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Message-Id: <20220427155408.19352-5-sashal@kernel.org>
Date: Wed, 27 Apr 2022 11:54:01 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
Sasha Levin <sashal@...nel.org>, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
x86@...nel.org, kvm@...r.kernel.org
Subject: [PATCH MANUALSEL 5.17 5/7] KVM: x86/mmu: avoid NULL-pointer dereference on page freeing bugs
From: Paolo Bonzini <pbonzini@...hat.com>
[ Upstream commit 9191b8f0745e63edf519e4a54a4aaae1d3d46fbd ]
WARN and bail if KVM attempts to free a root that isn't backed by a shadow
page. KVM allocates a bare page for "special" roots, e.g. when using PAE
paging or shadowing 2/3/4-level page tables with 4/5-level, and so root_hpa
will be valid but won't be backed by a shadow page. It's all too easy to
blindly call mmu_free_root_page() on root_hpa, be nice and WARN instead of
crashing KVM and possibly the kernel.
Reviewed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
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 7f009ebb319a..e7cd16e1e0a0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3239,6 +3239,8 @@ 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);
--
2.35.1
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