alternative.c

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/kprobes.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <asm/alternative.h>
#include <asm/sections.h>
#include <asm/pgtable.h>
#include <asm/mce.h>
#include <asm/nmi.h>
#include <asm/vsyscall.h>
#include <asm/cacheflush.h>
#include <asm/io.h>

#define MAX_PATCH_LEN (255-1)

#ifdef CONFIG_HOTPLUG_CPU
static int smp_alt_once;

static int __init bootonly(char *str)
{
	smp_alt_once = 1;
	return 1;
}
__setup("smp-alt-boot", bootonly);
#else
#define smp_alt_once 1
#endif

static int 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);

#ifdef CONFIG_PARAVIRT
static int noreplace_paravirt = 0;

static int __init setup_noreplace_paravirt(char *str)
{
	noreplace_paravirt = 1;
	return 1;
}
__setup("noreplace-paravirt", setup_noreplace_paravirt);
#endif

#define DPRINTK(fmt, args...) if (debug_alternative) \
	printk(KERN_DEBUG fmt, args)

#ifdef GENERIC_NOP1
/* Use inline assembly to define this because the nops are defined
   as inline assembly strings in the include files and we cannot
   get them easily into strings. */
asm("\t.section .rodata, \"a\"\nintelnops: "
	GENERIC_NOP1 GENERIC_NOP2 GENERIC_NOP3 GENERIC_NOP4 GENERIC_NOP5 GENERIC_NOP6
	GENERIC_NOP7 GENERIC_NOP8
    "\t.previous");
extern const unsigned char intelnops[];
static const unsigned char *const intel_nops[ASM_NOP_MAX+1] = {
	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,
};
#endif

#ifdef K8_NOP1
asm("\t.section .rodata, \"a\"\nk8nops: "
	K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
	K8_NOP7 K8_NOP8
    "\t.previous");
extern const unsigned char k8nops[];
static const unsigned char *const k8_nops[ASM_NOP_MAX+1] = {
	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,
};
#endif

#ifdef K7_NOP1
asm("\t.section .rodata, \"a\"\nk7nops: "
	K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
	K7_NOP7 K7_NOP8
    "\t.previous");
extern const unsigned char k7nops[];
static const unsigned char *const k7_nops[ASM_NOP_MAX+1] = {
	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,
};
#endif

#ifdef P6_NOP1
asm("\t.section .rodata, \"a\"\np6nops: "
	P6_NOP1 P6_NOP2 P6_NOP3 P6_NOP4 P6_NOP5 P6_NOP6
	P6_NOP7 P6_NOP8
    "\t.previous");
extern const unsigned char p6nops[];
static const unsigned char *const p6_nops[ASM_NOP_MAX+1] = {
	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,
};
#endif

#ifdef CONFIG_X86_64

extern char __vsyscall_0;
const unsigned char *const *find_nop_table(void)
{
	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
	    boot_cpu_has(X86_FEATURE_NOPL))
		return p6_nops;
	else
		return k8_nops;
}

#else /* CONFIG_X86_64 */

const unsigned char *const *find_nop_table(void)
{
	if (boot_cpu_has(X86_FEATURE_K8))
		return k8_nops;
	else if (boot_cpu_has(X86_FEATURE_K7))
		return k7_nops;
	else if (boot_cpu_has(X86_FEATURE_NOPL))
		return p6_nops;
	else
		return intel_nops;
}

#endif /* CONFIG_X86_64 */

/* Use this to add nops to a buffer, then text_poke the whole buffer. */
void add_nops(void *insns, unsigned int len)
{
	const unsigned char *const *noptable = find_nop_table();

	while (len > 0) {
		unsigned int noplen = len;
		if (noplen > ASM_NOP_MAX)
			noplen = ASM_NOP_MAX;
		memcpy(insns, noptable[noplen], noplen);
		insns += noplen;
		len -= noplen;
	}
}
EXPORT_SYMBOL_GPL(add_nops);

extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern u8 *__smp_locks[], *__smp_locks_end[];

