KVM: x86: Clear KVM's cached guest CR3 at RESET/INIT

commit 03a6e84069d1870f5b3d360e64cb330b66f76dee upstream.

Explicitly zero the guest's CR3 and mark it available+dirty at RESET/INIT.
Per Intel's SDM and AMD's APM, CR3 is zeroed at both RESET and INIT.  For
RESET, this is a nop as vcpu is zero-allocated.  For INIT, the bug has
likely escaped notice because no firmware/kernel puts its page tables root
at PA=0, let alone relies on INIT to get the desired CR3 for such page
tables.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210921000303.400537-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7ec7c2dce50652fc16a3f3fcca89431bb70d6391..09e01a76ab0df8accb33b8e1b80aef2141a113a0 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10873,6 +10873,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 
        static_call(kvm_x86_vcpu_reset)(vcpu, init_event);
 
+       vcpu->arch.cr3 = 0;
+       kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
+
        /*
         * Reset the MMU context if paging was enabled prior to INIT (which is
         * implied if CR0.PG=1 as CR0 will be '0' prior to RESET).  Unlike the