linux-kernel - Re: [PATCH] x86/kvm/nVMCS: fix VMCLEAR when Enlightened VMCS is in use

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 for Android: free password hash cracker in your pocket

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

Message-ID: <87lfxqdp3n.fsf@vitty.brq.redhat.com>
Date:   Tue, 25 Jun 2019 10:51:56 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Liran Alon <liran.alon@...cle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] x86/kvm/nVMCS: fix VMCLEAR when Enlightened VMCS is in use

Liran Alon <liran.alon@...cle.com> writes:

>> On 24 Jun 2019, at 16:30, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>> 
>> 
>> +bool nested_enlightened_vmentry(struct kvm_vcpu *vcpu, u64 *evmptr)
>
> I prefer to rename evmptr to evmcs_ptr. I think it’s more readable and sufficiently short.
> In addition, I think you should return either -1ull or assist_page.current_nested_vmcs.
> i.e. Don’t return evmcs_ptr by pointer but instead as a return-value
> and get rid of the bool.

Actually no, sorry, I'm having second thoughts here: in handle_vmclear()
we don't care about the value of evmcs_ptr, we only want to check that
enlightened vmentry bit is enabled in assist page. If we switch to
checking evmcs_ptr against '-1', for example, we will make '-1' a magic
value which is not in the TLFS. Windows may decide to use it for
something else - and we will get a hard-to-debug bug again.

If you still dislike nested_enlightened_vmentry() having the side effect
of fetching evmcs_ptr I can get rid of it by splitting the function into
two, however, it will be less efficient for
nested_vmx_handle_enlightened_vmptrld(). Or we can just leave things as
they are there and use the newly introduced function in handle_vmclear()
only.

-- 
Vitaly