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x86, kaslr: Provide randomness functions

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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: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/1381450698-28710-4-git-send-email-keescook@chromium.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Kees Cook 2013-10-10 17:18:15 -07:00 committed by H. Peter Anvin
parent 8ab3820fd5
commit 5bfce5ef55
4 changed files with 76 additions and 14 deletions
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53
arch/x86/boot/compressed/aslr.c
View File

@ -1,6 +1,59 @@
#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,

2
arch/x86/boot/compressed/misc.h
View File

@ -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,

21
arch/x86/include/asm/archrandom.h
View File

@ -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);

14
arch/x86/kernel/cpu/rdrand.c
View File

@ -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