linux-kernel - Re: [PATCH v2 6/7] KVM: VMX: Check Intel PT related CPUID leaves

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:   Mon, 18 Oct 2021 14:47:45 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     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
Subject: Re: [PATCH v2 6/7] KVM: VMX: Check Intel PT related CPUID leaves

On 10/09/21 03:59, Xiaoyao Li wrote:
>> 
>> Ugh, looking at the rest of the code, even this isn't sufficient
>> because pt_desc.guest.addr_{a,b} are hardcoded at 4 entries, i.e.
>> running KVM on hardware with >4 entries will lead to buffer
>> overflows.
> 
> it's hardcoded to 4 because there is a note of "no processors support
>  more than 4 address ranges" in SDM vol.3 Chapter 31.3.1, table
> 31-11

True, but I agree with Sean that it's not pretty.

>> One option would be to bump that to the theoretical max of 15,
>> which doesn't seem too horrible, especially if pt_desc as a whole
>> is allocated on-demand, which it probably should be since it isn't
>> exactly tiny (nor ubiquitous)
>> 
>> A different option would be to let userspace define whatever it
>> wants for guest CPUID, and instead cap nr_addr_ranges at
>> min(host.cpuid, guest.cpuid, RTIT_ADDR_RANGE).

This is the safest option.

Paolo