KVM: x86: Mark CR4.TSD as being possibly owned by the guest

commit 7c83d096aed055a7763a03384f92115363448b71 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/kvm_cache_regs.h b/arch/x86/kvm/kvm_cache_regs.h
index f500293dad8d6122704958be16bf343fe154ef15..ce4a9f1f845e5ccf54f55bcba190e0c108d536a1 100644 (file)
--- a/arch/x86/kvm/kvm_cache_regs.h
+++ b/arch/x86/kvm/kvm_cache_regs.h
@@ -5,7 +5,7 @@
 #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)
 
 static inline unsigned long kvm_register_read(struct kvm_vcpu *vcpu,
                                              enum kvm_reg reg)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 11e683ec6c8534239b48fe828cf662045c0b10eb..6876231778a9681cb2bb5f44988077889bf7a06b 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5592,6 +5592,8 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
 
 static 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;