Commit b5d12744 authored by Janis Schoetterl-Glausch's avatar Janis Schoetterl-Glausch Committed by Heiko Carstens
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KVM: s390: Fix lockdep issue in vm memop 



Issuing a memop on a protected vm does not make sense,
neither is the memory readable/writable, nor does it make sense to check
storage keys. This is why the ioctl will return -EINVAL when it detects
the vm to be protected. However, in order to ensure that the vm cannot
become protected during the memop, the kvm->lock would need to be taken
for the duration of the ioctl. This is also required because
kvm_s390_pv_is_protected asserts that the lock must be held.
Instead, don't try to prevent this. If user space enables secure
execution concurrently with a memop it must accecpt the possibility of
the memop failing.
Still check if the vm is currently protected, but without locking and
consider it a heuristic.

Fixes: ef11c946 ("KVM: s390: Add vm IOCTL for key checked guest absolute memory access")
Signed-off-by: default avatarJanis Schoetterl-Glausch <scgl@linux.ibm.com>
Reviewed-by: default avatarJanosch Frank <frankja@linux.ibm.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20220322153204.2637400-1-scgl@linux.ibm.com


Signed-off-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent 8b202ee2

arch/s390/kvm/kvm-s390.c

+10 −1
Original line number Diff line number Diff line
@@ -2384,7 +2384,16 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop) 
		return -EINVAL;

	if (mop->size > MEM_OP_MAX_SIZE)

		return -E2BIG;

	if (kvm_s390_pv_is_protected(kvm))

	/*

	 * This is technically a heuristic only, if the kvm->lock is not

	 * taken, it is not guaranteed that the vm is/remains non-protected.

	 * This is ok from a kernel perspective, wrongdoing is detected

	 * on the access, -EFAULT is returned and the vm may crash the

	 * next time it accesses the memory in question.

	 * There is no sane usecase to do switching and a memop on two

	 * different CPUs at the same time.

	 */

	if (kvm_s390_pv_get_handle(kvm))

		return -EINVAL;

	if (mop->flags & KVM_S390_MEMOP_F_SKEY_PROTECTION) {

		if (access_key_invalid(mop->key))