linux-kernel - [PATCH] kvm: x86/mmu: Fix is_tdp_mmu

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Date:   Wed, 11 Nov 2020 10:53:37 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Peter Shier <pshier@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Zdenek Kaspar <zkaspar82@...il.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH] kvm: x86/mmu: Fix is_tdp_mmu_check when using PAE

When PAE is in use, the root_hpa will not have a shadow page assoicated
with it. In this case the kernel will crash with a NULL pointer
dereference. Add checks to ensure is_tdp_mmu_root works as intended even
when using PAE.

Tested: compiles

Fixes: 02c00b3a2f7e ("kvm: x86/mmu: Allocate and free TDP MMU roots")
Reported-by: Zdenek Kaspar <zkaspar82@...il.com>
Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 27e381c9da6c..13013f4d98ad 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -49,8 +49,18 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
 {
 	struct kvm_mmu_page *sp;
 
+	if (WARN_ON(!VALID_PAGE(hpa)))
+		return false;
+
 	sp = to_shadow_page(hpa);
 
+	/*
+	 * If this VM is being run with PAE, the TDP MMU will not be enabled
+	 * and the root HPA will not have a shadow page associated with it.
+	 */
+	if (!sp)
+		return false;
+
 	return sp->tdp_mmu_page && sp->root_count;
 }
 
-- 
2.29.2.222.g5d2a92d10f8-goog