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KVM: x86/mmu: avoid NULL-pointer dereference on page freeing bugs

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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@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2022-02-08 19:08:33 -05:00
parent 57cb3bb0dc
commit 9191b8f074
1 changed files with 2 additions and 0 deletions
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2
arch/x86/kvm/mmu/mmu.c
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@ -3206,6 +3206,8 @@ 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);