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Message-Id: <a388d4536ecf5427237482bf8f9003de40bbc7e9.1407994704.git.luto@amacapital.net> Date: Wed, 13 Aug 2014 22:44:01 -0700 From: Andy Lutomirski <luto@...capital.net> To: kvm@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>, Theodore Ts'o <tytso@....edu>, linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>, x86@...nel.org Cc: Daniel Borkmann <dborkman@...hat.com>, Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>, Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>, Gleb Natapov <gleb@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Andrew Honig <ahonig@...gle.com>, Andy Lutomirski <luto@...capital.net> Subject: [PATCH v6 6/7] x86,random,kvm: Use KVM_GET_RNG_SEED in arch_rng_init This is a straightforward implementation: for each bit of internal RNG state, request one bit from KVM_GET_RNG_SEED. This is done even if RDSEED/RDRAND worked, since KVM_GET_RNG_SEED is likely to provide cryptographically secure output even if the CPU's RNG is weak or compromised. Acked-by: Paolo Bonzini <pbonzini@...hat.com> Signed-off-by: Andy Lutomirski <luto@...capital.net> --- arch/x86/Kconfig | 4 ++++ arch/x86/include/asm/kvm_guest.h | 9 +++++++++ arch/x86/kernel/archrandom.c | 25 ++++++++++++++++++++++++- arch/x86/kernel/kvm.c | 10 ++++++++++ 4 files changed, 47 insertions(+), 1 deletion(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index d24887b..ad87278 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -594,6 +594,7 @@ config KVM_GUEST bool "KVM Guest support (including kvmclock)" depends on PARAVIRT select PARAVIRT_CLOCK + select ARCH_RANDOM default y ---help--- This option enables various optimizations for running under the KVM @@ -1508,6 +1509,9 @@ config ARCH_RANDOM If supported, this is a high bandwidth, cryptographically secure hardware random number generator. + This also enables paravirt RNGs such as KVM's if the relevant + PV guest support is enabled. + config X86_SMAP def_bool y prompt "Supervisor Mode Access Prevention" if EXPERT diff --git a/arch/x86/include/asm/kvm_guest.h b/arch/x86/include/asm/kvm_guest.h index a92b176..8c4dbd5 100644 --- a/arch/x86/include/asm/kvm_guest.h +++ b/arch/x86/include/asm/kvm_guest.h @@ -3,4 +3,13 @@ int kvm_setup_vsyscall_timeinfo(void); +#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_ARCH_RANDOM) +extern bool kvm_get_rng_seed(u64 *rv); +#else +static inline bool kvm_get_rng_seed(u64 *rv) +{ + return false; +} +#endif + #endif /* _ASM_X86_KVM_GUEST_H */ diff --git a/arch/x86/kernel/archrandom.c b/arch/x86/kernel/archrandom.c index e8d2ffb..adbaa25 100644 --- a/arch/x86/kernel/archrandom.c +++ b/arch/x86/kernel/archrandom.c @@ -15,6 +15,7 @@ */ #include <asm/archrandom.h> +#include <asm/kvm_guest.h> void arch_rng_init(void *ctx, void (*seed)(void *ctx, u32 data), @@ -22,7 +23,7 @@ void arch_rng_init(void *ctx, const char *log_prefix) { int i; - int rdseed_bits = 0, rdrand_bits = 0; + int rdseed_bits = 0, rdrand_bits = 0, kvm_bits = 0; char buf[128] = ""; char *msgptr = buf; @@ -42,10 +43,32 @@ void arch_rng_init(void *ctx, #endif } + /* + * Use KVM_GET_RNG_SEED regardless of whether the CPU RNG + * worked, since it incorporates entropy unavailable to the CPU, + * and we shouldn't trust the hardware RNG more than we need to. + * We request enough bits for the entire internal RNG state, + * because there's no good reason not to. + */ + for (i = 0; i < bits_per_source; i += 64) { + u64 rv; + + if (kvm_get_rng_seed(&rv)) { + seed(ctx, (u32)rv); + seed(ctx, (u32)(rv >> 32)); + kvm_bits += 8 * sizeof(rv); + } else { + break; /* If it fails once, it will keep failing. */ + } + } + if (rdseed_bits) msgptr += sprintf(msgptr, ", %d bits from RDSEED", rdseed_bits); if (rdrand_bits) msgptr += sprintf(msgptr, ", %d bits from RDRAND", rdrand_bits); + if (kvm_bits) + msgptr += sprintf(msgptr, ", %d bits from KVM_GET_RNG_BITS", + kvm_bits); if (buf[0]) pr_info("%s with %s\n", log_prefix, buf + 2); } diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 3dd8e2c..bd8783a 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -416,6 +416,16 @@ void kvm_disable_steal_time(void) wrmsr(MSR_KVM_STEAL_TIME, 0, 0); } +bool kvm_get_rng_seed(u64 *v) +{ + /* + * Allow migration from a hypervisor with the GET_RNG_SEED + * feature to a hypervisor without it. + */ + return (kvm_para_has_feature(KVM_FEATURE_GET_RNG_SEED) && + rdmsrl_safe(MSR_KVM_GET_RNG_SEED, v) == 0); +} + #ifdef CONFIG_SMP static void __init kvm_smp_prepare_boot_cpu(void) { -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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