Re: [PATCH v19 00/15] arm64: untag user pointers passed to the kernel

[Andrey Konovalov <andreyknvl@google.com>]

On Tue, Jul 23, 2019 at 7:59 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> === Overview
>
> arm64 has a feature called Top Byte Ignore, which allows to embed pointer
> tags into the top byte of each pointer. Userspace programs (such as
> HWASan, a memory debugging tool [1]) might use this feature and pass
> tagged user pointers to the kernel through syscalls or other interfaces.
>
> Right now the kernel is already able to handle user faults with tagged
> pointers, due to these patches:
>
> 1. 81cddd65 ("arm64: traps: fix userspace cache maintenance emulation on a
>              tagged pointer")
> 2. 7dcd9dd8 ("arm64: hw_breakpoint: fix watchpoint matching for tagged
>               pointers")
> 3. 276e9327 ("arm64: entry: improve data abort handling of tagged
>               pointers")
>
> This patchset extends tagged pointer support to syscall arguments.
>
> As per the proposed ABI change [3], tagged pointers are only allowed to be
> passed to syscalls when they point to memory ranges obtained by anonymous
> mmap() or sbrk() (see the patchset [3] for more details).
>
> For non-memory syscalls this is done by untaging user pointers when the
> kernel performs pointer checking to find out whether the pointer comes
> from userspace (most notably in access_ok). The untagging is done only
> when the pointer is being checked, the tag is preserved as the pointer
> makes its way through the kernel and stays tagged when the kernel
> dereferences the pointer when perfoming user memory accesses.
>
> The mmap and mremap (only new_addr) syscalls do not currently accept
> tagged addresses. Architectures may interpret the tag as a background
> colour for the corresponding vma.
>
> Other memory syscalls (mprotect, etc.) don't do user memory accesses but
> rather deal with memory ranges, and untagged pointers are better suited to
> describe memory ranges internally. Thus for memory syscalls we untag
> pointers completely when they enter the kernel.
>
> === Other approaches
>
> One of the alternative approaches to untagging that was considered is to
> completely strip the pointer tag as the pointer enters the kernel with
> some kind of a syscall wrapper, but that won't work with the countless
> number of different ioctl calls. With this approach we would need a custom
> wrapper for each ioctl variation, which doesn't seem practical.
>
> An alternative approach to untagging pointers in memory syscalls prologues
> is to inspead allow tagged pointers to be passed to find_vma() (and other
> vma related functions) and untag them there. Unfortunately, a lot of
> find_vma() callers then compare or subtract the returned vma start and end
> fields against the pointer that was being searched. Thus this approach
> would still require changing all find_vma() callers.
>
> === Testing
>
> The following testing approaches has been taken to find potential issues
> with user pointer untagging:
>
> 1. Static testing (with sparse [2] and separately with a custom static
>    analyzer based on Clang) to track casts of __user pointers to integer
>    types to find places where untagging needs to be done.
>
> 2. Static testing with grep to find parts of the kernel that call
>    find_vma() (and other similar functions) or directly compare against
>    vm_start/vm_end fields of vma.
>
> 3. Static testing with grep to find parts of the kernel that compare
>    user pointers with TASK_SIZE or other similar consts and macros.
>
> 4. Dynamic testing: adding BUG_ON(has_tag(addr)) to find_vma() and running
>    a modified syzkaller version that passes tagged pointers to the kernel.
>
> Based on the results of the testing the requried patches have been added
> to the patchset.
>
> === Notes
>
> This patchset is meant to be merged together with "arm64 relaxed ABI" [3].
>
> This patchset is a prerequisite for ARM's memory tagging hardware feature
> support [4].
>
> This patchset has been merged into the Pixel 2 & 3 kernel trees and is
> now being used to enable testing of Pixel phones with HWASan.
>
> Thanks!
>
> [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
>
> [2] https://github.com/lucvoo/sparse-dev/commit/5f960cb10f56ec2017c128ef9d16060e0145f292
>
> [3] https://lkml.org/lkml/2019/6/12/745
>
> [4] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a

Hi Andrew and Catalin,

Do you think this is ready to be merged?

