From: Thomas Huth thuth@redhat.com
commit 53936b5bf35e140ae27e4bbf0447a61063f400da upstream.
When the userspace program runs the KVM_S390_INTERRUPT ioctl to inject an interrupt, we convert them from the legacy struct kvm_s390_interrupt to the new struct kvm_s390_irq via the s390int_to_s390irq() function. However, this function does not take care of all types of interrupts that we can inject into the guest later (see do_inject_vcpu()). Since we do not clear out the s390irq values before calling s390int_to_s390irq(), there is a chance that we copy random data from the kernel stack which could be leaked to the userspace later.
Specifically, the problem exists with the KVM_S390_INT_PFAULT_INIT interrupt: s390int_to_s390irq() does not handle it, and the function __inject_pfault_init() later copies irq->u.ext which contains the random kernel stack data. This data can then be leaked either to the guest memory in __deliver_pfault_init(), or the userspace might retrieve it directly with the KVM_S390_GET_IRQ_STATE ioctl.
Fix it by handling that interrupt type in s390int_to_s390irq(), too, and by making sure that the s390irq struct is properly pre-initialized. And while we're at it, make sure that s390int_to_s390irq() now directly returns -EINVAL for unknown interrupt types, so that we immediately get a proper error code in case we add more interrupt types to do_inject_vcpu() without updating s390int_to_s390irq() sometime in the future.
Cc: stable@vger.kernel.org Reviewed-by: David Hildenbrand david@redhat.com Reviewed-by: Christian Borntraeger borntraeger@de.ibm.com Reviewed-by: Janosch Frank frankja@linux.ibm.com Signed-off-by: Thomas Huth thuth@redhat.com Link: https://lore.kernel.org/kvm/20190912115438.25761-1-thuth@redhat.com Signed-off-by: Christian Borntraeger borntraeger@de.ibm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/s390/kvm/interrupt.c | 10 ++++++++++ arch/s390/kvm/kvm-s390.c | 2 +- 2 files changed, 11 insertions(+), 1 deletion(-)
--- a/arch/s390/kvm/interrupt.c +++ b/arch/s390/kvm/interrupt.c @@ -1487,6 +1487,16 @@ int s390int_to_s390irq(struct kvm_s390_i case KVM_S390_MCHK: irq->u.mchk.mcic = s390int->parm64; break; + case KVM_S390_INT_PFAULT_INIT: + irq->u.ext.ext_params = s390int->parm; + irq->u.ext.ext_params2 = s390int->parm64; + break; + case KVM_S390_RESTART: + case KVM_S390_INT_CLOCK_COMP: + case KVM_S390_INT_CPU_TIMER: + break; + default: + return -EINVAL; } return 0; } --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -2541,7 +2541,7 @@ long kvm_arch_vcpu_ioctl(struct file *fi } case KVM_S390_INTERRUPT: { struct kvm_s390_interrupt s390int; - struct kvm_s390_irq s390irq; + struct kvm_s390_irq s390irq = {};
r = -EFAULT; if (copy_from_user(&s390int, argp, sizeof(s390int)))