Commit e587cadd authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Ingo Molnar
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x86: enhance DEBUG_RODATA support - alternatives



Fix a memcpy that should be a text_poke (in apply_alternatives).

Use kernel_wp_save/kernel_wp_restore in text_poke to support DEBUG_RODATA
correctly and so the CPU HOTPLUG special case can be removed.

Add text_poke_early, for alternatives and paravirt boot-time and module load
time patching.

Changelog:

- Fix text_set and text_poke alignment check (mixed up bitwise and and or)
- Remove text_set
- Export add_nops, so it can be used by others.
- Document text_poke_early.
- Remove clflush, since it breaks some VIA architectures and is not strictly
  necessary.
- Add kerneldoc to text_poke and text_poke_early.
- Create a second vmap instead of using the WP bit to support Xen and VMI.
- Move local_irq disable within text_poke and text_poke_early to be able to
  be sleepable in these functions.
Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Andi Kleen <andi@firstfloor.org>
CC: pageexec@freemail.hu
CC: H. Peter Anvin <hpa@zytor.com>
CC: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 77bf90ed
......@@ -11,6 +11,8 @@
#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)
......@@ -177,7 +179,7 @@ static const unsigned char*const * find_nop_table(void)
#endif /* CONFIG_X86_64 */
/* Use this to add nops to a buffer, then text_poke the whole buffer. */
static void add_nops(void *insns, unsigned int len)
void add_nops(void *insns, unsigned int len)
{
const unsigned char *const *noptable = find_nop_table();
......@@ -190,6 +192,7 @@ static void add_nops(void *insns, unsigned int len)
len -= noplen;
}
}
EXPORT_SYMBOL_GPL(add_nops);
extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern u8 *__smp_locks[], *__smp_locks_end[];
......@@ -223,7 +226,7 @@ void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
memcpy(insnbuf, a->replacement, a->replacementlen);
add_nops(insnbuf + a->replacementlen,
a->instrlen - a->replacementlen);
text_poke(instr, insnbuf, a->instrlen);
text_poke_early(instr, insnbuf, a->instrlen);
}
}
......@@ -284,7 +287,6 @@ void alternatives_smp_module_add(struct module *mod, char *name,
void *text, void *text_end)
{
struct smp_alt_module *smp;
unsigned long flags;
if (noreplace_smp)
return;
......@@ -310,39 +312,37 @@ void alternatives_smp_module_add(struct module *mod, char *name,
__func__, smp->locks, smp->locks_end,
smp->text, smp->text_end, smp->name);
spin_lock_irqsave(&smp_alt, flags);
spin_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);
spin_unlock_irqrestore(&smp_alt, flags);
spin_unlock(&smp_alt);
}
void alternatives_smp_module_del(struct module *mod)
{
struct smp_alt_module *item;
unsigned long flags;
if (smp_alt_once || noreplace_smp)
return;
spin_lock_irqsave(&smp_alt, flags);
spin_lock(&smp_alt);
list_for_each_entry(item, &smp_alt_modules, next) {
if (mod != item->mod)
continue;
list_del(&item->next);
spin_unlock_irqrestore(&smp_alt, flags);
spin_unlock(&smp_alt);
DPRINTK("%s: %s\n", __func__, item->name);
kfree(item);
return;
}
spin_unlock_irqrestore(&smp_alt, flags);
spin_unlock(&smp_alt);
}
void alternatives_smp_switch(int smp)
{
struct smp_alt_module *mod;
unsigned long flags;
#ifdef CONFIG_LOCKDEP
/*
......@@ -359,7 +359,7 @@ void alternatives_smp_switch(int smp)
return;
BUG_ON(!smp && (num_online_cpus() > 1));
spin_lock_irqsave(&smp_alt, flags);
spin_lock(&smp_alt);
/*
* Avoid unnecessary switches because it forces JIT based VMs to
......@@ -383,7 +383,7 @@ void alternatives_smp_switch(int smp)
mod->text, mod->text_end);
}
smp_mode = smp;
spin_unlock_irqrestore(&smp_alt, flags);
spin_unlock(&smp_alt);
}
#endif
......@@ -411,7 +411,7 @@ void apply_paravirt(struct paravirt_patch_site *start,
/* Pad the rest with nops */
add_nops(insnbuf + used, p->len - used);
text_poke(p->instr, insnbuf, p->len);
text_poke_early(p->instr, insnbuf, p->len);
}
}
extern struct paravirt_patch_site __start_parainstructions[],
......@@ -420,8 +420,6 @@ extern struct paravirt_patch_site __start_parainstructions[],
void __init alternative_instructions(void)
{
unsigned long flags;
/* 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. */
......@@ -430,7 +428,6 @@ void __init alternative_instructions(void)
stop_mce();
#endif
local_irq_save(flags);
apply_alternatives(__alt_instructions, __alt_instructions_end);
/* switch to patch-once-at-boottime-only mode and free the
......@@ -462,7 +459,6 @@ void __init alternative_instructions(void)
}
#endif
apply_paravirt(__parainstructions, __parainstructions_end);
local_irq_restore(flags);
if (smp_alt_once)
free_init_pages("SMP alternatives",
......@@ -475,18 +471,64 @@ void __init alternative_instructions(void)
#endif
}
/*
* Warning:
/**
* 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.
* 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 __kprobes text_poke(void *addr, unsigned char *opcode, int len)
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)
{
unsigned long flags;
char *vaddr;
int nr_pages = 2;
BUG_ON(len > sizeof(long));
BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
- ((long)addr & ~(sizeof(long) - 1)));
{
struct page *pages[2] = { virt_to_page(addr),
virt_to_page(addr + PAGE_SIZE) };
if (!pages[1])
nr_pages = 1;
vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
BUG_ON(!vaddr);
local_irq_save(flags);
memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
local_irq_restore(flags);
vunmap(vaddr);
}
sync_core();
/* Could also do a CLFLUSH here to speed up CPU recovery; but
that causes hangs on some VIA CPUs. */
return addr;
}
......@@ -156,6 +156,27 @@ apply_paravirt(struct paravirt_patch_site *start,
#define __parainstructions_end NULL
#endif
extern void text_poke(void *addr, unsigned char *opcode, int len);
extern void add_nops(void *insns, unsigned int len);
/*
* Clear and restore the kernel write-protection flag on the local CPU.
* Allows the kernel to edit read-only pages.
* Side-effect: any interrupt handler running between save and restore will have
* the ability to write to read-only pages.
*
* Warning:
* Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
* no thread can be preempted in the instructions being modified (no iret to an
* invalid instruction possible) or if the instructions are changed from a
* consistent state to another consistent state atomically.
* More care must be taken when modifying code in the SMP case because of
* Intel's errata.
* On the local CPU you need to be protected again NMI or MCE handlers seeing an
* inconsistent instruction while you patch.
* The _early version expects the memory to already be RW.
*/
extern void *text_poke(void *addr, const void *opcode, size_t len);
extern void *text_poke_early(void *addr, const void *opcode, size_t len);
#endif /* _ASM_X86_ALTERNATIVE_H */
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