linux-kernel - Re: [PATCH 0/9] Intel Processor Trace virtulization enabling

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5b434733-c974-9012-0e08-48ed9e1d2fa6@redhat.com>
Date:   Wed, 18 Oct 2017 13:22:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Kang, Luwei" <luwei.kang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chao Peng <chao.p.peng@...ux.intel.com>
Subject: Re: [PATCH 0/9] Intel Processor Trace virtulization enabling

On 18/10/2017 13:06, Kang, Luwei wrote:
>>>> Nested virtualization is interesting.  We would like the nested
>>>> hypervisor to be forced to set the "use GPA for processor tracing"
>>>> secondary execution control whenever "enable EPT" is set and RTIT_CTL
>>>> is nonzero.  There is no way to encode that in
>>>> IA32_VMX_PROCBASED_CTLS2, however.  It would be nice if Intel could
>>>> reserve a bit in IA32_VMX_EPT_VPID_CAP for KVM to express that
>>>> constraint.
>>>
>>> Do you mean if nested hypervisor get the capability of "Guest PT use
>>> GPA" and EPT has enable. Highly recommend nested hypervisor set "
>>> Guest PT use GPA " as well.
>>
>> Well, it's required more than recommended.  However, it's only required if "enable EPT" is set and RTIT_CTL is nonzero.
>>
>>> If nested hypervisor is also KVM, "use GPA for processor tracing"
>>> will be set for sure. But other hypervisor may not do that. So, we'd
>>> better add a flag in IA32_VMX_EPT_VPID_CAP to express that constraint.
>>
>> Correct.  The constraint would be:
>>
>> * RTIT_CTL on entry is zero if EPT is disabled
>>
>> * RTIT_CTL on entry is zero if EPT is enabled and "Guest PT uses GPA" is zero
>>
>> Maybe IA32_VMX_EPT_VPID_CAP is not the best place.  I'll let Intel decide that.
> 
> Get it. I have feedback to hardware architect. I hope it can be applied but it may need wait a long time.

Note that the hardware need not do anything.  However it would be nice
if the SDM can define a bit _for the hypervisors_ to enforce the above
constraint and fail vmentry if they are not respected.

Paolo