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 <hpa@linux.intel.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/arch/powerpc/include/asm/archrandom.h b/arch/powerpc/include/asm/archrandom.h
index d853d163ba4730ddac3eff5793f5f4fe8861a330..801beba4e64b2de80e741d879e1991504a016858 100644 (file)
--- a/arch/powerpc/include/asm/archrandom.h
+++ b/arch/powerpc/include/asm/archrandom.h
@@ -27,6 +27,15 @@ static inline int arch_get_random_int(unsigned int *v)
 
 int powernv_get_random_long(unsigned long *v);
 
+static inline int arch_get_random_seed_long(unsigned long *v)
+{
+       return 0;
+}
+static inline int arch_get_random_seed_int(unsigned int *v)
+{
+       return 0;
+}
+
 #endif /* CONFIG_ARCH_RANDOM */
 
 #endif /* _ASM_POWERPC_ARCHRANDOM_H */

diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index e6a92455740e6a5dfc64c5b1a1193a693594feab..6ad7f6d3f97f4824d5cdaf7b0107e1c65d4047eb 100644 (file)
--- 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 <fenghua.yu@intel.com>,
  *          H. Peter Anvin <hpa@linux.intel.com>
  *
@@ -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);

diff --git a/include/linux/random.h b/include/linux/random.h
index 1cfce0e24dbdb09a527d914ab511e6b6280fa364..c2f08131050d5facd1a5a60493911e474983c103 100644 (file)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -88,6 +88,14 @@ static inline int arch_get_random_int(unsigned int *v)
 {
        return 0;
 }
+static inline int arch_get_random_seed_long(unsigned long *v)
+{
+       return 0;
+}
+static inline int arch_get_random_seed_int(unsigned int *v)
+{
+       return 0;
+}
 #endif
 
 /* Pseudo random number generator from numerical recipes. */