linux-kernel - Re: [PATCH v10 02/19] KVM: s390: pv: handle secure storage violations for protected guests

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 6 May 2022 13:33:26 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Thomas Huth <thuth@...hat.com>
Cc:     kvm@...r.kernel.org, borntraeger@...ibm.com, frankja@...ux.ibm.com,
        pasic@...ux.ibm.com, david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, scgl@...ux.ibm.com,
        mimu@...ux.ibm.com, nrb@...ux.ibm.com
Subject: Re: [PATCH v10 02/19] KVM: s390: pv: handle secure storage
 violations for protected guests

On Thu, 5 May 2022 19:10:39 +0200
Thomas Huth <thuth@...hat.com> wrote:

> On 14/04/2022 10.02, Claudio Imbrenda wrote:
> > With upcoming patches, protected guests will be able to trigger secure
> > storage violations in normal operation.
> > 
> > A secure storage violation is triggered when a protected guest tries to
> > access secure memory that has been mapped erroneously, or that belongs
> > to a different protected guest or to the ultravisor.
> > 
> > With upcoming patches, protected guests will be able to trigger secure
> > storage violations in normal operation.  
> 
> You've already used this sentence as 1st sentence of the patch description. 
> Looks weird to read it again. Maybe scratch the 1st sentence?

oops!

> 
> > This happens for example if a
> > protected guest is rebooted with lazy destroy enabled and the new guest
> > is also protected.
> > 
> > When the new protected guest touches pages that have not yet been
> > destroyed, and thus are accounted to the previous protected guest, a
> > secure storage violation is raised.
> > 
> > This patch adds handling of secure storage violations for protected
> > guests.
> > 
> > This exception is handled by first trying to destroy the page, because
> > it is expected to belong to a defunct protected guest where a destroy
> > should be possible. If that fails, a normal export of the page is
> > attempted.
>  >
> > Therefore, pages that trigger the exception will be made non-secure
> > before attempting to use them again for a different secure guest.  
> 
> I'm an complete ignorant here, but isn't this somewhat dangerous? Could it 
> happen that a VM could destroy/export the pages of another secure guest that 
> way?

this is a good question, perhaps I should add a comment explaining that
the destroy page UVC will only work on protected VMs with no CPUs.

Exporting instead is not an issue, if/when the page is needed, it will
get imported again. Unless some things went really wrong, but that can
only happen in case of a bug in the hypervisor.

> 
>   Thomas
>