linux-kernel - Re: UBSAN: shift-out-of-bounds in kvm_vcpu_after_set

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Date:   Tue, 12 Jan 2021 09:06:07 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     syzbot <syzbot+e87846c48bf72bc85311@...kaller.appspotmail.com>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: UBSAN: shift-out-of-bounds in kvm_vcpu_after_set_cpuid

On 12/01/21 00:01, Sean Christopherson wrote:
>> Perhaps cpuid_query_maxphyaddr() should just look at the low 5 bits of
>> CPUID.80000008H:EAX?

The low 6 bits I guess---yes, that would make sense and it would have 
also fixed the bug.

(Nevertheless it's a good idea to make rsvd_bits more robust as well, as 
in the commit that Sean referenced.

Paolo