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Message-Id: <d6fb35de2ccd90532f62d58016428fc91ca2dd8d.1407994704.git.luto@amacapital.net> Date: Wed, 13 Aug 2014 22:43:58 -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 4/7] x86,kvm: Add MSR_KVM_GET_RNG_SEED and a matching feature bit This adds a simple interface to allow a guest to request 64 bits of host nonblocking entropy. This is independent of virtio-rng for a couple of reasons: - It's intended to be usable during early boot, when a trivial synchronous interface is needed. - virtio-rng gives blocking entropy, and making guest boot wait for the host's /dev/random will cause problems. MSR_KVM_GET_RNG_SEED is intended to provide 64 bits of best-effort cryptographically secure data for use as a seed. It provides no guarantee that the result contains any actual entropy. Acked-by: Paolo Bonzini <pbonzini@...hat.com> Signed-off-by: Andy Lutomirski <luto@...capital.net> --- Documentation/virtual/kvm/cpuid.txt | 3 +++ arch/x86/include/uapi/asm/kvm_para.h | 2 ++ arch/x86/kvm/cpuid.c | 3 ++- arch/x86/kvm/x86.c | 4 ++++ 4 files changed, 11 insertions(+), 1 deletion(-) diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 3c65feb..0ab043b 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -54,6 +54,9 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit || || before enabling paravirtualized || || spinlock support. ------------------------------------------------------------------------------ +KVM_FEATURE_GET_RNG_SEED || 8 || host provides rng seed data via + || || MSR_KVM_GET_RNG_SEED. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index 94dc8ca..e2eaf93 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -24,6 +24,7 @@ #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 #define KVM_FEATURE_PV_UNHALT 7 +#define KVM_FEATURE_GET_RNG_SEED 8 /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored. @@ -40,6 +41,7 @@ #define MSR_KVM_ASYNC_PF_EN 0x4b564d02 #define MSR_KVM_STEAL_TIME 0x4b564d03 #define MSR_KVM_PV_EOI_EN 0x4b564d04 +#define MSR_KVM_GET_RNG_SEED 0x4b564d05 struct kvm_steal_time { __u64 steal; diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 38a0afe..40d6763 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -479,7 +479,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, (1 << KVM_FEATURE_ASYNC_PF) | (1 << KVM_FEATURE_PV_EOI) | (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) | - (1 << KVM_FEATURE_PV_UNHALT); + (1 << KVM_FEATURE_PV_UNHALT) | + (1 << KVM_FEATURE_GET_RNG_SEED); if (sched_info_on()) entry->eax |= (1 << KVM_FEATURE_STEAL_TIME); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ef432f8..695b682 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -48,6 +48,7 @@ #include <linux/pci.h> #include <linux/timekeeper_internal.h> #include <linux/pvclock_gtod.h> +#include <linux/random.h> #include <trace/events/kvm.h> #define CREATE_TRACE_POINTS @@ -2480,6 +2481,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata) case MSR_KVM_PV_EOI_EN: data = vcpu->arch.pv_eoi.msr_val; break; + case MSR_KVM_GET_RNG_SEED: + get_random_bytes(&data, sizeof(data)); + break; case MSR_IA32_P5_MC_ADDR: case MSR_IA32_P5_MC_TYPE: case MSR_IA32_MCG_CAP: -- 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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