linux-kernel - Re: [PATCH v2] KVM: VMX: Fix rflags cache during vCPU reset

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Message-ID: <049b65c8-63a2-4c67-b66f-3b063038e3f8@redhat.com>
Date:   Tue, 5 Dec 2017 14:54:02 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, Jim Mattson <jmattson@...gle.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2] KVM: VMX: Fix rflags cache during vCPU reset

On 05/12/2017 01:53, Wanpeng Li wrote:
>> That seems like a convoluted path to produce an illegal RFLAGS value.
>> What's to prevent syzkaller from simply clearing bit 1 of RFLAGS with
>> the KVM_SET_REGS ioctl?
> Yeah, it can happen. Which do you prefer, ioctl fails or |
> X86_EFLAGS_FIXED unconditionally in the ioctl handler in kvm?

I suspect somebody might be passing an all-zero regs struct to
KVM_SET_REGS, so ORing X86_EFLAGS_FIXED is better.

Thanks,

Paolo