| Message ID | 20220917000928.118-1-justinien.bouron@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Handle MXCSR in kvm_arch_vcpu_ioctl_{get,set}_fpu. | expand |
On Sat, Sep 17, 2022, Justinien Bouron wrote: > kvm_arch_vcpu_ioctl_get_fpu does not set the mxcsr in the kvm_fpu > struct; conversely kvm_arch_vcpu_ioctl_set_fpu does not set the mxcsr > value in the fxregs_state struct of the vcpu. > This leads to the KVM_GET_FPU ioctl returning 0 as the mxcsr value, > regardless of the actual value on the vcpu; while KVM_SET_FPU leaves the > MXCSR on the vcpu untouched. > > Fix kvm_arch_vcpu_ioctl_{get,set}_fpu to properly handle MXCSR. > > Signed-off-by: Justinien Bouron <justinien.bouron@gmail.com> > --- > arch/x86/kvm/x86.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 43a6a7efc6ec..c33a2599a497 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -11462,6 +11462,7 @@ int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu) > fpu->last_ip = fxsave->rip; > fpu->last_dp = fxsave->rdp; > memcpy(fpu->xmm, fxsave->xmm_space, sizeof(fxsave->xmm_space)); > + fpu->mxcsr = fxsave->mxcsr; > > vcpu_put(vcpu); > return 0; > @@ -11486,6 +11487,7 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu) > fxsave->rip = fpu->last_ip; > fxsave->rdp = fpu->last_dp; > memcpy(fxsave->xmm_space, fpu->xmm, sizeof(fxsave->xmm_space)); > + fxsave->mxcsr = fpu->mxcsr; The incoming MXCSR needs to be vetted, e.g. see fpu_copy_uabi_to_guest_fpstate(). That said, this code is incredibly ancient and has been obsolete for years. I wonder if we can get away with deprecating KVM_{G,S}ET_FPU on x86 and leaving the broken behavior as-is.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 43a6a7efc6ec..c33a2599a497 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11462,6 +11462,7 @@ int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu) fpu->last_ip = fxsave->rip; fpu->last_dp = fxsave->rdp; memcpy(fpu->xmm, fxsave->xmm_space, sizeof(fxsave->xmm_space)); + fpu->mxcsr = fxsave->mxcsr; vcpu_put(vcpu); return 0; @@ -11486,6 +11487,7 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu) fxsave->rip = fpu->last_ip; fxsave->rdp = fpu->last_dp; memcpy(fxsave->xmm_space, fpu->xmm, sizeof(fxsave->xmm_space)); + fxsave->mxcsr = fpu->mxcsr; vcpu_put(vcpu); return 0;
kvm_arch_vcpu_ioctl_get_fpu does not set the mxcsr in the kvm_fpu struct; conversely kvm_arch_vcpu_ioctl_set_fpu does not set the mxcsr value in the fxregs_state struct of the vcpu. This leads to the KVM_GET_FPU ioctl returning 0 as the mxcsr value, regardless of the actual value on the vcpu; while KVM_SET_FPU leaves the MXCSR on the vcpu untouched. Fix kvm_arch_vcpu_ioctl_{get,set}_fpu to properly handle MXCSR. Signed-off-by: Justinien Bouron <justinien.bouron@gmail.com> --- arch/x86/kvm/x86.c | 2 ++ 1 file changed, 2 insertions(+)