On Tue, Aug 03, 2021 at 04:55:19PM +0300, Ovidiu Panait wrote:
From: Paolo Bonzini pbonzini@redhat.com
commit bd2fae8da794b55bf2ac02632da3a151b10e664c upstream.
In order to convert an HVA to a PFN, KVM usually tries to use the get_user_pages family of functinso. This however is not possible for VM_IO vmas; in that case, KVM instead uses follow_pfn.
In doing this however KVM loses the information on whether the PFN is writable. That is usually not a problem because the main use of VM_IO vmas with KVM is for BARs in PCI device assignment, however it is a bug. To fix it, use follow_pte and check pte_write while under the protection of the PTE lock. The information can be used to fail hva_to_pfn_remapped or passed back to the caller via *writable.
Usage of follow_pfn was introduced in commit add6a0cd1c5b ("KVM: MMU: try to fix up page faults before giving up", 2016-07-05); however, even older version have the same issue, all the way back to commit 2e2e3738af33 ("KVM: Handle vma regions with no backing page", 2008-07-20), as they also did not check whether the PFN was writable.
Fixes: 2e2e3738af33 ("KVM: Handle vma regions with no backing page") Reported-by: David Stevens stevensd@google.com Cc: 3pvd@google.com Cc: Jann Horn jannh@google.com Cc: Jason Gunthorpe jgg@ziepe.ca Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com [OP: backport to 4.14, adjust follow_pte() -> follow_pte_pmd()] Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com
virt/kvm/kvm_main.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
All now queued up, thanks.
greg k-h