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KVM: s390: Do not leak kernel stack data in the KVM_S390_INTERRUPT ioctl

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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>
This commit is contained in:
Thomas Huth 2019-09-12 13:54:38 +02:00 committed by Christian Borntraeger
parent 13a17cc052
commit 53936b5bf3
2 changed files with 11 additions and 1 deletions
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10
arch/s390/kvm/interrupt.c
View File

@ -1961,6 +1961,16 @@ int s390int_to_s390irq(struct kvm_s390_interrupt *s390int,
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;
}

2
arch/s390/kvm/kvm-s390.c
View File

@ -4335,7 +4335,7 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
}
case KVM_S390_INTERRUPT: {
struct kvm_s390_interrupt s390int;
struct kvm_s390_irq s390irq;
struct kvm_s390_irq s390irq = {};
if (copy_from_user(&s390int, argp, sizeof(s390int)))
return -EFAULT;