/* 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 assymetric systems where
   APs have less capabilities than the boot processor are not handled.
   Tough. Make sure you disable such features by hand. */

void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
{
	struct alt_instr *a;
	char insnbuf[MAX_PATCH_LEN];

	DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
	for (a = start; a < end; a++) {
		u8 *instr = a->instr;
		BUG_ON(a->replacementlen > a->instrlen);
		BUG_ON(a->instrlen > sizeof(insnbuf));
		if (!boot_cpu_has(a->cpuid))
			continue;
#ifdef CONFIG_X86_64
		/* vsyscall code is not mapped yet. resolve it manually. */
		if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
			instr = __va(instr - (u8*)VSYSCALL_START + (u8*)__pa_symbol(&__vsyscall_0));
			DPRINTK("%s: vsyscall fixup: %p => %p\n",
				__func__, a->instr, instr);
		}
#endif
		memcpy(insnbuf, a->replacement, a->replacementlen);
		add_nops(insnbuf + a->replacementlen,
			 a->instrlen - a->replacementlen);
		text_poke_early(instr, insnbuf, a->instrlen);
	}
}

#ifdef CONFIG_SMP

static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
	u8 **ptr;

	for (ptr = start; ptr < end; ptr++) {
		if (*ptr < text)
			continue;
		if (*ptr > text_end)
			continue;
		/* turn DS segment override prefix into lock prefix */
		text_poke(*ptr, ((unsigned char []){0xf0}), 1);
	};
}

static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
	u8 **ptr;

	if (noreplace_smp)
		return;

	for (ptr = start; ptr < end; ptr++) {
		if (*ptr < text)
			continue;
		if (*ptr > text_end)
			continue;
		/* turn lock prefix into DS segment override prefix */
		text_poke(*ptr, ((unsigned char []){0x3E}), 1);
	};
}

struct smp_alt_module {
	/* what is this ??? */
	struct module	*mod;
	char		*name;

	/* ptrs to lock prefixes */
	u8		**locks;
	u8		**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 DEFINE_MUTEX(smp_alt);
static int smp_mode = 1;	/* protected by smp_alt */

void alternatives_smp_module_add(struct module *mod, char *name,
				 void *locks, void *locks_end,
				 void *text,  void *text_end)
{
	struct smp_alt_module *smp;

	if (noreplace_smp)
		return;

	if (smp_alt_once) {
		if (boot_cpu_has(X86_FEATURE_UP))
			alternatives_smp_unlock(locks, locks_end,
						text, text_end);
		return;
	}

	smp = kzalloc(sizeof(*smp), GFP_KERNEL);
	if (NULL == smp)
		return; /* we'll run the (safe but slow) SMP code then ... */

	smp->mod	= mod;
	smp->name	= name;
	smp->locks	= locks;
	smp->locks_end	= locks_end;
	smp->text	= text;
	smp->text_end	= text_end;
	DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
		__func__, smp->locks, smp->locks_end,
		smp->text, smp->text_end, smp->name);

	mutex_lock(&smp_alt);
	list_add_tail(&smp->next, &smp_alt_modules);
	if (boot_cpu_has(X86_FEATURE_UP))
		alternatives_smp_unlock(smp->locks, smp->locks_end,
					smp->text, smp->text_end);
	mutex_unlock(&smp_alt);
}

void alternatives_smp_module_del(struct module *mod)
{
	struct smp_alt_module *item;

	if (smp_alt_once || noreplace_smp)
		return;

	mutex_lock(&smp_alt);
	list_for_each_entry(item, &smp_alt_modules, next) {
		if (mod != item->mod)
			continue;
		list_del(&item->next);
		mutex_unlock(&smp_alt);
		DPRINTK("%s: %s\n", __func__, item->name);
		kfree(item);
		return;
	}
	mutex_unlock(&smp_alt);
}

void alternatives_smp_switch(int smp)
{
	struct smp_alt_module *mod;

#ifdef CONFIG_LOCKDEP
	/*
	 * Older binutils section handling bug prevented
	 * alternatives-replacement from working reliably.
	 *
	 * If this still occurs then you should see a hang
	 * or crash shortly after this line:
	 */
	printk("lockdep: fixing up alternatives.\n");
#endif

	if (noreplace_smp || smp_alt_once)
		return;
	BUG_ON(!smp && (num_online_cpus() > 1));

	mutex_lock(&smp_alt);

