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[82.81.161.50]) by smtp.gmail.com with ESMTPSA id o5-20020ac87c45000000b003a50d92f9b4sm608578qtv.1.2022.11.03.07.06.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 07:06:45 -0700 (PDT) Message-ID: <33dfde6d609bc800edc5e813705523f6afdcedf0.camel@redhat.com> Subject: Re: [PATCH 0/9] nSVM: Security and correctness fixes From: Maxim Levitsky To: kvm@vger.kernel.org Cc: Paolo Bonzini , "H. Peter Anvin" , Shuah Khan , Yang Zhong , Wei Wang , Colton Lewis , Sean Christopherson , Jim Mattson , Chenyi Qiang , Borislav Petkov , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Dave Hansen , Ingo Molnar , David Matlack , Peter Xu , linux-kselftest@vger.kernel.org Date: Thu, 03 Nov 2022 16:06:40 +0200 In-Reply-To: <20221103135736.42295-1-mlevitsk@redhat.com> References: <20221103135736.42295-1-mlevitsk@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.4 (3.40.4-5.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Thu, 2022-11-03 at 15:57 +0200, Maxim Levitsky wrote: > Recently while trying to fix some unit tests I found a CVE in SVM nested code. > > In 'shutdown_interception' vmexit handler we call kvm_vcpu_reset. > > However if running nested and L1 doesn't intercept shutdown, we will still end > up running this function and trigger a bug in it. > > The bug is that this function resets the 'vcpu->arch.hflags' without properly > leaving the nested state, which leaves the vCPU in inconsistent state, which > later triggers a kernel panic in SVM code. > > The same bug can likely be triggered by sending INIT via local apic to a vCPU > which runs a nested guest. > > On VMX we are lucky that the issue can't happen because VMX always intercepts > triple faults, thus triple fault in L2 will always be redirected to L1. > Plus the 'handle_triple_fault' of VMX doesn't reset the vCPU. > > INIT IPI can't happen on VMX either because INIT events are masked while in > VMX mode. > > First 4 patches in this series address the above issue, and are > already posted on the list with title, > ('nSVM: fix L0 crash if L2 has shutdown condtion which L1 doesn't intercept') > I addressed the review feedback and also added a unit test to hit this issue. > > In addition to these patches I noticed that KVM doesn't honour SHUTDOWN intercept bit > of L1 on SVM, and I included a fix to do so - its only for correctness > as a normal hypervisor should always intercept SHUTDOWN. > A unit test on the other hand might want to not do so. > I also extendted the triple_fault_test selftest to hit this issue. > > Finaly I found another security issue, I found a way to > trigger a kernel non rate limited printk on SVM from the guest, and > last patch in the series fixes that. > > A unit test I posted to kvm-unit-tests project hits this issue, so > no selftest was added. > > Best regards, >         Maxim Levitsky > > Maxim Levitsky (9): >   KVM: x86: nSVM: leave nested mode on vCPU free >   KVM: x86: nSVM: harden svm_free_nested against freeing vmcb02 while >     still in use >   KVM: x86: add kvm_leave_nested >   KVM: x86: forcibly leave nested mode on vCPU reset >   KVM: selftests: move idt_entry to header >   kvm: selftests: add svm nested shutdown test >   KVM: x86: allow L1 to not intercept triple fault >   KVM: selftests: add svm part to triple_fault_test >   KVM: x86: remove exit_int_info warning in svm_handle_exit > >  arch/x86/kvm/svm/nested.c                     | 12 +++- >  arch/x86/kvm/svm/svm.c                        | 10 +-- >  arch/x86/kvm/vmx/nested.c                     |  4 +- >  arch/x86/kvm/x86.c                            | 29 ++++++-- >  tools/testing/selftests/kvm/.gitignore        |  1 + >  tools/testing/selftests/kvm/Makefile          |  1 + >  .../selftests/kvm/include/x86_64/processor.h  | 13 ++++ >  .../selftests/kvm/lib/x86_64/processor.c      | 13 ---- >  .../kvm/x86_64/svm_nested_shutdown_test.c     | 71 +++++++++++++++++++ >  .../kvm/x86_64/triple_fault_event_test.c      | 71 ++++++++++++++----- >  10 files changed, 174 insertions(+), 51 deletions(-) >  create mode 100644 tools/testing/selftests/kvm/x86_64/svm_nested_shutdown_test.c > > -- > 2.34.3 > > I jumped the gun a bit with this patch series, there are few checkpatch.pl issues and some leftovers I didn't remove. I'll resend this shortly. Best regards, Maxim Levitsky