Commit 9191b8f0 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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



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: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 57cb3bb0

arch/x86/kvm/mmu/mmu.c

+2 −0
Original line number Diff line number Diff line
@@ -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);