On 5/12/2020 3:54 PM, Philippe Mathieu-Daudé wrote:
> 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 <euler.robot@xxxxxxxxxx>
>> Signed-off-by: Pan Nengyuan <pannengyuan@xxxxxxxxxx>
>> ---
>> 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()?
Yes, there is no non-NULL check and it will not be NULL at all.
Actually it doesn't matters to me, just habitually set to null after free.
I will remove it.
Thanks.
>
> Otherwise:
> Reviewed-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
>
>> +
>> return 0;
>> }
>>
>
> .
