diff options
Diffstat (limited to '')
| -rw-r--r-- | arch/x86/kernel/cpu/rdrand.c | 59 |
1 files changed, 21 insertions, 38 deletions
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c index c4be62058dd9..26a427fa84ea 100644 --- a/arch/x86/kernel/cpu/rdrand.c +++ b/arch/x86/kernel/cpu/rdrand.c @@ -11,56 +11,39 @@ #include <asm/archrandom.h> #include <asm/sections.h> -static int __init x86_rdrand_setup(char *s) -{ - setup_clear_cpu_cap(X86_FEATURE_RDRAND); - setup_clear_cpu_cap(X86_FEATURE_RDSEED); - return 1; -} -__setup("nordrand", x86_rdrand_setup); - /* * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation. - * Run the instruction a few times as a sanity check. - * If it fails, it is simple to disable RDRAND here. + * Run the instruction a few times as a sanity check. Also make sure + * it's not outputting the same value over and over, which has happened + * as a result of past CPU bugs. + * + * If it fails, it is simple to disable RDRAND and RDSEED here. */ -#define SANITY_CHECK_LOOPS 8 -#ifdef CONFIG_ARCH_RANDOM void x86_init_rdrand(struct cpuinfo_x86 *c) { - unsigned int changed = 0; - unsigned long tmp, prev; - int i; + enum { SAMPLES = 8, MIN_CHANGE = 5 }; + unsigned long sample, prev; + bool failure = false; + size_t i, changed; if (!cpu_has(c, X86_FEATURE_RDRAND)) return; - for (i = 0; i < SANITY_CHECK_LOOPS; i++) { - if (!rdrand_long(&tmp)) { - clear_cpu_cap(c, X86_FEATURE_RDRAND); - pr_warn_once("rdrand: disabled\n"); - return; + for (changed = 0, i = 0; i < SAMPLES; ++i) { + if (!rdrand_long(&sample)) { + failure = true; + break; } + changed += i && sample != prev; + prev = sample; } + if (changed < MIN_CHANGE) + failure = true; - /* - * 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 (failure) { + clear_cpu_cap(c, X86_FEATURE_RDRAND); + clear_cpu_cap(c, X86_FEATURE_RDSEED); + pr_emerg("RDRAND is not reliable on this platform; disabling.\n"); } - - if (WARN_ON_ONCE(!changed)) - pr_emerg( -"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\""); - } -#endif |