x86/kvm: move kvm_load/put_guest_xcr0 into atomic context

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guest xcr0 could leak into host when MCE happens in guest mode. Because
do_machine_check() could schedule out at a few places.

For example:

kvm_load_guest_xcr0
...
kvm_x86_ops->run(vcpu) {
  vmx_vcpu_run
    vmx_complete_atomic_exit
      kvm_machine_check
        do_machine_check
          do_memory_failure
            memory_failure
              lock_page

In this case, host_xcr0 is 0x2ff, guest vcpu xcr0 is 0xff. After schedule
out, host cpu has guest xcr0 loaded (0xff).

In __switch_to {
     switch_fpu_finish
       copy_kernel_to_fpregs
         XRSTORS

If any bit i in XSTATE_BV[i] == 1 and xcr0[i] == 0, XRSTORS will
generate #GP (In this case, bit 9). Then ex_handler_fprestore kicks in
and tries to reinitialize fpu by restoring init fpu state. Same story as
last #GP, except we get DOUBLE FAULT this time.

Cc: stable@vger.kernel.org
Signed-off-by: WANG Chao <chao.wang@ucloud.cn>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

...

This commit is contained in:

WANG Chao 2019-04-12 15:55:39 +08:00 • committed by Paolo Bonzini

parent 99c221796a

commit 1811d979c7

4 changed files with 12 additions and 6 deletions

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2

arch/x86/kvm/svm.c

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4

arch/x86/kvm/vmx/vmx.c

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10

arch/x86/kvm/x86.c

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2

arch/x86/kvm/x86.h

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