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[02/15] KVM: nVMX: Ensure 64-bit shift when checking VMFUNC bitmap

Message ID 20210609234235.1244004-3-seanjc@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86/mmu: TLB fixes and related cleanups | expand

Commit Message

Sean Christopherson June 9, 2021, 11:42 p.m. UTC
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>
---
 arch/x86/kvm/vmx/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

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) {