linux-kernel - Re: [RFCv2 00/16] KVM protected memory extension

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Message-ID: <87sga52lse.fsf@vitty.brq.redhat.com>
Date:   Fri, 23 Oct 2020 14:01:53 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>,
        "Edgecombe\, Rick P" <rick.p.edgecombe@...el.com>,
        "Kleen\, Andi" <andi.kleen@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, x86@...nel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [RFCv2 00/16] KVM protected memory extension

"Kirill A. Shutemov" <kirill@...temov.name> writes:

> On Wed, Oct 21, 2020 at 04:46:48PM +0200, Vitaly Kuznetsov wrote:
>> "Kirill A. Shutemov" <kirill@...temov.name> writes:
>> 
>> > Maybe it would be cleaner to handle reboot in userspace? If we got the VM
>> > rebooted, just reconstruct it from scratch as if it would be new boot.
>> 
>> We are definitely not trying to protect against malicious KVM so maybe
>> we can do the cleanup there (when protection was enabled) so we can
>> unprotect everything without risk of a leak?
>
> Do you have any particular codepath in mind? I didn't find anything
> suitable so far.

I didn't put much thought in it but e.g. on x86, what if we put this to
kvm_vcpu_reset() under 'if (kvm_vcpu_is_bsp())' condition? 

The main problem I see is that we can't clean up *all* memory,
e.g. firmware related stuff should stay intact and this contraducts your
KVM_HC_ENABLE_MEM_PROTECTED which protects everything. We can, probably,
get rid of it leaving KVM_HC_MEM_SHARE/KVM_HC_MEM_UNSHARE only shifting
responsibility to define what can be cleaned up on the guest kernel
(stating in the doc that all protected memory will get whiped out on
reboot).

-- 
Vitaly