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SubjectRe: [PATCH 1/2] KVM: X86: Fix CR3 reserve bits
2018-05-13 15:53 GMT+08:00 Liran Alon <liran.alon@oracle.com>:
>
> ----- kernellwp@gmail.com wrote:
>
>> From: Wanpeng Li <wanpengli@tencent.com>
>>
>> MSB of CR3 is a reserved bit if the PCIDE bit is not set in CR4.
>> It should be checked when PCIDE bit is not set, however commit
>> 'd1cd3ce900441 ("KVM: MMU: check guest CR3 reserved bits based on
>> its physical address width")' removes the bit 63 checking
>> unconditionally. This patch fixes it by checking bit 63 of CR3
>> when PCIDE bit is not set in CR4.
>>
>> Fixes: d1cd3ce900441 (KVM: MMU: check guest CR3 reserved bits based on
>> its physical address width)
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <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(-)
>>
>> 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)
>> maxphyaddr = eax & 0xff;
>> else
>> maxphyaddr = 36;
>> - rsvd = rsvd_bits(maxphyaddr, 62);
>> + if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE)
>> + new_val &= ~CR3_PCID_INVD;
>> + rsvd = rsvd_bits(maxphyaddr, 63);
>
> I would prefer instead to do this:
> if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE)
> rsvd &= ~CR3_PCID_INVD;
> It makes more sense as opposed to temporary removing the CR3_PCID_INVD bit from new_val.

It tries the same way
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c19986fea873f3c745122bf79013a872a190f212
pointed out.

Regards,
Wanpeng Li

>
>> }
>>
>> if (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)
>> }
>>
>> if (is_long_mode(vcpu) &&
>> - (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 62)))
>> + (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
>> return 1;
>> else if (is_pae(vcpu) && is_paging(vcpu) &&
>> !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
>> --
>> 2.7.4

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