linux-kernel - Re: [PATCH v1 1/2] KVM: s390: Fix incorrect usage of mmu_notifier

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Message-ID: <0bd8a969-e8e0-4eb6-97a2-300fc322f8a2@redhat.com>
Date: Tue, 5 Aug 2025 14:09:11 +0200
From: David Hildenbrand <david@...hat.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc: linux-s390@...r.kernel.org, kvm@...r.kernel.org, frankja@...ux.ibm.com,
 seiden@...ux.ibm.com, nsg@...ux.ibm.com, nrb@...ux.ibm.com,
 schlameuss@...ux.ibm.com, hca@...ux.ibm.com, mhartmay@...ux.ibm.com,
 borntraeger@...ibm.com
Subject: Re: [PATCH v1 1/2] KVM: s390: Fix incorrect usage of
 mmu_notifier_register()

On 05.08.25 13:14, Claudio Imbrenda wrote:
> If mmu_notifier_register() fails, for example because a signal was
> pending, the mmu_notifier will not be registered. But when the VM gets
> destroyed, it will get unregistered anyway and that will cause one
> extra mmdrop(), which will eventually cause the mm of the process to
> be freed too early, and cause a use-after free.
> 
> This bug happens rarely, and only when secure guests are involved.
> 
> The solution is to check the return value of mmu_notifier_register()
> and return it to the caller (ultimately it will be propagated all the
> way to userspace). In case of -EINTR, userspace will try again.
> 
> Fixes: ca2fd0609b5d ("KVM: s390: pv: add mmu_notifier")
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb