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

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Message-ID: <20250612044943.151258-1-pbonzini@redhat.com>
Date: Thu, 12 Jun 2025 00:49:43 -0400
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: seanjc@...gle.com,
	xiaoyao.li@...el.com,
	yan.y.zhao@...el.com
Subject: [PATCH] KVM: x86/mmu: Reject direct bits in gpa passed to KVM_PRE_FAULT_MEMORY

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