linux-kernel - Re: [PATCH] KVM: x86/mmu: Reject direct bits in gpa passed to KVM_PRE_FAULT

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Message-ID: <aEuURZ1sBmSYtX9P@yzhao56-desk.sh.intel.com>
Date: Fri, 13 Jun 2025 11:00:21 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<seanjc@...gle.com>, <xiaoyao.li@...el.com>
Subject: Re: [PATCH] KVM: x86/mmu: Reject direct bits in gpa passed to
 KVM_PRE_FAULT_MEMORY

On Thu, Jun 12, 2025 at 12:49:43AM -0400, Paolo Bonzini wrote:
> Only let userspace pass the same addresses that were used in KVM_SET_USER_MEMORY_REGION
> (or KVM_SET_USER_MEMORY_REGION2); gpas in the the upper half of the address space
> are an implementation detail of TDX and KVM.
> 
> Extracted from a patch by Sean Christopherson <seanjc@...gle.com>.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a4040578b537..4e06e2e89a8f 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4903,6 +4903,9 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
>  	if (!vcpu->kvm->arch.pre_fault_allowed)
>  		return -EOPNOTSUPP;
>  
> +	if (kvm_is_gfn_alias(vcpu->kvm, gpa_to_gfn(range->gpa)))
> +		return -EINVAL;
> +
Do we need the same check in kvm_vm_ioctl_set_mem_attributes()?

>  	/*
>  	 * reload is efficient when called repeatedly, so we can do it on
>  	 * every iteration.
> -- 
> 2.43.5
>