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[88.21.202.17]) by smtp.gmail.com with ESMTPSA id p8sm21067366wre.11.2020.05.12.00.54.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 May 2020 00:54:28 -0700 (PDT) Subject: Re: [PATCH] i386/kvm: fix a use-after-free when vcpu plug/unplug To: Pan Nengyuan , pbonzini@redhat.com, rth@twiddle.net, ehabkost@redhat.com, mtosatti@redhat.com Cc: euler.robot@huawei.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, zhang.zhanghailiang@huawei.com References: <20200512133933.8696-1-pannengyuan@huawei.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Tue, 12 May 2020 09:54:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200512133933.8696-1-pannengyuan@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 5/12/20 3:39 PM, Pan Nengyuan wrote: > When we hotplug vcpus, cpu_update_state is added to vm_change_state_head > in kvm_arch_init_vcpu(). But it forgot to delete in kvm_arch_destroy_vcpu() after > unplug. Then it will cause a use-after-free access. This patch delete it in > kvm_arch_destroy_vcpu() to fix that. > > Reproducer: > virsh setvcpus vm1 4 --live > virsh setvcpus vm1 2 --live > virsh suspend vm1 > virsh resume vm1 > > The UAF stack: > ==qemu-system-x86_64==28233==ERROR: AddressSanitizer: heap-use-after-free on address 0x62e00002e798 at pc 0x5573c6917d9e bp 0x7fff07139e50 sp 0x7fff07139e40 > WRITE of size 1 at 0x62e00002e798 thread T0 > #0 0x5573c6917d9d in cpu_update_state /mnt/sdb/qemu/target/i386/kvm.c:742 > #1 0x5573c699121a in vm_state_notify /mnt/sdb/qemu/vl.c:1290 > #2 0x5573c636287e in vm_prepare_start /mnt/sdb/qemu/cpus.c:2144 > #3 0x5573c6362927 in vm_start /mnt/sdb/qemu/cpus.c:2150 > #4 0x5573c71e8304 in qmp_cont /mnt/sdb/qemu/monitor/qmp-cmds.c:173 > #5 0x5573c727cb1e in qmp_marshal_cont qapi/qapi-commands-misc.c:835 > #6 0x5573c7694c7a in do_qmp_dispatch /mnt/sdb/qemu/qapi/qmp-dispatch.c:132 > #7 0x5573c7694c7a in qmp_dispatch /mnt/sdb/qemu/qapi/qmp-dispatch.c:175 > #8 0x5573c71d9110 in monitor_qmp_dispatch /mnt/sdb/qemu/monitor/qmp.c:145 > #9 0x5573c71dad4f in monitor_qmp_bh_dispatcher /mnt/sdb/qemu/monitor/qmp.c:234 > > Reported-by: Euler Robot > Signed-off-by: Pan Nengyuan > --- > target/i386/cpu.h | 1 + > target/i386/kvm.c | 5 ++++- > 2 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/target/i386/cpu.h b/target/i386/cpu.h > index e818fc712a..afbd11b7a3 100644 > --- a/target/i386/cpu.h > +++ b/target/i386/cpu.h > @@ -1631,6 +1631,7 @@ struct X86CPU { > > CPUNegativeOffsetState neg; > CPUX86State env; > + VMChangeStateEntry *vmsentry; > > uint64_t ucode_rev; > > diff --git a/target/i386/kvm.c b/target/i386/kvm.c > index 4901c6dd74..ff2848357e 100644 > --- a/target/i386/kvm.c > +++ b/target/i386/kvm.c > @@ -1770,7 +1770,7 @@ int kvm_arch_init_vcpu(CPUState *cs) > } > } > > - qemu_add_vm_change_state_handler(cpu_update_state, env); > + cpu->vmsentry = qemu_add_vm_change_state_handler(cpu_update_state, env); > > c = cpuid_find_entry(&cpuid_data.cpuid, 1, 0); > if (c) { > @@ -1883,6 +1883,9 @@ int kvm_arch_destroy_vcpu(CPUState *cs) > env->nested_state = NULL; > } > > + qemu_del_vm_change_state_handler(cpu->vmsentry); > + cpu->vmsentry = NULL; Why set it to NULL? there is no non-NULL check. Anyway if it matters to you, why not do it in qemu_del_vm_change_state_handler()? Otherwise: Reviewed-by: Philippe Mathieu-Daudé > + > return 0; > } > >