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KVM: nVMX: Ensure 64-bit shift when checking VMFUNC bitmap

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Use BIT_ULL() instead of an open-coded shift to check whether or not a
function is enabled in L1's VMFUNC bitmap.  This is a benign bug as KVM
supports only bit 0, and will fail VM-Enter if any other bits are set,
i.e. bits 63:32 are guaranteed to be zero.

Note, "function" is bounded by hardware as VMFUNC will #UD before taking
a VM-Exit if the function is greater than 63.

Before:
  if ((vmcs12->vm_function_control & (1 << function)) == 0)
   0x000000000001a916 <+118>:	mov    $0x1,%eax
   0x000000000001a91b <+123>:	shl    %cl,%eax
   0x000000000001a91d <+125>:	cltq
   0x000000000001a91f <+127>:	and    0x128(%rbx),%rax

After:
  if (!(vmcs12->vm_function_control & BIT_ULL(function & 63)))
   0x000000000001a955 <+117>:	mov    0x128(%rbx),%rdx
   0x000000000001a95c <+124>:	bt     %rax,%rdx

Fixes: 27c42a1bb8 ("KVM: nVMX: Enable VMFUNC for the L1 hypervisor")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-06-09 16:42:22 -07:00 committed by Paolo Bonzini
parent 07ffaf343e
commit 0e75225dfa
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/vmx/nested.c
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@ -5598,7 +5598,7 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
}
vmcs12 = get_vmcs12(vcpu);
if ((vmcs12->vm_function_control & (1 << function)) == 0)
if (!(vmcs12->vm_function_control & BIT_ULL(function)))
goto fail;
switch (function) {