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 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 (6): 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 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 ++++ 6 files changed, 24 insertions(+), 7 deletions(-) -- 2.17.0.921.gf22659ad46-goog
