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Commit 5bfce5ef authored by Kees Cook's avatar Kees Cook Committed by H. Peter Anvin
Browse files

x86, kaslr: Provide randomness functions 



Adds potential sources of randomness: RDRAND, RDTSC, or the i8254.

This moves the pre-alternatives inline rdrand function into the header so
both pieces of code can use it. Availability of RDRAND is then controlled
by CONFIG_ARCH_RANDOM, if someone wants to disable it even for kASLR.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/1381450698-28710-4-git-send-email-keescook@chromium.org


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 8ab3820f

arch/x86/boot/compressed/aslr.c

+53 −0
Original line number Diff line number Diff line 
#include "misc.h"



#ifdef CONFIG_RANDOMIZE_BASE

#include <asm/msr.h>

#include <asm/archrandom.h>



#define I8254_PORT_CONTROL	0x43

#define I8254_PORT_COUNTER0	0x40

#define I8254_CMD_READBACK	0xC0

#define I8254_SELECT_COUNTER0	0x02

#define I8254_STATUS_NOTREADY	0x40

static inline u16 i8254(void)

{

	u16 status, timer;



	do {

		outb(I8254_PORT_CONTROL,

		     I8254_CMD_READBACK | I8254_SELECT_COUNTER0);

		status = inb(I8254_PORT_COUNTER0);

		timer  = inb(I8254_PORT_COUNTER0);

		timer |= inb(I8254_PORT_COUNTER0) << 8;

	} while (status & I8254_STATUS_NOTREADY);



	return timer;

}



static unsigned long get_random_long(void)

{

	unsigned long random;



	if (has_cpuflag(X86_FEATURE_RDRAND)) {

		debug_putstr("KASLR using RDRAND...\n");

		if (rdrand_long(&random))

			return random;

	}



	if (has_cpuflag(X86_FEATURE_TSC)) {

		uint32_t raw;



		debug_putstr("KASLR using RDTSC...\n");

		rdtscl(raw);



		/* Only use the low bits of rdtsc. */

		random = raw & 0xffff;

	} else {

		debug_putstr("KASLR using i8254...\n");

		random = i8254();

	}



	/* Extend timer bits poorly... */

	random |= (random << 16);

#ifdef CONFIG_X86_64

	random |= (random << 32);

#endif

	return random;

}



unsigned char *choose_kernel_location(unsigned char *input,

				      unsigned long input_size,

arch/x86/boot/compressed/misc.h

+2 −0
Original line number Diff line number Diff line
@@ -52,6 +52,8 @@ unsigned char *choose_kernel_location(unsigned char *input, 
				      unsigned long input_size,

				      unsigned char *output,

				      unsigned long output_size);

/* cpuflags.c */

bool has_cpuflag(int flag);

#else

static inline

unsigned char *choose_kernel_location(unsigned char *input,

arch/x86/include/asm/archrandom.h

+21 −0
Original line number Diff line number Diff line
@@ -39,6 +39,20 @@ 


#ifdef CONFIG_ARCH_RANDOM



/* Instead of arch_get_random_long() when alternatives haven't run. */

static inline int rdrand_long(unsigned long *v)

{

	int ok;

	asm volatile("1: " RDRAND_LONG "\n\t"

		     "jc 2f\n\t"

		     "decl %0\n\t"

		     "jnz 1b\n\t"

		     "2:"

		     : "=r" (ok), "=a" (*v)

		     : "0" (RDRAND_RETRY_LOOPS));

	return ok;

}



#define GET_RANDOM(name, type, rdrand, nop)			\

static inline int name(type *v)					\

{								\
@@ -68,6 +82,13 @@ GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP3); 


#endif /* CONFIG_X86_64 */



#else



static inline int rdrand_long(unsigned long *v)

{

	return 0;

}



#endif  /* CONFIG_ARCH_RANDOM */



extern void x86_init_rdrand(struct cpuinfo_x86 *c);

arch/x86/kernel/cpu/rdrand.c

+0 −14
Original line number Diff line number Diff line
@@ -31,20 +31,6 @@ static int __init x86_rdrand_setup(char *s) 
}

__setup("nordrand", x86_rdrand_setup);



/* We can't use arch_get_random_long() here since alternatives haven't run */

static inline int rdrand_long(unsigned long *v)

{

	int ok;

	asm volatile("1: " RDRAND_LONG "\n\t"

		     "jc 2f\n\t"

		     "decl %0\n\t"

		     "jnz 1b\n\t"

		     "2:"

		     : "=r" (ok), "=a" (*v)

		     : "0" (RDRAND_RETRY_LOOPS));

	return ok;

}



/*

 * Force a reseed cycle; we are architecturally guaranteed a reseed

 * after no more than 512 128-bit chunks of random data.  This also