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@xxxxxxxxxx>
---
arch/x86/kvm/vmx/nested.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 1c243758dd2c..c3624109ffeb 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5540,7 +5540,7 @@ 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) {
--
2.32.0.rc1.229.g3e70b5a671-goog
