linux-kernel - [PATCH 5/5] KVM: x86: mmu: Add guest physical address check in translate

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Message-Id: <20200227172306.21426-6-mgamal@redhat.com>
Date:   Thu, 27 Feb 2020 19:23:06 +0200
From:   Mohammed Gamal <mgamal@...hat.com>
To:     kvm@...r.kernel.org, pbonzini@...hat.com
Cc:     sean.j.christopherson@...el.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        linux-kernel@...r.kernel.org, Mohammed Gamal <mgamal@...hat.com>
Subject: [PATCH 5/5] KVM: x86: mmu: Add guest physical address check in translate_gpa()

In case of running a guest with 4-level page tables on a 5-level page
table host, it might happen that a guest might have a physical address
with reserved bits set, but the host won't see that and trap it.

Hence, we need to check page faults' physical addresses against the guest's
maximum physical memory and if it's exceeded, we need to add
the PFERR_RSVD_MASK bits to the PF's error code.

Also make sure the error code isn't overwritten by the page table walker.

Signed-off-by: Mohammed Gamal <mgamal@...hat.com>
---
 arch/x86/kvm/mmu/mmu.c         | 4 ++++
 arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 099643edfdeb..994e8377b65f 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -523,6 +523,10 @@ static bool check_mmio_spte(struct kvm_vcpu *vcpu, u64 spte)
 static gpa_t translate_gpa(struct kvm_vcpu *vcpu, gpa_t gpa, u32 access,
                                   struct x86_exception *exception)
 {
+	/* Check if guest physical address doesn't exceed guest maximum */
+	if (gpa >= (1ull << cpuid_maxphyaddr(vcpu)))
+		exception->error_code |= PFERR_RSVD_MASK;
+
         return gpa;
 }
 
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index e4c8a4cbf407..aa3db722604b 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -476,7 +476,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
 
 	walker->fault.vector = PF_VECTOR;
 	walker->fault.error_code_valid = true;
-	walker->fault.error_code = errcode;
+	walker->fault.error_code |= errcode;
 
 #if PTTYPE == PTTYPE_EPT
 	/*
-- 
2.21.1