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Subject[PATCH v4 0/7] arm64: untag user pointers passed to the kernel
Date
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.

We're not trying to cover all possible ways the kernel accepts user
pointers in one patchset, so this one should be considered as a start.

Thanks!

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

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 (7):
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: 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 +++++++++-----
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 +++++++++++++++++++
10 files changed, 67 insertions(+), 7 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

--
2.18.0.rc1.244.gcf134e6275-goog

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