On Thu, 9 Sep 2021 18:22:39 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote: > Resend because I missed ccing people on the actual patches ... > > RFC because the patches are essentially untested and I did not actually > try to trigger any of the things these patches are supposed to fix. It this is an interesting series, and the code makes sense, but I would really like to see some regression tests, and maybe even some selftests to trigger (at least some of) the issues. the follow-up question is: how did we manage to go on so long without noticing these issues? :D > merely matches my current understanding (and what other code does :) ). I > did compile-test as far as possible. > > After learning more about the wonderful world of page tables and their > interaction with the mmap_sem and VMAs, I spotted some issues in our > page table walkers that allow user space to trigger nasty behavior when > playing dirty tricks with munmap() or mmap() of hugetlb. While some issues > should be hard to trigger, others are fairly easy because we provide > conventient interfaces (e.g., KVM_S390_GET_SKEYS and KVM_S390_SET_SKEYS). > > Future work: > - Don't use get_locked_pte() when it's not required to actually allocate > page tables -- similar to how storage keys are now handled. Examples are > get_pgste() and __gmap_zap. > - Don't use get_locked_pte() and instead let page fault logic allocate page > tables when we actually do need page tables -- also, similar to how > storage keys are now handled. Examples are set_pgste_bits() and > pgste_perform_essa(). > - Maybe switch to mm/pagewalk.c to avoid custom page table walkers. For > __gmap_zap() that's very easy. > > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> > Cc: Janosch Frank <frankja@xxxxxxxxxxxxx> > Cc: Cornelia Huck <cohuck@xxxxxxxxxx> > Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> > Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> > Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> > Cc: Niklas Schnelle <schnelle@xxxxxxxxxxxxx> > Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx> > Cc: Ulrich Weigand <Ulrich.Weigand@xxxxxxxxxx> > > David Hildenbrand (9): > s390/gmap: validate VMA in __gmap_zap() > s390/gmap: don't unconditionally call pte_unmap_unlock() in > __gmap_zap() > s390/mm: validate VMA in PGSTE manipulation functions > s390/mm: fix VMA and page table handling code in storage key handling > functions > s390/uv: fully validate the VMA before calling follow_page() > s390/pci_mmio: fully validate the VMA before calling follow_pte() > s390/mm: no need for pte_alloc_map_lock() if we know the pmd is > present > s390/mm: optimize set_guest_storage_key() > s390/mm: optimize reset_guest_reference_bit() > > arch/s390/kernel/uv.c | 2 +- > arch/s390/mm/gmap.c | 11 +++- > arch/s390/mm/pgtable.c | 109 +++++++++++++++++++++++++++------------ > arch/s390/pci/pci_mmio.c | 4 +- > 4 files changed, 89 insertions(+), 37 deletions(-) > > > base-commit: 7d2a07b769330c34b4deabeed939325c77a7ec2f
