From c4d2188206bafa177ea58e9a25b952baa0bf7712 Mon Sep 17 00:00:00 2001 From: Wei Huang Date: Tue, 1 May 2018 09:49:54 -0500 Subject: [PATCH] KVM: x86: Update cpuid properly when CR4.OSXAVE or CR4.PKE is changed MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The CPUID bits of OSXSAVE (function=0x1) and OSPKE (func=0x7, leaf=0x0) allows user apps to detect if OS has set CR4.OSXSAVE or CR4.PKE. KVM is supposed to update these CPUID bits when CR4 is updated. Current KVM code doesn't handle some special cases when updates come from emulator. Here is one example: Step 1: guest boots Step 2: guest OS enables XSAVE ==> CR4.OSXSAVE=1 and CPUID.OSXSAVE=1 Step 3: guest hot reboot ==> QEMU reset CR4 to 0, but CPUID.OSXAVE==1 Step 4: guest os checks CPUID.OSXAVE, detects 1, then executes xgetbv Step 4 above will cause an #UD and guest crash because guest OS hasn't turned on OSXAVE yet. This patch solves the problem by comparing the the old_cr4 with cr4. If the related bits have been changed, kvm_update_cpuid() needs to be called. Signed-off-by: Wei Huang Reviewed-by: Bandan Das Cc: stable@vger.kernel.org Signed-off-by: Radim Krčmář --- arch/x86/kvm/x86.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 59371de5d722..e3103279eadd 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7985,6 +7985,7 @@ static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs) { struct msr_data apic_base_msr; int mmu_reset_needed = 0; + int cpuid_update_needed = 0; int pending_vec, max_bits, idx; struct desc_ptr dt; int ret = -EINVAL; @@ -8023,8 +8024,10 @@ static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs) vcpu->arch.cr0 = sregs->cr0; mmu_reset_needed |= kvm_read_cr4(vcpu) != sregs->cr4; + cpuid_update_needed |= ((kvm_read_cr4(vcpu) ^ sregs->cr4) & + (X86_CR4_OSXSAVE | X86_CR4_PKE)); kvm_x86_ops->set_cr4(vcpu, sregs->cr4); - if (sregs->cr4 & (X86_CR4_OSXSAVE | X86_CR4_PKE)) + if (cpuid_update_needed) kvm_update_cpuid(vcpu); idx = srcu_read_lock(&vcpu->kvm->srcu); -- 2.30.2