Assert, via KVM_BUG_ON(), that guest FPU state isn't/is in use when
loading/putting the FPU to help detect KVM bugs without needing an assist
from KASAN. If an imbalanced load/put is detected, skip the redundant
load/put to avoid clobbering guest state and/or crashing the host.
Note, kvm_access_xstate_msr() already provides a similar assertion.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d1e048d14e88..67e5f735adf2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11807,6 +11807,9 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
/* Swap (qemu) user FPU context for the guest FPU context. */
static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
{
+ if (KVM_BUG_ON(vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm))
+ return;
+
/* Exclude PKRU, it's restored separately immediately after VM-Exit. */
fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, true);
trace_kvm_fpu(1);
@@ -11815,6 +11818,9 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
/* When vcpu_run ends, restore user space FPU context. */
static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
{
+ if (KVM_BUG_ON(!vcpu->arch.guest_fpu.fpstate->in_use, vcpu->kvm))
+ return;
+
fpu_swap_kvm_fpstate(&vcpu->arch.guest_fpu, false);
++vcpu->stat.fpu_reload;
trace_kvm_fpu(0);
--
2.51.1.930.gacf6e81ea2-goog