Should this go through the mm or the arm tree?

Thanks!


>
> === History
>
> Changes in v19:
> - Rebased onto 7b5cf701 (5.3-rc1+).
>
> Changes in v18:
> - Reverted the selftest back to not using the LD_PRELOAD approach.
> - Added prctl(PR_SET_TAGGED_ADDR_CTRL) call to the selftest.
> - Reworded the patch descriptions to make them less oriented on arm64
>   only.
> - Catalin's patch: "I added a Kconfig option and dropped the prctl args
>   zero check. There is some minor clean-up as well".
>
> Changes in v17:
> - The "uaccess: add noop untagged_addr definition" patch is dropped, as it
>   was merged into upstream named as "uaccess: add noop untagged_addr
>   definition".
> - Merged "mm, arm64: untag user pointers in do_pages_move" into
>   "mm, arm64: untag user pointers passed to memory syscalls".
> - Added "arm64: Introduce prctl() options to control the tagged user
>   addresses ABI" patch from Catalin.
> - Add tags_lib.so to tools/testing/selftests/arm64/.gitignore.
> - Added a comment clarifying untagged in mremap.
> - Moved untagging back into mlx4_get_umem_mr() for the IB patch.
>
> Changes in v16:
> - Moved untagging for memory syscalls from arm64 wrappers back to generic
>   code.
> - Dropped untagging for the following memory syscalls: brk, mmap, munmap;
>   mremap (only dropped for new_address); mmap_pgoff (not used on arm64);
>   remap_file_pages (deprecated); shmat, shmdt (work on shared memory).
> - Changed kselftest to LD_PRELOAD a shared library that overrides malloc
>   to return tagged pointers.
> - Rebased onto 5.2-rc3.
>
> Changes in v15:
> - Removed unnecessary untagging from radeon_ttm_tt_set_userptr().
> - Removed unnecessary untagging from amdgpu_ttm_tt_set_userptr().
> - Moved untagging to validate_range() in userfaultfd code.
> - Moved untagging to ib_uverbs_(re)reg_mr() from mlx4_get_umem_mr().
> - Rebased onto 5.1.
>
> Changes in v14:
> - Moved untagging for most memory syscalls to an arm64 specific
>   implementation, instead of doing that in the common code.
> - Dropped "net, arm64: untag user pointers in tcp_zerocopy_receive", since
>   the provided user pointers don't come from an anonymous map and thus are
>   not covered by this ABI relaxation.
> - Dropped "kernel, arm64: untag user pointers in prctl_set_mm*".
> - Moved untagging from __check_mem_type() to tee_shm_register().
> - Updated untagging for the amdgpu and radeon drivers to cover the MMU
>   notifier, as suggested by Felix.
> - Since this ABI relaxation doesn't actually allow tagged instruction
>   pointers, dropped the following patches:
> - Dropped "tracing, arm64: untag user pointers in seq_print_user_ip".
> - Dropped "uprobes, arm64: untag user pointers in find_active_uprobe".
> - Dropped "bpf, arm64: untag user pointers in stack_map_get_build_id_offset".
> - Rebased onto 5.1-rc7 (37624b58).
>
> Changes in v13:
> - Simplified untagging in tcp_zerocopy_receive().
> - Looked at find_vma() callers in drivers/, which allowed to identify a
>   few other places where untagging is needed.
> - Added patch "mm, arm64: untag user pointers in get_vaddr_frames".
> - Added patch "drm/amdgpu, arm64: untag user pointers in
>   amdgpu_ttm_tt_get_user_pages".
> - Added patch "drm/radeon, arm64: untag user pointers in
>   radeon_ttm_tt_pin_userptr".
> - Added patch "IB/mlx4, arm64: untag user pointers in mlx4_get_umem_mr".
> - Added patch "media/v4l2-core, arm64: untag user pointers in
>   videobuf_dma_contig_user_get".
> - Added patch "tee/optee, arm64: untag user pointers in check_mem_type".
