diff options
Diffstat (limited to 'arch/x86/kernel/cpu/rdrand.c')
| -rw-r--r-- | arch/x86/kernel/cpu/rdrand.c | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c index 5c900f9527ff..c4be62058dd9 100644 --- a/arch/x86/kernel/cpu/rdrand.c +++ b/arch/x86/kernel/cpu/rdrand.c @@ -29,7 +29,8 @@ __setup("nordrand", x86_rdrand_setup); #ifdef CONFIG_ARCH_RANDOM void x86_init_rdrand(struct cpuinfo_x86 *c) { - unsigned long tmp; + unsigned int changed = 0; + unsigned long tmp, prev; int i; if (!cpu_has(c, X86_FEATURE_RDRAND)) @@ -42,5 +43,24 @@ void x86_init_rdrand(struct cpuinfo_x86 *c) return; } } + + /* + * Stupid sanity-check whether RDRAND does *actually* generate + * some at least random-looking data. + */ + prev = tmp; + for (i = 0; i < SANITY_CHECK_LOOPS; i++) { + if (rdrand_long(&tmp)) { + if (prev != tmp) + changed++; + + prev = tmp; + } + } + + if (WARN_ON_ONCE(!changed)) + pr_emerg( +"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\""); + } #endif |