linux-kernel - Re: [PATCH 5.10 048/104] KVM: x86: cleanup CR3 reserved bits checks

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Date:   Mon, 15 Feb 2021 20:04:27 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 048/104] KVM: x86: cleanup CR3 reserved bits checks

On 15/02/21 19:46, Pavel Machek wrote:
> Hi!
> 
>> [ Upstream commit c1c35cf78bfab31b8cb455259524395c9e4c7cd6 ]
>>
>> If not in long mode, the low bits of CR3 are reserved but not enforced to
>> be zero, so remove those checks.  If in long mode, however, the MBZ bits
>> extend down to the highest physical address bit of the guest, excluding
>> the encryption bit.
>>
>> Make the checks consistent with the above, and match them between
>> nested_vmcb_checks and KVM_SET_SREGS.
> 
>> +++ b/arch/x86/kvm/x86.c
>> @@ -9558,6 +9558,8 @@ static int kvm_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
>>   		if (!(sregs->cr4 & X86_CR4_PAE)
>>   		    || !(sregs->efer & EFER_LMA))
>>   			return -EINVAL;
>> +		if (sregs->cr3 & vcpu->arch.cr3_lm_rsvd_bits)
>> +			return false;
>>   	} else {
> 
> Function has different return type between 5.10 and 5.11, so this
> needs fixing.

I'll check that c1c35cf78bfab31b8cb455259524395c9e4c7cd6 is enough and 
send either a backport of that one, or a fixed patch for <= 5.10. 
Thanks Pavel.

Paolo