From 0e75225dfa4c5d5d51291f54a3d2d5895bad38da Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 9 Jun 2021 16:42:22 -0700 Subject: [PATCH] KVM: nVMX: Ensure 64-bit shift when checking VMFUNC bitmap 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 Message-Id: <20210609234235.1244004-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- 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 a9906c8344b8..775df9e2ff88 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -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) { -- GitLab