[PATCH v5 00/10] arm64: untag user pointers passed to the kernel

[Andrey Konovalov]

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.

This patch makes a few of the kernel interfaces accept tagged user
pointers. The kernel is already able to handle user faults with tagged
pointers and has the untagged_addr macro, which this patchset reuses.

Thanks!

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

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).

Andrey Konovalov (10):
  arm64: add type casts to untagged_addr macro
  uaccess: add untagged_addr definition for other arches
  arm64: untag user addresses in access_ok and __uaccess_mask_ptr
  mm, arm64: untag user addresses in mm/gup.c
  lib, arm64: untag addrs passed to strncpy_from_user and strnlen_user
  arm64: untag user address in __do_user_fault
  fs, arm64: untag user address in copy_mount_options
  usb, arm64: untag user addresses in devio
  arm64: update Documentation/arm64/tagged-pointers.txt
  selftests, arm64: add a selftest for passing tagged pointers to kernel

 Documentation/arm64/tagged-pointers.txt       |  5 +++--
 arch/arm64/include/asm/uaccess.h              | 14 +++++++++-----
 arch/arm64/mm/fault.c                         |  2 +-
 drivers/usb/core/devio.c                      |  8 +++++---
 fs/namespace.c                                |  2 +-
 include/linux/uaccess.h                       |  4 ++++
 lib/strncpy_from_user.c                       |  2 ++
 lib/strnlen_user.c                            |  2 ++
 mm/gup.c                                      |  4 ++++
 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     | 19 +++++++++++++++++++
 13 files changed, 74 insertions(+), 12 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

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2.18.0.597.ga71716f1ad-goog