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Commit ac61a757 authored by Vegard Nossum's avatar Vegard Nossum
Browse files

kmemcheck: add opcode self-testing at boot 



We've had some troubles in the past with weird instructions. This
patch adds a self-test framework which can be used to verify that
a certain set of opcodes are decoded correctly. Of course, the
opcodes which are not tested can still give the wrong results.

In short, this is just a safeguard to catch unintentional changes
in the opcode decoder. It does not mean that errors can't still
occur!

[rebased for mainline inclusion]
Signed-off-by: default avatarVegard Nossum <vegard.nossum@gmail.com>
parent eb63657e

arch/x86/mm/kmemcheck/Makefile

+1 −1
Original line number Diff line number Diff line 
obj-y := error.o kmemcheck.o opcode.o pte.o shadow.o
 
obj-y := error.o kmemcheck.o opcode.o pte.o selftest.o shadow.o

arch/x86/mm/kmemcheck/kmemcheck.c

+9 −16
Original line number Diff line number Diff line
@@ -29,8 +29,10 @@ 
#include "error.h"

#include "opcode.h"

#include "pte.h"

#include "selftest.h"

#include "shadow.h"





#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT

#  define KMEMCHECK_ENABLED 0

#endif
@@ -47,8 +49,6 @@ int kmemcheck_enabled = KMEMCHECK_ENABLED; 


int __init kmemcheck_init(void)

{

	printk(KERN_INFO "kmemcheck: Initialized\n");



#ifdef CONFIG_SMP

	/*

	 * Limit SMP to use a single CPU. We rely on the fact that this code
@@ -61,25 +61,18 @@ int __init kmemcheck_init(void) 
	}

#endif



	if (!kmemcheck_selftest()) {

		printk(KERN_INFO "kmemcheck: self-tests failed; disabling\n");

		kmemcheck_enabled = 0;

		return -EINVAL;

	}



	printk(KERN_INFO "kmemcheck: Initialized\n");

	return 0;

}



early_initcall(kmemcheck_init);



#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT

#  define KMEMCHECK_ENABLED 0

#endif



#ifdef CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT

#  define KMEMCHECK_ENABLED 1

#endif



#ifdef CONFIG_KMEMCHECK_ONESHOT_BY_DEFAULT

#  define KMEMCHECK_ENABLED 2

#endif



int kmemcheck_enabled = KMEMCHECK_ENABLED;



/*

 * We need to parse the kmemcheck= option before any memory is allocated.

 */

arch/x86/mm/kmemcheck/selftest.c

0 → 100644
+69 −0
Original line number Diff line number Diff line 
#include <linux/kernel.h>



#include "opcode.h"

#include "selftest.h"



struct selftest_opcode {

	unsigned int expected_size;

	const uint8_t *insn;

	const char *desc;

};



static const struct selftest_opcode selftest_opcodes[] = {

	/* REP MOVS */

	{1, "\xf3\xa4", 		"rep movsb <mem8>, <mem8>"},

	{4, "\xf3\xa5",			"rep movsl <mem32>, <mem32>"},



	/* MOVZX / MOVZXD */

	{1, "\x66\x0f\xb6\x51\xf8",	"movzwq <mem8>, <reg16>"},

	{1, "\x0f\xb6\x51\xf8",		"movzwq <mem8>, <reg32>"},



	/* MOVSX / MOVSXD */

	{1, "\x66\x0f\xbe\x51\xf8",	"movswq <mem8>, <reg16>"},

	{1, "\x0f\xbe\x51\xf8",		"movswq <mem8>, <reg32>"},



#ifdef CONFIG_X86_64

	/* MOVZX / MOVZXD */

	{1, "\x49\x0f\xb6\x51\xf8",	"movzbq <mem8>, <reg64>"},

	{2, "\x49\x0f\xb7\x51\xf8",	"movzbq <mem16>, <reg64>"},



	/* MOVSX / MOVSXD */

	{1, "\x49\x0f\xbe\x51\xf8",	"movsbq <mem8>, <reg64>"},

	{2, "\x49\x0f\xbf\x51\xf8",	"movsbq <mem16>, <reg64>"},

	{4, "\x49\x63\x51\xf8",		"movslq <mem32>, <reg64>"},

#endif

};



static bool selftest_opcode_one(const struct selftest_opcode *op)

{

	unsigned size;



	kmemcheck_opcode_decode(op->insn, &size);



	if (size == op->expected_size)

		return true;



	printk(KERN_WARNING "kmemcheck: opcode %s: expected size %d, got %d\n",

		op->desc, op->expected_size, size);

	return false;

}



static bool selftest_opcodes_all(void)

{

	bool pass = true;

	unsigned int i;



	for (i = 0; i < ARRAY_SIZE(selftest_opcodes); ++i)

		pass = pass && selftest_opcode_one(&selftest_opcodes[i]);



	return pass;

}



bool kmemcheck_selftest(void)

{

	bool pass = true;



	pass = pass && selftest_opcodes_all();



	return pass;

}

arch/x86/mm/kmemcheck/selftest.h

0 → 100644
+6 −0
Original line number Diff line number Diff line 
#ifndef ARCH_X86_MM_KMEMCHECK_SELFTEST_H

#define ARCH_X86_MM_KMEMCHECK_SELFTEST_H



bool kmemcheck_selftest(void);



#endif