2017-06-07 17:54 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>:
> 2017-06-07 17:14 GMT+08:00 Moguofang (Dennis mo) <moguofang@xxxxxxxxxx>:
>> the patch fixed the oob vulnerability when i = 79, but maybe the patch introduces an infinite loop, if i = 79, then j = 0, the do-while loop use cpuid_entries[0-78] to compare cpuid_entries[79], maybe fall into infinite loop.
>
> It will not happen, if i == j, then ej->function == e->function and
> for loop exit.
>
> Anyway, another method is:
>
> - for (j = i + 1; ; j = (j + 1) % nent) {
> + for (j = (i + 1) % nent; ; j = (j + 1) % nent) {
Paolo, which one do you prefer?
Regards,
Wanpeng Li
>>
>> Kind regards
>> moguofang
>>
>> -----邮件原件-----
>> 发件人: Wanpeng Li [mailto:kernellwp@xxxxxxxxx]
>> 发送时间: 2017年6月7日 16:32
>> 收件人: Moguofang (Dennis mo)
>> 抄送: kvm@xxxxxxxxxxxxxxx; Zhouyu (Axis Zhou, ICSL)
>> 主题: Re: KVM vulnerability report about cpuid instruction
>>
>> 2017-06-07 15:09 GMT+08:00 Moguofang (Dennis mo) <moguofang@xxxxxxxxxx>:
>>> Hello!
>>> A new vulnerability discover by me.
>>
>> Could you test something like this?
>>
>> --------------------------->8-------------------------------------------
>> --------------------------->------------------
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index a181ae7..b927a42 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -779,19 +779,20 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
>>
>> static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i) {
>> + int j = i, nent = vcpu->arch.cpuid_nent;
>> struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
>> - int j, nent = vcpu->arch.cpuid_nent;
>> + struct kvm_cpuid_entry2 *ej;
>>
>> e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
>> /* when no next entry is found, the current entry[i] is reselected */
>> - for (j = i + 1; ; j = (j + 1) % nent) {
>> - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
>> - if (ej->function == e->function) {
>> - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
>> - return j;
>> - }
>> - }
>> - return 0; /* silence gcc, even though control never reaches here */
>> + do {
>> + j = (j + 1) % nent;
>> + ej = &vcpu->arch.cpuid_entries[j];
>> + } while(ej->function != e->function);
>> +
>> + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
>> +
>> + return j;
>> }
>>
>> /* find an entry with matching function, matching index (if needed), and that
