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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: 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>
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4 changed files with 76 additions and 14 deletions
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@ -1,6 +1,59 @@
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#include "misc.h"
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#ifdef CONFIG_RANDOMIZE_BASE
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#include <asm/msr.h>
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#include <asm/archrandom.h>
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#define I8254_PORT_CONTROL 0x43
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#define I8254_PORT_COUNTER0 0x40
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#define I8254_CMD_READBACK 0xC0
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#define I8254_SELECT_COUNTER0 0x02
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#define I8254_STATUS_NOTREADY 0x40
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static inline u16 i8254(void)
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{
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u16 status, timer;
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do {
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outb(I8254_PORT_CONTROL,
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I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
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status = inb(I8254_PORT_COUNTER0);
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timer = inb(I8254_PORT_COUNTER0);
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timer |= inb(I8254_PORT_COUNTER0) << 8;
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} while (status & I8254_STATUS_NOTREADY);
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return timer;
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}
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static unsigned long get_random_long(void)
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{
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unsigned long random;
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if (has_cpuflag(X86_FEATURE_RDRAND)) {
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debug_putstr("KASLR using RDRAND...\n");
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if (rdrand_long(&random))
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return random;
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}
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if (has_cpuflag(X86_FEATURE_TSC)) {
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uint32_t raw;
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debug_putstr("KASLR using RDTSC...\n");
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rdtscl(raw);
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/* Only use the low bits of rdtsc. */
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random = raw & 0xffff;
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} else {
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debug_putstr("KASLR using i8254...\n");
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random = i8254();
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}
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/* Extend timer bits poorly... */
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random |= (random << 16);
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#ifdef CONFIG_X86_64
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random |= (random << 32);
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#endif
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return random;
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}
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unsigned char *choose_kernel_location(unsigned char *input,
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unsigned long input_size,
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@ -52,6 +52,8 @@ unsigned char *choose_kernel_location(unsigned char *input,
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unsigned long input_size,
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unsigned char *output,
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unsigned long output_size);
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/* cpuflags.c */
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bool has_cpuflag(int flag);
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#else
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static inline
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unsigned char *choose_kernel_location(unsigned char *input,
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@ -39,6 +39,20 @@
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#ifdef CONFIG_ARCH_RANDOM
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/* Instead of arch_get_random_long() when alternatives haven't run. */
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static inline int rdrand_long(unsigned long *v)
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{
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int ok;
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asm volatile("1: " RDRAND_LONG "\n\t"
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"jc 2f\n\t"
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"decl %0\n\t"
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"jnz 1b\n\t"
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"2:"
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: "=r" (ok), "=a" (*v)
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: "0" (RDRAND_RETRY_LOOPS));
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return ok;
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}
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#define GET_RANDOM(name, type, rdrand, nop) \
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static inline int name(type *v) \
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{ \
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@ -68,6 +82,13 @@ GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP3);
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#endif /* CONFIG_X86_64 */
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#else
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static inline int rdrand_long(unsigned long *v)
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{
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return 0;
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}
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#endif /* CONFIG_ARCH_RANDOM */
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extern void x86_init_rdrand(struct cpuinfo_x86 *c);
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@ -31,20 +31,6 @@ static int __init x86_rdrand_setup(char *s)
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}
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__setup("nordrand", x86_rdrand_setup);
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/* We can't use arch_get_random_long() here since alternatives haven't run */
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static inline int rdrand_long(unsigned long *v)
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{
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int ok;
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asm volatile("1: " RDRAND_LONG "\n\t"
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"jc 2f\n\t"
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"decl %0\n\t"
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"jnz 1b\n\t"
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"2:"
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: "=r" (ok), "=a" (*v)
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: "0" (RDRAND_RETRY_LOOPS));
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return ok;
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}
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/*
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* Force a reseed cycle; we are architecturally guaranteed a reseed
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* after no more than 512 128-bit chunks of random data. This also
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