[PATCH 0/6] arm64: untag user pointers passed to the kernel

From: Andrey Konovalov
Date: Wed Apr 18 2018 - 14:53:29 EST


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.


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

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 âmm, arm64: untag user addresses in memory syscallsâ.
- Rebased onto 3eb2ce82 (4.16-rc7).

Andrey Konovalov (6):
arm64: add type casts to untagged_addr macro
uaccess: add untagged_addr definition for other arches
arm64: untag user addresses in copy_from_user and others
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

Documentation/arm64/tagged-pointers.txt | 5 +++--
arch/arm64/include/asm/uaccess.h | 9 +++++++--
include/linux/uaccess.h | 4 ++++
lib/strncpy_from_user.c | 2 ++
lib/strnlen_user.c | 2 ++
mm/gup.c | 12 ++++++++++++
6 files changed, 30 insertions(+), 4 deletions(-)