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

Paolo Bonzini
2020-03-24T11:30:50Z

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