linux-kernel - Re: [PATCH 0/7] KVM: Fix memslot use-after-free bug

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Message-ID: <aa19166a-a4bd-28c2-88a0-ab5b18e8f473@redhat.com>
Date:   Tue, 24 Mar 2020 12:30:37 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Qian Cai <cai@....pw>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 0/7] KVM: Fix memslot use-after-free bug

On 20/03/20 21:55, Sean Christopherson wrote:
> Fix a bug introduced by dynamic memslot allocation where the LRU slot can
> become invalid and lead to a out-of-bounds/use-after-free scenario.
> 
> The patch is different that what Qian has already tested, but I was able
> to reproduce the bad behavior by enhancing the set memory region selftest,
> i.e. I'm relatively confident the bug is fixed.
> 
> Patches 2-6 are a variety of selftest cleanup, with the aforementioned
> set memory region enhancement coming in patch 7.
> 
> Note, I couldn't get the selftest to fail outright or with KASAN, but was
> able to hit a WARN_ON an invalid slot 100% of the time (without the fix,
> obviously).
> 
> Regarding s390, I played around a bit with merging gfn_to_memslot_approx()
> into search_memslots().  Code wise it's trivial since they're basically
> identical, but doing so increases the code footprint of search_memslots()
> on x86 by 30 bytes, so I ended up abandoning the effort.
> 
> Sean Christopherson (7):
>   KVM: Fix out of range accesses to memslots
>   KVM: selftests: Fix cosmetic copy-paste error in vm_mem_region_move()
>   KVM: selftests: Take vcpu pointer instead of id in vm_vcpu_rm()
>   KVM: selftests: Add helpers to consolidate open coded list operations
>   KVM: selftests: Add util to delete memory region
>   KVM: selftests: Expose the primary memslot number to tests
>   KVM: selftests: Add "delete" testcase to set_memory_region_test
> 
>  arch/s390/kvm/kvm-s390.c                      |   3 +
>  include/linux/kvm_host.h                      |   3 +
>  .../testing/selftests/kvm/include/kvm_util.h  |   3 +
>  tools/testing/selftests/kvm/lib/kvm_util.c    | 139 ++++++++++--------
>  .../kvm/x86_64/set_memory_region_test.c       | 122 +++++++++++++--
>  virt/kvm/kvm_main.c                           |   3 +
>  6 files changed, 201 insertions(+), 72 deletions(-)
> 

Queued patches 1-3, thanks.

Paolo