	/*
	 * Avoid unnecessary switches because it forces JIT based VMs to
	 * throw away all cached translations, which can be quite costly.
	 */
	if (smp == smp_mode) {
		/* nothing */
	} else if (smp) {
		printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
		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);
	} else {
		printk(KERN_INFO "SMP alternatives: switching to UP code\n");
		set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
		set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
		list_for_each_entry(mod, &smp_alt_modules, next)
			alternatives_smp_unlock(mod->locks, mod->locks_end,
						mod->text, mod->text_end);
	}
	smp_mode = smp;
	mutex_unlock(&smp_alt);
}

#endif

#ifdef CONFIG_PARAVIRT
void apply_paravirt(struct paravirt_patch_site *start,
		    struct paravirt_patch_site *end)
{
	struct paravirt_patch_site *p;
	char insnbuf[MAX_PATCH_LEN];

	if (noreplace_paravirt)
		return;

	for (p = start; p < end; p++) {
		unsigned int used;

		BUG_ON(p->len > MAX_PATCH_LEN);
		/* prep the buffer with the original instructions */
		memcpy(insnbuf, p->instr, p->len);
		used = pv_init_ops.patch(p->instrtype, p->clobbers, insnbuf,
					 (unsigned long)p->instr, p->len);

		BUG_ON(used > p->len);

		/* Pad the rest with nops */
		add_nops(insnbuf + used, p->len - used);
		text_poke_early(p->instr, insnbuf, p->len);
	}
}
extern struct paravirt_patch_site __start_parainstructions[],
	__stop_parainstructions[];
#endif	/* CONFIG_PARAVIRT */

void __init alternative_instructions(void)
{
	/* 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);

	/* switch to patch-once-at-boottime-only mode and free the
	 * tables in case we know the number of CPUs will never ever
	 * change */
#ifdef CONFIG_HOTPLUG_CPU
	if (num_possible_cpus() < 2)
		smp_alt_once = 1;
#endif

#ifdef CONFIG_SMP
	if (smp_alt_once) {
		if (1 == num_possible_cpus()) {
			printk(KERN_INFO "SMP alternatives: switching to UP code\n");
			set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
			set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);

			alternatives_smp_unlock(__smp_locks, __smp_locks_end,
						_text, _etext);
		}
	} else {
		alternatives_smp_module_add(NULL, "core kernel",
					    __smp_locks, __smp_locks_end,
					    _text, _etext);

		/* Only switch to UP mode if we don't immediately boot others */
		if (num_present_cpus() == 1 || setup_max_cpus <= 1)
			alternatives_smp_switch(0);
	}
#endif
 	apply_paravirt(__parainstructions, __parainstructions_end);

	if (smp_alt_once)
		free_init_pages("SMP alternatives",
				(unsigned long)__smp_locks,
				(unsigned long)__smp_locks_end);

	restart_nmi();
}

/**
 * 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 *text_poke_early(void *addr, const void *opcode, size_t len)
{
	unsigned long flags;
	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. */
	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.
 */
void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
{
	char *vaddr;
	int nr_pages = 2;
	struct page *pages[2];
	int i;

	might_sleep();
	if (!core_kernel_text((unsigned long)addr)) {
		pages[0] = vmalloc_to_page(addr);
		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
	} else {
		pages[0] = virt_to_page(addr);
		WARN_ON(!PageReserved(pages[0]));
		pages[1] = virt_to_page(addr + PAGE_SIZE);
	}
	BUG_ON(!pages[0]);
	if (!pages[1])
		nr_pages = 1;
	vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
	BUG_ON(!vaddr);
	local_irq_disable();
	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
	local_irq_enable();
	vunmap(vaddr);
	sync_core();
	/* Could also do a CLFLUSH here to speed up CPU recovery; but
	   that causes hangs on some VIA CPUs. */
	for (i = 0; i < len; i++)
		BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
	return addr;
}