• Haozhong Zhang's avatar
    KVM: nVMX: fix guest CR4 loading when emulating L2 to L1 exit · 8eb3f87d
    Haozhong Zhang authored
    When KVM emulates an exit from L2 to L1, it loads L1 CR4 into the
    guest CR4. Before this CR4 loading, the guest CR4 refers to L2
    CR4. Because these two CR4's are in different levels of guest, we
    should vmx_set_cr4() rather than kvm_set_cr4() here. The latter, which
    is used to handle guest writes to its CR4, checks the guest change to
    CR4 and may fail if the change is invalid.
    
    The failure may cause trouble. Consider we start
      a L1 guest with non-zero L1 PCID in use,
         (i.e. L1 CR4.PCIDE == 1 && L1 CR3.PCID != 0)
    and
      a L2 guest with L2 PCID disabled,
         (i.e. L2 CR4.PCIDE == 0)
    and following events may happen:
    
    1. If kvm_set_cr4() is used in load_vmcs12_host_state() to load L1 CR4
       into guest CR4 (in VMCS01) for L2 to L1 exit, it will fail because
       of PCID check. As a result, the guest CR4 recorded in L0 KVM (i.e.
       vcpu->arch.cr4) is left to the value of L2 CR4.
    
    2. Later, if L1 attempts to change its CR4, e.g., clearing VMXE bit,
       kvm_set_cr4() in L0 KVM will think L1 also wants to enable PCID,
       because the wrong L2 CR4 is used by L0 KVM as L1 CR4. As L1
       CR3.PCID != 0, L0 KVM will inject GP to L1 guest.
    
    Fixes: 4704d0be ("KVM: nVMX: Exiting from L2 to L1")
    Cc: qemu-stable@nongnu.org
    Signed-off-by: default avatarHaozhong Zhang <haozhong.zhang@intel.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    8eb3f87d
vmx.c 343 KB