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>

1 files changed, 21 insertions, 0 deletions

diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index 0d9ec770f2f8..e6a92455740e 100644
--- a/arch/x86/include/asm/archrandom.h
+++ b/arch/x86/include/asm/archrandom.h
@@ -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);