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    KVM: x86: Fix potential put_fpu() w/o load_fpu() on MPX platform · f958bd23
    Sean Christopherson 提交于
    Unlike most state managed by XSAVE, MPX is initialized to zero on INIT.
    Because INITs are usually recognized in the context of a VCPU_RUN call,
    kvm_vcpu_reset() puts the guest's FPU so that the FPU state is resident
    in memory, zeros the MPX state, and reloads FPU state to hardware.  But,
    in the unlikely event that an INIT is recognized during
    kvm_arch_vcpu_ioctl_get_mpstate() via kvm_apic_accept_events(),
    kvm_vcpu_reset() will call kvm_put_guest_fpu() without a preceding
    kvm_load_guest_fpu() and corrupt the guest's FPU state (and possibly
    userspace's FPU state as well).
    
    Given that MPX is being removed from the kernel[*], fix the bug with the
    simple-but-ugly approach of loading the guest's FPU during
    KVM_GET_MP_STATE.
    
    [*] See commit f240652b ("x86/mpx: Remove MPX APIs").
    
    Fixes: f775b13e ("x86,kvm: move qemu/guest FPU switching out to vcpu_run")
    Cc: stable@vger.kernel.org
    Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
    Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
    f958bd23
x86.c 267.5 KB