Re: [PATCH MANUALSEL 5.15 6/7] KVM: x86/mmu: avoid NULL-pointer dereference on page freeing bugs

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 4/27/22 17:54, Sasha Levin wrote:
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
  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 34e828badc51..806f9d42bcce 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3314,6 +3314,8 @@ 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);

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>




[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux