Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
Message-ID: <dface5bf-04f4-439a-86d1-df301eec1974@default>
Date:   Sun, 13 May 2018 00:53:10 -0700 (PDT)
From:   Liran Alon <liran.alon@oracle.com>
To:     <kernellwp@gmail.com>
Cc:     <rkrcmar@redhat.com>, <pbonzini@redhat.com>,
        <linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>,
        <junaids@google.com>
Subject: Re: [PATCH 1/2] KVM: X86: Fix CR3 reserve bits
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


----- kernellwp@gmail.com wrote:

> From: Wanpeng Li <wanpengli@tencent.com>
>=20
> MSB of CR3 is a reserved bit if the PCIDE bit is not set in CR4.=20
> It should be checked when PCIDE bit is not set, however commit=20
> 'd1cd3ce900441 ("KVM: MMU: check guest CR3 reserved bits based on=20
> its physical address width")' removes the bit 63 checking=20
> unconditionally. This patch fixes it by checking bit 63 of CR3=20
> when PCIDE bit is not set in CR4.
>=20
> Fixes: d1cd3ce900441 (KVM: MMU: check guest CR3 reserved bits based on
> its physical address width)
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com>
> Cc: Junaid Shahid <junaids@google.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
>  arch/x86/kvm/emulate.c | 4 +++-
>  arch/x86/kvm/x86.c     | 2 +-
>  2 files changed, 4 insertions(+), 2 deletions(-)
>=20
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index b3705ae..b21f427 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -4189,7 +4189,9 @@ static int check_cr_write(struct
> x86_emulate_ctxt *ctxt)
>  =09=09=09=09maxphyaddr =3D eax & 0xff;
>  =09=09=09else
>  =09=09=09=09maxphyaddr =3D 36;
> -=09=09=09rsvd =3D rsvd_bits(maxphyaddr, 62);
> +=09=09=09if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE)
> +=09=09=09=09new_val &=3D ~CR3_PCID_INVD;
> +=09=09=09rsvd =3D rsvd_bits(maxphyaddr, 63);

I would prefer instead to do this:
if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE)
    rsvd &=3D ~CR3_PCID_INVD;
It makes more sense as opposed to temporary removing the CR3_PCID_INVD bit =
from new_val.

>  =09=09}
> =20
>  =09=09if (new_val & rsvd)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 87e4805..9a90668 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -863,7 +863,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned
> long cr3)
>  =09}
> =20
>  =09if (is_long_mode(vcpu) &&
> -=09    (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 62)))
> +=09    (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
>  =09=09return 1;
>  =09else if (is_pae(vcpu) && is_paging(vcpu) &&
>  =09=09   !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
> --=20
> 2.7.4