linux-kernel - Re: [PATCH 1/2] KVM: SVM: avoid infinite loop on NPF from bad address

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Date:   Tue, 8 Jun 2021 09:17:34 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Salvatore Bonaccorso <carnil@...ian.org>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        stable@...r.kernel.org, Wanpeng Li <kernellwp@...il.com>
Subject: Re: [PATCH 1/2] KVM: SVM: avoid infinite loop on NPF from bad address

On 08/06/21 06:39, Salvatore Bonaccorso wrote:
> 
> Did this simply felt through the cracks here or is it not worth
> backporting to older series? At least
> https://bugzilla.redhat.com/show_bug.cgi?id=1947982#c3  seem to
> indicate it might not be worth of if there is risk for regression if I
> understand Wanpeng Li. Is this right?

It's not particularly interesting, because the loop can be broken with 
just Ctrl-C (or any signal for that matter) and the guest was 
misbehaving anyway.  You can read from that bugzilla link my opinion on 
this "vulnerability": if you run a VM for somebody and they want to 
waste your CPU time, they can just run a while(1) loop.

It's a bug and it is caught by the kvm-unit-tests, so I marked it for 
stable at the time because it can be useful to run kvm-unit-tests on 
stable kernels and hanging is a bit impolite (the test harness has a 
timeout, but of course tests that hang have the risk missing other 
regressions).

I will review gladly a backport, but if it is just because of that CVE 
report, documenting that the vulnerability is bogus would be time spent 
better that doing and testing the backport.

Paolo