* Note that the caller must ensure that if the modified code is part of a
* module, the module would not be removed during poking. This can be achieved
* by registering a module notifier, and ordering module removal and patching
* trough a mutex.
*/
void *text_poke(void *addr, const void *opcode, size_t len)
{
lockdep_assert_held(&text_mutex);
return __text_poke(addr, opcode, len);
}
/**
* text_poke_kgdb - Update instructions on a live kernel by kgdb
* @addr: address to modify
* @opcode: source of the copy
* @len: length to copy
*
* Only atomic text poke/set should be allowed when not doing early patching.
* It means the size must be writable atomically and the address must be aligned
* in a way that permits an atomic write. It also makes sure we fit on a single
* page.
*
* Context: should only be used by kgdb, which ensures no other core is running,
* despite the fact it does not hold the text_mutex.
*/
void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
{
return __text_poke(addr, opcode, len);
}
static void do_sync_core(void *info)
{
sync_core();
}
static struct bp_patching_desc {
struct text_poke_loc *vec;
int nr_entries;
} bp_patching;
static int patch_cmp(const void *key, const void *elt)
{
struct text_poke_loc *tp = (struct text_poke_loc *) elt;
if (key < tp->addr)
return -1;
if (key > tp->addr)
return 1;
return 0;
}
NOKPROBE_SYMBOL(patch_cmp);
int poke_int3_handler(struct pt_regs *regs)
{
struct text_poke_loc *tp;
unsigned char int3 = 0xcc;
void *ip;
/*
* Having observed our INT3 instruction, we now must observe
* bp_patching.nr_entries.
*
* nr_entries != 0 INT3
* WMB RMB
* write INT3 if (nr_entries)
*
* Idem for other elements in bp_patching.
*/
smp_rmb();
if (likely(!bp_patching.nr_entries))
return 0;
if (user_mode(regs))
return 0;
/*
* Discount the sizeof(int3). See text_poke_bp_batch().
*/
ip = (void *) regs->ip - sizeof(int3);
/*
* Skip the binary search if there is a single member in the vector.
*/
if (unlikely(bp_patching.nr_entries > 1)) {
tp = bsearch(ip, bp_patching.vec, bp_patching.nr_entries,
sizeof(struct text_poke_loc),
patch_cmp);
if (!tp)
return 0;
} else {
tp = bp_patching.vec;
if (tp->addr != ip)
return 0;
}
/* set up the specified breakpoint detour */
regs->ip = (unsigned long) tp->detour;
return 1;
}
NOKPROBE_SYMBOL(poke_int3_handler);
/**
* text_poke_bp_batch() -- update instructions on live kernel on SMP
* @tp: vector of instructions to patch
* @nr_entries: number of entries in the vector
*
* Modify multi-byte instruction by using int3 breakpoint on SMP.
* We completely avoid stop_machine() here, and achieve the
* synchronization using int3 breakpoint.
*
* The way it is done:
* - For each entry in the vector:
* - add a int3 trap to the address that will be patched
* - sync cores
* - For each entry in the vector:
* - update all but the first byte of the patched range
* - sync cores
* - For each entry in the vector:
* - replace the first byte (int3) by the first byte of
* replacing opcode
* - sync cores
*/
void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
{
int patched_all_but_first = 0;
unsigned char int3 = 0xcc;
unsigned int i;
lockdep_assert_held(&text_mutex);
bp_patching.vec = tp;
bp_patching.nr_entries = nr_entries;
/*
* Corresponding read barrier in int3 notifier for making sure the
* nr_entries and handler are correctly ordered wrt. patching.
*/
smp_wmb();
/*
* First step: add a int3 trap to the address that will be patched.
*/
for (i = 0; i < nr_entries; i++)
text_poke(tp[i].addr, &int3, sizeof(int3));
on_each_cpu(do_sync_core, NULL, 1);
/*
* Second step: update all but the first byte of the patched range.
*/
for (i = 0; i < nr_entries; i++) {
if (tp[i].len - sizeof(int3) > 0) {
text_poke((char *)tp[i].addr + sizeof(int3),
(const char *)tp[i].opcode + sizeof(int3),
tp[i].len - sizeof(int3));
patched_all_but_first++;
}
}
if (patched_all_but_first) {
/*
* According to Intel, this core syncing is very likely
* not necessary and we'd be safe even without it. But
* better safe than sorry (plus there's not only Intel).
*/
on_each_cpu(do_sync_core, NULL, 1);
}
/*
* Third step: replace the first byte (int3) by the first byte of
* replacing opcode.
*/
for (i = 0; i < nr_entries; i++)
text_poke(tp[i].addr, tp[i].opcode, sizeof(int3));
on_each_cpu(do_sync_core, NULL, 1);
/*
* sync_core() implies an smp_mb() and orders this store against
* the writing of the new instruction.
*/
bp_patching.vec = NULL;
bp_patching.nr_entries = 0;
}
/**
* text_poke_bp() -- update instructions on live kernel on SMP
* @addr: address to patch
* @opcode: opcode of new instruction
* @len: length to copy
* @handler: address to jump to when the temporary breakpoint is hit
*
* Update a single instruction with the vector in the stack, avoiding
* dynamically allocated memory. This function should be used when it is
* not possible to allocate memory.
*/
void text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
{
struct text_poke_loc tp = {
.detour = handler,
.addr = addr,
.len = len,
};
if (len > POKE_MAX_OPCODE_SIZE) {
WARN_ONCE(1, "len is larger than %d\n", POKE_MAX_OPCODE_SIZE);
return;
}
memcpy((void *)tp.opcode, opcode, len);
text_poke_bp_batch(&tp, 1);
}
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