linux-kernel - Re: [PATCH 3/6] KVM: x86: Add dedicated emulator helper for grabbing CPUID.maxphyaddr

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]

Date:   Wed, 4 Mar 2020 12:47:40 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jan Kiszka <jan.kiszka@...mens.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 3/6] KVM: x86: Add dedicated emulator helper for grabbing
 CPUID.maxphyaddr

On Tue, Mar 03, 2020 at 11:14:22AM +0100, Paolo Bonzini wrote:
> On 03/03/20 10:48, Jan Kiszka wrote:
> >>
> >> I don't think this is a particularly useful change.  Yes, it's not
> >> intuitive but is it more than a matter of documentation (and possibly
> >> moving the check_cr_write snippet into a separate function)?
> > 
> > Besides the non obvious return value of the current function, this
> > approach also avoids leaving cpuid traces for querying maxphyaddr, which
> > is also not very intuitive IMHO.
> 
> There are already other cases where we leave CPUID traces.  We can just
> stop tracing if check_limit (which should be renamed to from_guest) is
> true; there are other internal cases which call ctxt->ops->get_cpuid,
> such as vendor_intel, and those should also use check_limit==true and
> check the return value of ctxt->ops->get_cpuid.

No, the vendor checks that use get_cpuid() shouldn't do check_limit=true,
they're looking for an exact match on the vendor.

Not that it matters.  @check_limit only comes into play on a vendor check
if CPUID.0 doesn't exist, and @check_limit only effects the output if
CPUID.0 _does_ exist.  I.e. the output for CPUID.0 is unaffected by
@check_limit.