linux-kernel - Re: [PATCH 4.19 167/211] KVM: x86: Manually calculate reserved bits when loading PDPTRS

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Date:   Mon, 11 Nov 2019 16:25:31 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Lamprecht <t.lamprecht@...xmox.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nadav Amit <nadav.amit@...il.com>,
        Doug Reiland <doug.reiland@...el.com>,
        Peter Xu <peterx@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 4.19 167/211] KVM: x86: Manually calculate reserved bits
 when loading PDPTRS

On Mon, Nov 11, 2019 at 07:08:20PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Nov 11, 2019 at 09:57:19AM -0800, Sean Christopherson wrote:
> > On Mon, Nov 11, 2019 at 06:48:59PM +0100, Greg Kroah-Hartman wrote:
> > > Thanks for figuring this out, can you send us a patch that we can apply
> > > to fix this issue in the stable tree?
> > 
> > Can do.  A custom backport will be need for 4.20 and earlier, not 4.19 and
> > earlier.  I misremembered when we did the VMX refactoring.
> > 
> > For 5.0, 5.1 and 5.2, commit bf03d4f93347 can be applied directly.
> 
> 5.0, 5.1, and 5.2 are all long end-of-life, they are not getting any
> updates and no one should be using them, so nothing to worry about
> there.

Backports sent for 4.14 and 4.19.  4.9 and 4.4 aren't affected as the bug
was introduced in 4.14. by commit d1cd3ce90044 ("KVM: MMU: check guest CR3
reserved bits based on its physical address width.").

I did send patches for 4.9 and 4.4 for another PAE bug fix that I ran into
while backporting; commit d35b34a9a70e ("kvm: mmu: Don't read PDPTEs when
paging is not enabled").  I'm not aware of bug reports, but the patch is
quite safe and should have been tagged for stable.