The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7c83d096aed055a7763a03384f92115363448b71 Mon Sep 17 00:00:00 2001

From: Sean Christopherson sean.j.christopherson@intel.com Date: Thu, 2 Jul 2020 21:04:21 -0700 Subject: [PATCH] KVM: x86: Mark CR4.TSD as being possibly owned by the guest

Mark CR4.TSD as being possibly owned by the guest as that is indeed the case on VMX. Without TSD being tagged as possibly owned by the guest, a targeted read of CR4 to get TSD could observe a stale value. This bug is benign in the current code base as the sole consumer of TSD is the emulator (for RDTSC) and the emulator always "reads" the entirety of CR4 when grabbing bits.

Add a build-time assertion in to ensure VMX doesn't hand over more CR4 bits without also updating x86.

Fixes: 52ce3c21aec3 ("x86,kvm,vmx: Don't trap writes to CR4.TSD") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com Message-Id: 20200703040422.31536-2-sean.j.christopherson@intel.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com

diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h index ff2d0e9ca3bc..cfe83d4ae625 100644 --- a/arch/x86/kvm/kvm_cache_regs.h +++ b/arch/x86/kvm/kvm_cache_regs.h @@ -7,7 +7,7 @@ #define KVM_POSSIBLE_CR0_GUEST_BITS X86_CR0_TS #define KVM_POSSIBLE_CR4_GUEST_BITS \ (X86_CR4_PVI | X86_CR4_DE | X86_CR4_PCE | X86_CR4_OSFXSR \ - | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_PGE) + | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_PGE | X86_CR4_TSD)

#define BUILD_KVM_GPR_ACCESSORS(lname, uname) \ static __always_inline unsigned long kvm_##lname##_read(struct kvm_vcpu *vcpu)\ diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index cb22f33bf1d8..5c9bfc0b9ab9 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -4034,6 +4034,8 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)

void set_cr4_guest_host_mask(struct vcpu_vmx *vmx) { + BUILD_BUG_ON(KVM_CR4_GUEST_OWNED_BITS & ~KVM_POSSIBLE_CR4_GUEST_BITS); + vmx->vcpu.arch.cr4_guest_owned_bits = KVM_CR4_GUEST_OWNED_BITS; if (enable_ept) vmx->vcpu.arch.cr4_guest_owned_bits |= X86_CR4_PGE;