From: Heiko Carstens hca@linux.ibm.com
commit 44bada28219031f9e8e86b84460606efa57b871e upstream.
store_regs_fmt2() has an ordering problem: first the guarded storage facility is enabled on the local cpu, then preemption disabled, and then the STGSC (store guarded storage controls) instruction is executed.
If the process gets scheduled away between enabling the guarded storage facility and before preemption is disabled, this might lead to a special operation exception and therefore kernel crash as soon as the process is scheduled back and the STGSC instruction is executed.
Fixes: 4e0b1ab72b8a ("KVM: s390: gs support for kvm guests") Signed-off-by: Heiko Carstens hca@linux.ibm.com Reviewed-by: Christian Borntraeger borntraeger@de.ibm.com Reviewed-by: David Hildenbrand david@redhat.com Reviewed-by: Janosch Frank frankja@linux.ibm.com Reviewed-by: Cornelia Huck cohuck@redhat.com Cc: stable@vger.kernel.org # 4.12 Link: https://lore.kernel.org/r/20210415080127.1061275-1-hca@linux.ibm.com Signed-off-by: Christian Borntraeger borntraeger@de.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/s390/kvm/kvm-s390.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -3395,16 +3395,16 @@ static void store_regs(struct kvm_vcpu * current->thread.fpu.fpc = vcpu->arch.host_fpregs.fpc; current->thread.fpu.regs = vcpu->arch.host_fpregs.regs; if (MACHINE_HAS_GS) { + preempt_disable(); __ctl_set_bit(2, 4); if (vcpu->arch.gs_enabled) save_gs_cb(current->thread.gs_cb); - preempt_disable(); current->thread.gs_cb = vcpu->arch.host_gscb; restore_gs_cb(vcpu->arch.host_gscb); - preempt_enable(); if (!vcpu->arch.host_gscb) __ctl_clear_bit(2, 4); vcpu->arch.host_gscb = NULL; + preempt_enable(); }
}