From 9191b8f0745e63edf519e4a54a4aaae1d3d46fbd Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 8 Feb 2022 19:08:33 -0500 Subject: [PATCH] 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: Sean Christopherson Signed-off-by: Paolo Bonzini --- 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 0620480b99e0..28c4d658d2ac 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -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);