From: Gi-Oh Kim <gi-oh.kim@profitbricks.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Roman Penyaev <roman.penyaev@profitbricks.com>,
Mikhail Sennikovskii <mikhail.sennikovskii@profitbricks.com>,
Gleb Natapov <gleb@kernel.org>,
kvm@vger.kernel.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present
Date: Tue, 30 May 2017 18:31:20 +0200 [thread overview]
Message-ID: <CAJX1YtaHkNtz1B_mqMJGzW56LoREWFkCHXwr9GV8dVH4ZQkniA@mail.gmail.com> (raw)
In-Reply-To: <aae2fc5e-a3ee-5f8e-60aa-7748435becf9@redhat.com>
Hi,
I found a code to set unusable flag of segment register incorrectly.
https://lkml.org/lkml/2017/5/30/459
I guess above patch and current discussion could be related.
I guess following sequence could happen.
1. svm_get_segment() sets var->unusable of Stack Segment incorrectly
2. svm_set_segment() clears both of s->attrib and svm->vmcb->save.cpl.
Is it possible scenario?
On Tue, May 30, 2017 at 6:05 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 30/05/2017 17:58, Roman Penyaev wrote:
>> Indeed, what is left is eventually take it from SS.RPL. J.
>
> Ahah! :) But I only suggested that in specific cases.
>
>> But jokes aside, with your last patch you seems fixed a race problem
>> when "CS.RPL is not equal to the CPL in the few instructions between
>> setting CR0.PE and reloading CS".
>
> Yes, exactly. The symptom was a crash (triple fault) when you kept
> interrupting with "info cpus" a guest that repeatedly went to protected
> mode and back to real mode.
>
>> We will have CPL in var->dpl, and it seems ok. All we need is not
>> to lose it on the way kernel->userspace->kernel.
>
> You're right. So what do you think of the other suggestion (svm.c
> doesn't clear attributes for unusable registers, QEMU only clears P for
> unusable registers)?
>
> Thanks,
>
> Paolo
--
Best regards,
Gi-Oh Kim
TEL: 0176 2697 8962
next prev parent reply other threads:[~2017-05-30 16:32 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-19 16:14 [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present Roman Penyaev
2017-05-21 3:31 ` Andy Lutomirski
2017-05-21 7:53 ` Roman Penyaev
2017-05-21 20:19 ` Andy Lutomirski
2017-05-24 19:19 ` Roman Penyaev
2017-05-30 14:47 ` Paolo Bonzini
2017-05-30 17:35 ` Roman Penyaev
2017-05-30 21:09 ` Paolo Bonzini
2017-05-31 10:17 ` Roman Penyaev
2017-05-31 10:50 ` Paolo Bonzini
2017-05-30 15:13 ` Paolo Bonzini
2017-05-30 15:58 ` Roman Penyaev
2017-05-30 16:05 ` Paolo Bonzini
2017-05-30 16:31 ` Gi-Oh Kim [this message]
2017-06-15 21:44 ` Andy Lutomirski
2017-06-16 8:44 ` Roman Penyaev
2017-06-16 16:40 ` Paolo Bonzini
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