From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Jim Mattson <jmattson@google.com>,
syzbot <syzbot+e87846c48bf72bc85311@syzkaller.appspotmail.com>,
Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: UBSAN: shift-out-of-bounds in kvm_vcpu_after_set_cpuid
Date: Tue, 12 Jan 2021 08:53:59 -0800 [thread overview]
Message-ID: <X/3UJ7EtyAb2Ww+6@google.com> (raw)
In-Reply-To: <f1aa1f3c-1dac-2357-ee1c-ab505513382f@redhat.com>
On Tue, Jan 12, 2021, Paolo Bonzini wrote:
> 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.
No, that wouldn't have fixed this specific bug. In this case, the issue was
CPUID.80000008H:AL == 0; masking off bits 7:6 wouldn't have changed anything.
And, masking bits 7:6 is architecturally wrong. Both the SDM and APM state that
bits 7:0 contain the number of PA bits.
KVM could reject guest.MAXPA > host.MAXPA, but arbitrarily dropping bits would
be wrong.
next prev parent reply other threads:[~2021-01-12 16:54 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-22 8:36 UBSAN: shift-out-of-bounds in kvm_vcpu_after_set_cpuid syzbot
2021-01-11 22:44 ` Jim Mattson
2021-01-11 23:01 ` Sean Christopherson
2021-01-12 8:06 ` Paolo Bonzini
2021-01-12 16:53 ` Sean Christopherson [this message]
2021-01-13 14:20 ` Paolo Bonzini
2021-01-13 16:46 ` Sean Christopherson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=X/3UJ7EtyAb2Ww+6@google.com \
--to=seanjc@google.com \
--cc=bp@alien8.de \
--cc=hpa@zytor.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=syzbot+e87846c48bf72bc85311@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).