linux-kernel - [PATCH 05/12] KVM: MMU: avoid NULL-pointer dereference on page freeing bugs

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Date:   Wed,  9 Feb 2022 12:00:13 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     vkuznets@...hat.com, mlevitsk@...hat.com, dmatlack@...gle.com,
        seanjc@...gle.com
Subject: [PATCH 05/12] KVM: MMU: avoid NULL-pointer dereference on page freeing bugs

If kvm_mmu_free_roots encounters a PAE page table where a 64-bit page
table is expected, the result is a NULL pointer dereference.  Instead
just WARN and exit.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mmu/mmu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 7b5765ced928..d0f2077bd798 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3201,6 +3201,8 @@ static void mmu_free_root_page(struct kvm *kvm, hpa_t *root_hpa,
 		return;
 
 	sp = to_shadow_page(*root_hpa & PT64_BASE_ADDR_MASK);
+	if (WARN_ON(!sp))
+		return;
 
 	if (is_tdp_mmu_page(sp))
 		kvm_tdp_mmu_put_root(kvm, sp, false);
-- 
2.31.1