> - Added patch "vfio/type1, arm64: untag user pointers".
>
> Changes in v12:
> - Changed untagging in tcp_zerocopy_receive() to also untag zc->address.
> - Fixed untagging in prctl_set_mm* to only untag pointers for vma lookups
>   and validity checks, but leave them as is for actual user space accesses.
> - Updated the link to the v2 of the "arm64 relaxed ABI" patchset [3].
> - Dropped the documentation patch, as the "arm64 relaxed ABI" patchset [3]
>   handles that.
>
> Changes in v11:
> - Added "uprobes, arm64: untag user pointers in find_active_uprobe" patch.
> - Added "bpf, arm64: untag user pointers in stack_map_get_build_id_offset"
>   patch.
> - Fixed "tracing, arm64: untag user pointers in seq_print_user_ip" to
>   correctly perform subtration with a tagged addr.
> - Moved untagged_addr() from SYSCALL_DEFINE3(mprotect) and
>   SYSCALL_DEFINE4(pkey_mprotect) to do_mprotect_pkey().
> - Moved untagged_addr() definition for other arches from
>   include/linux/memory.h to include/linux/mm.h.
> - Changed untagging in strn*_user() to perform userspace accesses through
>   tagged pointers.
> - Updated the documentation to mention that passing tagged pointers to
>   memory syscalls is allowed.
> - Updated the test to use malloc'ed memory instead of stack memory.
>
> Changes in v10:
> - Added "mm, arm64: untag user pointers passed to memory syscalls" back.
> - New patch "fs, arm64: untag user pointers in fs/userfaultfd.c".
> - New patch "net, arm64: untag user pointers in tcp_zerocopy_receive".
> - New patch "kernel, arm64: untag user pointers in prctl_set_mm*".
> - New patch "tracing, arm64: untag user pointers in seq_print_user_ip".
>
> Changes in v9:
> - Rebased onto 4.20-rc6.
> - Used u64 instead of __u64 in type casts in the untagged_addr macro for
>   arm64.
> - Added braces around (addr) in the untagged_addr macro for other arches.
>
> Changes in v8:
> - Rebased onto 65102238 (4.20-rc1).
> - Added a note to the cover letter on why syscall wrappers/shims that untag
>   user pointers won't work.
> - Added a note to the cover letter that this patchset has been merged into
>   the Pixel 2 kernel tree.
> - Documentation fixes, in particular added a list of syscalls that don't
>   support tagged user pointers.
>
> Changes in v7:
> - Rebased onto 17b57b18 (4.19-rc6).
> - Dropped the "arm64: untag user address in __do_user_fault" patch, since
>   the existing patches already handle user faults properly.
> - Dropped the "usb, arm64: untag user addresses in devio" patch, since the
>   passed pointer must come from a vma and therefore be untagged.
> - Dropped the "arm64: annotate user pointers casts detected by sparse"
>   patch (see the discussion to the replies of the v6 of this patchset).
> - Added more context to the cover letter.
> - Updated Documentation/arm64/tagged-pointers.txt.
>
> Changes in v6:
> - Added annotations for user pointer casts found by sparse.
> - Rebased onto 050cdc6c (4.19-rc1+).
>
> Changes in v5:
> - Added 3 new patches that add untagging to places found with static
>   analysis.
> - Rebased onto 44c929e1 (4.18-rc8).
>
> Changes in v4:
> - Added a selftest for checking that passing tagged pointers to the
>   kernel succeeds.
> - Rebased onto 81e97f013 (4.18-rc1+).
>
> Changes in v3:
> - Rebased onto e5c51f30 (4.17-rc6+).
> - Added linux-arch@ to the list of recipients.
>
> Changes in v2:
> - Rebased onto 2d618bdf (4.17-rc3+).
> - Removed excessive untagging in gup.c.
> - Removed untagging pointers returned from __uaccess_mask_ptr.
