Messages in this thread | | | Subject | Re: [PATCH resend RFC 0/9] s390: fixes, cleanups and optimizations for page table walkers | From | David Hildenbrand <> | Date | Tue, 14 Sep 2021 20:06:17 +0200 |
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On 14.09.21 18:50, Claudio Imbrenda wrote: > On Thu, 9 Sep 2021 18:22:39 +0200 > David Hildenbrand <david@redhat.com> 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.
Yep, it most certainly needs regression testing before picking any of this. selftests would be great, but I won't find time for it in the foreseeable future.
> > the follow-up question is: how did we manage to go on so long without > noticing these issues? :D
Excellent question - I guess we simply weren't aware of the dos and don'ts when dealing with process page tables :)
> >> 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@de.ibm.com> >> Cc: Janosch Frank <frankja@linux.ibm.com> >> Cc: Cornelia Huck <cohuck@redhat.com> >> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> >> Cc: Heiko Carstens <hca@linux.ibm.com> >> Cc: Vasily Gorbik <gor@linux.ibm.com> >> Cc: Niklas Schnelle <schnelle@linux.ibm.com> >> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> >> Cc: Ulrich Weigand <Ulrich.Weigand@de.ibm.com> >> >> 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 >
-- Thanks,
David / dhildenb
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