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

[ Upstream commit 0e75225dfa4c5d5d51291f54a3d2d5895bad38da ]

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: 27c42a1bb867 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index eca3db08d1831f313f7d8f0616076d4d6bf734dc..d3774d79916d668197bd04ef37b8df913c42cb09 100644 (file)
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5524,7 +5524,7 @@ 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) {