This is a note to let you know that I've just added the patch titled KVM: s390: fix guarded storage control register handling to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-s390-fix-guarded-storage-control-register-handling.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 44bada28219031f9e8e86b84460606efa57b871e Mon Sep 17 00:00:00 2001 From: Heiko Carstens <hca@xxxxxxxxxxxxx> Date: Thu, 15 Apr 2021 10:01:27 +0200 Subject: KVM: s390: fix guarded storage control register handling From: Heiko Carstens <hca@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx> Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 4.12 Link: https://lore.kernel.org/r/20210415080127.1061275-1-hca@xxxxxxxxxxxxx Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -3624,16 +3624,16 @@ 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(); } /* SIE will save etoken directly into SDNX and therefore kvm_run */ } Patches currently in stable-queue which might be from hca@xxxxxxxxxxxxx are queue-4.19/s390-archrandom-add-parameter-check-for-s390_arch_ra.patch queue-4.19/s390-disassembler-increase-ebpf-disasm-buffer-size.patch queue-4.19/kvm-s390-fix-guarded-storage-control-register-handling.patch