>
> Changes in v1:
> - Rebased onto 4.17-rc1.
>
> Changes in RFC v2:
> - Added "#ifndef untagged_addr..." fallback in linux/uaccess.h instead of
>   defining it for each arch individually.
> - Updated Documentation/arm64/tagged-pointers.txt.
> - Dropped "mm, arm64: untag user addresses in memory syscalls".
> - Rebased onto 3eb2ce82 (4.16-rc7).
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> Andrey Konovalov (14):
>   arm64: untag user pointers in access_ok and __uaccess_mask_ptr
>   lib: untag user pointers in strn*_user
>   mm: untag user pointers passed to memory syscalls
>   mm: untag user pointers in mm/gup.c
>   mm: untag user pointers in get_vaddr_frames
>   fs/namespace: untag user pointers in copy_mount_options
>   userfaultfd: untag user pointers
>   drm/amdgpu: untag user pointers
>   drm/radeon: untag user pointers in radeon_gem_userptr_ioctl
>   IB/mlx4: untag user pointers in mlx4_get_umem_mr
>   media/v4l2-core: untag user pointers in videobuf_dma_contig_user_get
>   tee/shm: untag user pointers in tee_shm_register
>   vfio/type1: untag user pointers in vaddr_get_pfn
>   selftests, arm64: add a selftest for passing tagged pointers to kernel
>
> Catalin Marinas (1):
>   arm64: Introduce prctl() options to control the tagged user addresses
>     ABI
>
>  arch/arm64/Kconfig                            |  9 +++
>  arch/arm64/include/asm/processor.h            |  8 ++
>  arch/arm64/include/asm/thread_info.h          |  1 +
>  arch/arm64/include/asm/uaccess.h              | 12 ++-
>  arch/arm64/kernel/process.c                   | 73 +++++++++++++++++++
>  .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c  |  2 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c       |  2 +
>  drivers/gpu/drm/radeon/radeon_gem.c           |  2 +
>  drivers/infiniband/hw/mlx4/mr.c               |  7 +-
>  drivers/media/v4l2-core/videobuf-dma-contig.c |  9 ++-
>  drivers/tee/tee_shm.c                         |  1 +
>  drivers/vfio/vfio_iommu_type1.c               |  2 +
>  fs/namespace.c                                |  2 +-
>  fs/userfaultfd.c                              | 22 +++---
>  include/uapi/linux/prctl.h                    |  5 ++
>  kernel/sys.c                                  | 12 +++
>  lib/strncpy_from_user.c                       |  3 +-
>  lib/strnlen_user.c                            |  3 +-
>  mm/frame_vector.c                             |  2 +
>  mm/gup.c                                      |  4 +
>  mm/madvise.c                                  |  2 +
>  mm/mempolicy.c                                |  3 +
>  mm/migrate.c                                  |  2 +-
>  mm/mincore.c                                  |  2 +
>  mm/mlock.c                                    |  4 +
>  mm/mprotect.c                                 |  2 +
>  mm/mremap.c                                   |  7 ++
>  mm/msync.c                                    |  2 +
>  tools/testing/selftests/arm64/.gitignore      |  1 +
>  tools/testing/selftests/arm64/Makefile        | 11 +++
>  .../testing/selftests/arm64/run_tags_test.sh  | 12 +++
>  tools/testing/selftests/arm64/tags_test.c     | 29 ++++++++
>  32 files changed, 233 insertions(+), 25 deletions(-)
>  create mode 100644 tools/testing/selftests/arm64/.gitignore
>  create mode 100644 tools/testing/selftests/arm64/Makefile
>  create mode 100755 tools/testing/selftests/arm64/run_tags_test.sh
>  create mode 100644 tools/testing/selftests/arm64/tags_test.c
>
> --
> 2.22.0.709.g102302147b-goog
>