From d20f78d252778e0fae8f8256e602bd682eb2185c Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Mon, 17 Mar 2014 16:36:27 -0700 Subject: x86, random: Enable the RDSEED instruction Upcoming Intel silicon adds a new RDSEED instruction, which is similar to RDRAND but provides a stronger guarantee: unlike RDRAND, RDSEED will always reseed the PRNG from the true random number source between each read. Thus, the output of RDSEED is guaranteed to be 100% entropic, unlike RDRAND which is only architecturally guaranteed to be 1/512 entropic (although in practice is much more.) The RDSEED instruction takes the same time to execute as RDRAND, but RDSEED unlike RDRAND can legitimately return failure (CF=0) due to entropy exhaustion if too many threads on too many cores are hammering the RDSEED instruction at the same time. Therefore, we have to be more conservative and only use it in places where we can tolerate failures. This patch introduces the primitives arch_get_random_seed_{int,long}() but does not use it yet. Signed-off-by: H. Peter Anvin Reviewed-by: Ingo Molnar Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Signed-off-by: Theodore Ts'o --- arch/x86/include/asm/archrandom.h | 39 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h index e6a9245..6ad7f6d 100644 --- a/arch/x86/include/asm/archrandom.h +++ b/arch/x86/include/asm/archrandom.h @@ -1,7 +1,7 @@ /* * This file is part of the Linux kernel. * - * Copyright (c) 2011, Intel Corporation + * Copyright (c) 2011-2014, Intel Corporation * Authors: Fenghua Yu , * H. Peter Anvin * @@ -31,10 +31,13 @@ #define RDRAND_RETRY_LOOPS 10 #define RDRAND_INT ".byte 0x0f,0xc7,0xf0" +#define RDSEED_INT ".byte 0x0f,0xc7,0xf8" #ifdef CONFIG_X86_64 # define RDRAND_LONG ".byte 0x48,0x0f,0xc7,0xf0" +# define RDSEED_LONG ".byte 0x48,0x0f,0xc7,0xf8" #else # define RDRAND_LONG RDRAND_INT +# define RDSEED_LONG RDSEED_INT #endif #ifdef CONFIG_ARCH_RANDOM @@ -53,6 +56,16 @@ static inline int rdrand_long(unsigned long *v) return ok; } +/* A single attempt at RDSEED */ +static inline bool rdseed_long(unsigned long *v) +{ + unsigned char ok; + asm volatile(RDSEED_LONG "\n\t" + "setc %0" + : "=qm" (ok), "=a" (*v)); + return ok; +} + #define GET_RANDOM(name, type, rdrand, nop) \ static inline int name(type *v) \ { \ @@ -70,16 +83,35 @@ static inline int name(type *v) \ return ok; \ } +#define GET_SEED(name, type, rdseed, nop) \ +static inline int name(type *v) \ +{ \ + unsigned char ok; \ + alternative_io("movb $0, %0\n\t" \ + nop, \ + rdseed "\n\t" \ + "setc %0", \ + X86_FEATURE_RDSEED, \ + ASM_OUTPUT2("=q" (ok), "=a" (*v))); \ + return ok; \ +} + #ifdef CONFIG_X86_64 GET_RANDOM(arch_get_random_long, unsigned long, RDRAND_LONG, ASM_NOP5); GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP4); +GET_SEED(arch_get_random_seed_long, unsigned long, RDSEED_LONG, ASM_NOP5); +GET_SEED(arch_get_random_seed_int, unsigned int, RDSEED_INT, ASM_NOP4); + #else GET_RANDOM(arch_get_random_long, unsigned long, RDRAND_LONG, ASM_NOP3); GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP3); +GET_SEED(arch_get_random_seed_long, unsigned long, RDSEED_LONG, ASM_NOP4); +GET_SEED(arch_get_random_seed_int, unsigned int, RDSEED_INT, ASM_NOP4); + #endif /* CONFIG_X86_64 */ #else @@ -89,6 +121,11 @@ static inline int rdrand_long(unsigned long *v) return 0; } +static inline bool rdseed_long(unsigned long *v) +{ + return 0; +} + #endif /* CONFIG_ARCH_RANDOM */ extern void x86_init_rdrand(struct cpuinfo_x86 *c); -- cgit v1.1 From 7b878d4b48c4e04b936918bb83836a107ba453b3 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Mon, 17 Mar 2014 16:36:30 -0700 Subject: random: Add arch_has_random[_seed]() Add predicate functions for having arch_get_random[_seed]*(). The only current use is to avoid the loop in arch_random_refill() when arch_get_random_seed_long() is unavailable. Signed-off-by: H. Peter Anvin Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Signed-off-by: Theodore Ts'o --- arch/x86/include/asm/archrandom.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h index 6ad7f6d..69f1366 100644 --- a/arch/x86/include/asm/archrandom.h +++ b/arch/x86/include/asm/archrandom.h @@ -114,6 +114,9 @@ GET_SEED(arch_get_random_seed_int, unsigned int, RDSEED_INT, ASM_NOP4); #endif /* CONFIG_X86_64 */ +#define arch_has_random() static_cpu_has(X86_FEATURE_RDRAND) +#define arch_has_random_seed() static_cpu_has(X86_FEATURE_RDSEED) + #else static inline int rdrand_long(unsigned long *v) -- cgit v1.1