From: Cornelia Huck <cohuck@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
David Hildenbrand <david@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com
Subject: Re: [PATCH 1/2] KVM: Check validity of resolved slot when searching memslots
Date: Wed, 8 Apr 2020 09:04:36 +0200 [thread overview]
Message-ID: <20200408090436.2bd1f303.cohuck@redhat.com> (raw)
In-Reply-To: <20200408064059.8957-2-sean.j.christopherson@intel.com>
On Tue, 7 Apr 2020 23:40:58 -0700
Sean Christopherson <sean.j.christopherson@intel.com> wrote:
> Check that the resolved slot (somewhat confusingly named 'start') is a
> valid/allocated slot before doing the final comparison to see if the
> specified gfn resides in the associated slot. The resolved slot can be
> invalid if the binary search loop terminated because the search index
> was incremented beyond the number of used slots.
>
> This bug has existed since the binary search algorithm was introduced,
> but went unnoticed because KVM statically allocated memory for the max
> number of slots, i.e. the access would only be truly out-of-bounds if
> all possible slots were allocated and the specified gfn was less than
> the base of the lowest memslot. Commit 36947254e5f98 ("KVM: Dynamically
> size memslot array based on number of used slots") eliminated the "all
> possible slots allocated" condition and made the bug embarrasingly easy
> to hit.
>
> Fixes: 9c1a5d38780e6 ("kvm: optimize GFN to memslot lookup with large slots amount")
> Reported-by: syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> include/linux/kvm_host.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 6d58beb65454..01276e3d01b9 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1048,7 +1048,7 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn)
> start = slot + 1;
> }
>
> - if (gfn >= memslots[start].base_gfn &&
> + if (start < slots->used_slots && gfn >= memslots[start].base_gfn &&
> gfn < memslots[start].base_gfn + memslots[start].npages) {
> atomic_set(&slots->lru_slot, start);
> return &memslots[start];
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
next prev parent reply other threads:[~2020-04-08 7:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-08 6:40 [PATCH 0/2] KVM: Fix out-of-bounds memslot access Sean Christopherson
2020-04-08 6:40 ` [PATCH 1/2] KVM: Check validity of resolved slot when searching memslots Sean Christopherson
2020-04-08 7:04 ` Cornelia Huck [this message]
2020-04-08 6:40 ` [PATCH 2/2] KVM: s390: Return last valid slot if approx index is out-of-bounds Sean Christopherson
2020-04-08 7:10 ` Cornelia Huck
2020-04-08 9:08 ` Paolo Bonzini
2020-04-08 7:28 ` Christian Borntraeger
2020-04-08 10:21 ` Claudio Imbrenda
2020-04-08 11:33 ` Paolo Bonzini
2020-04-08 11:40 ` Christian Borntraeger
2020-04-08 6:55 ` [PATCH 0/2] KVM: Fix out-of-bounds memslot access Christian Borntraeger
2020-04-08 7:24 ` Christian Borntraeger
2020-04-08 8:10 ` Cornelia Huck
2020-04-08 14:23 ` Sean Christopherson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200408090436.2bd1f303.cohuck@redhat.com \
--to=cohuck@redhat.com \
--cc=borntraeger@de.ibm.com \
--cc=david@redhat.com \
--cc=frankja@linux.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=sean.j.christopherson@intel.com \
--cc=syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).