Re: [PATCH] KVM: x86/mmu: fix NULL pointer dereference on guest INVPCID

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, May 24, 2022 at 05:27:56PM +0200, Vegard Nossum wrote:
> 
> On 5/24/22 17:22, Greg KH wrote:
> > On Tue, May 24, 2022 at 05:11:18PM +0200, Vegard Nossum wrote:
> >> From: Paolo Bonzini <pbonzini@redhat.com>
> >>
> >> commit 9f46c187e2e680ecd9de7983e4d081c3391acc76 upstream.
> >>
> >> With shadow paging enabled, the INVPCID instruction results in a call
> >> to kvm_mmu_invpcid_gva.  If INVPCID is executed with CR0.PG=0, the
> >> invlpg callback is not set and the result is a NULL pointer dereference.
> >> Fix it trivially by checking for mmu->invlpg before every call.
> >>
> >> There are other possibilities:
> >>
> >> - check for CR0.PG, because KVM (like all Intel processors after P5)
> >>   flushes guest TLB on CR0.PG changes so that INVPCID/INVLPG are a
> >>   nop with paging disabled
> >>
> >> - check for EFER.LMA, because KVM syncs and flushes when switching
> >>   MMU contexts outside of 64-bit mode
> >>
> >> All of these are tricky, go for the simple solution.  This is CVE-2022-1789.
> >>
> >> Reported-by: Yongkang Jia <kangel@zju.edu.cn>
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> >> [fix conflict due to missing b9e5603c2a3accbadfec570ac501a54431a6bdba]
> >> Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
> >> ---
> >>  arch/x86/kvm/mmu/mmu.c | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > What kernel tree(s) are you wanting this to be applied to?
> 
> I replied to the v5.17 email
> (https://lore.kernel.org/stable/165314153515625@kroah.com/T/#u) and I've
> only tested this on top of 5.17.9.
> 
> Is that generally enough to trigger attempts to automatically
> cherry-pick it onto the older branches or should I test and submit for
> the older ones as well?

You should test and submit for the older ones as well please.

> How would you prefer to indicate the kernel tree(s) in the future?

Just say so in the [PATCH 5.17.y] subject line, or in the signed-off-by
area or below the --- line.

Responding to the email and relying on the thread alone doesn't usually
work as the original message is long gone from my mailboxes, I can't
keep that old stuff cluttering up the place :)

thanks,

greg k-h