On 24/06/21 05:57, David Stevens wrote:
KVM supports mapping VM_IO and VM_PFNMAP memory into the guest by using follow_pte in gfn_to_pfn. However, the resolved pfns may not have assoicated struct pages, so they should not be passed to pfn_to_page. This series removes such calls from the x86 and arm64 secondary MMU. To do this, this series modifies gfn_to_pfn to return a struct page in addition to a pfn, if the hva was resolved by gup. This allows the caller to call put_page only when necessated by gup. This series provides a helper function that unwraps the new return type of gfn_to_pfn to provide behavior identical to the old behavior. As I have no hardware to test powerpc/mips changes, the function is used there for minimally invasive changes. Additionally, as gfn_to_page and gfn_to_pfn_cache are not integrated with mmu notifier, they cannot be easily changed over to only use pfns. This addresses CVE-2021-22543 on x86 and arm64.
Thank you very much for this. I agree that it makes sense to have a minimal change; I had similar changes almost ready, but was stuck with deadlocks in the gfn_to_pfn_cache case. In retrospect I should have posted something similar to your patches.
I have started reviewing the patches, and they look good. I will try to include them in 5.13.
Paolo
