Re: [PATCH v6 13/41] mm: Make pte_mkwrite() take a VMA

[David Hildenbrand <david@redhat.com>]

On 18.02.23 22:14, Rick Edgecombe wrote:
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
> 
> One of these unusual properties is that shadow stack memory is writable,
> but only in limited ways. These limits are applied via a specific PTE
> bit combination. Nevertheless, the memory is writable, and core mm code
> will need to apply the writable permissions in the typical paths that
> call pte_mkwrite().
> 
> In addition to VM_WRITE, the shadow stack VMA's will have a flag denoting
> that they are special shadow stack flavor of writable memory. So make
> pte_mkwrite() take a VMA, so that the x86 implementation of it can know to
> create regular writable memory or shadow stack memory.
> 
> Apply the same changes for pmd_mkwrite() and huge_pte_mkwrite().
> 
> No functional change.
> 
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-alpha@vger.kernel.org
> Cc: linux-snps-arc@lists.infradead.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-csky@vger.kernel.org
> Cc: linux-hexagon@vger.kernel.org
> Cc: linux-ia64@vger.kernel.org
> Cc: loongarch@lists.linux.dev
> Cc: linux-m68k@lists.linux-m68k.org
> Cc: Michal Simek <monstr@monstr.eu>
> Cc: Dinh Nguyen <dinguyen@kernel.org>
> Cc: linux-mips@vger.kernel.org
> Cc: openrisc@lists.librecores.org
> Cc: linux-parisc@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-riscv@lists.infradead.org
> Cc: linux-s390@vger.kernel.org
> Cc: linux-sh@vger.kernel.org
> Cc: sparclinux@vger.kernel.org
> Cc: linux-um@lists.infradead.org
> Cc: xen-devel@lists.xenproject.org
> Cc: linux-arch@vger.kernel.org
> Cc: linux-mm@kvack.org
> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> 
> ---
> Hi Non-x86 Arch’s,
> 
> x86 has a feature that allows for the creation of a special type of
> writable memory (shadow stack) that is only writable in limited specific
> ways. Previously, changes were proposed to core MM code to teach it to
> decide when to create normally writable memory or the special shadow stack
> writable memory, but David Hildenbrand suggested[0] to change
> pXX_mkwrite() to take a VMA, so awareness of shadow stack memory can be
> moved into x86 code.
> 
> Since pXX_mkwrite() is defined in every arch, it requires some tree-wide
> changes. So that is why you are seeing some patches out of a big x86
> series pop up in your arch mailing list. There is no functional change.
> After this refactor, the shadow stack series goes on to use the arch
> helpers to push shadow stack memory details inside arch/x86.
> 
> Testing was just 0-day build testing.
> 
> Hopefully that is enough context. Thanks!
> 
> [0] https://lore.kernel.org/lkml/0e29a2d0-08d8-bcd6-ff26-4bea0e4037b0@redhat.com/#t
> 
> v6:
>   - New patch
> ---
>   Documentation/mm/arch_pgtable_helpers.rst    |  9 ++++++---
>   arch/alpha/include/asm/pgtable.h             |  6 +++++-
>   arch/arc/include/asm/hugepage.h              |  2 +-
>   arch/arc/include/asm/pgtable-bits-arcv2.h    |  7 ++++++-
>   arch/arm/include/asm/pgtable-3level.h        |  7 ++++++-
>   arch/arm/include/asm/pgtable.h               |  2 +-
>   arch/arm64/include/asm/pgtable.h             |  4 ++--
>   arch/csky/include/asm/pgtable.h              |  2 +-
>   arch/hexagon/include/asm/pgtable.h           |  2 +-
>   arch/ia64/include/asm/pgtable.h              |  2 +-
>   arch/loongarch/include/asm/pgtable.h         |  4 ++--
>   arch/m68k/include/asm/mcf_pgtable.h          |  2 +-
>   arch/m68k/include/asm/motorola_pgtable.h     |  6 +++++-
>   arch/m68k/include/asm/sun3_pgtable.h         |  6 +++++-
>   arch/microblaze/include/asm/pgtable.h        |  2 +-
>   arch/mips/include/asm/pgtable.h              |  6 +++---
>   arch/nios2/include/asm/pgtable.h             |  2 +-
>   arch/openrisc/include/asm/pgtable.h          |  2 +-
>   arch/parisc/include/asm/pgtable.h            |  6 +++++-
>   arch/powerpc/include/asm/book3s/32/pgtable.h |  2 +-
>   arch/powerpc/include/asm/book3s/64/pgtable.h |  4 ++--
>   arch/powerpc/include/asm/nohash/32/pgtable.h |  2 +-
>   arch/powerpc/include/asm/nohash/32/pte-8xx.h |  2 +-
>   arch/powerpc/include/asm/nohash/64/pgtable.h |  2 +-
>   arch/riscv/include/asm/pgtable.h             |  6 +++---
>   arch/s390/include/asm/hugetlb.h              |  4 ++--
>   arch/s390/include/asm/pgtable.h              |  4 ++--
>   arch/sh/include/asm/pgtable_32.h             | 10 ++++++++--
>   arch/sparc/include/asm/pgtable_32.h          |  2 +-
>   arch/sparc/include/asm/pgtable_64.h          |  6 +++---
>   arch/um/include/asm/pgtable.h                |  2 +-
>   arch/x86/include/asm/pgtable.h               |  6 ++++--
>   arch/xtensa/include/asm/pgtable.h            |  2 +-
>   include/asm-generic/hugetlb.h                |  4 ++--
>   include/linux/mm.h                           |  2 +-
>   mm/debug_vm_pgtable.c                        | 16 ++++++++--------
>   mm/huge_memory.c                             |  6 +++---
>   mm/hugetlb.c                                 |  4 ++--
>   mm/memory.c                                  |  4 ++--
>   mm/migrate_device.c                          |  2 +-
>   mm/mprotect.c                                |  2 +-
>   mm/userfaultfd.c                             |  2 +-
>   42 files changed, 106 insertions(+), 69 deletions(-)

That looks painful but IMHO worth it :)

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb


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