[0/3] Fix FORTIFY=y UBSAN_LOCAL_BOUNDS=y

Message

Nick Desaulniers Aug. 30, 2022, 8:53 p.m. UTC

With CONFIG_FORTIFY=y and CONFIG_UBSAN_LOCAL_BOUNDS=y enabled, we
observe a runtime panic while running Android's Compatibility Test
Suite's (CTS) android.hardware.input.cts.tests.  This is stemming from a
strlen() call in hidinput_allocate().

__builtin_object_size(str, 0 or 1) has interesting behavior for C
strings when str is runtime dependent, and all possible values are known
at compile time; it evaluates to the maximum of those sizes. This causes
UBSAN_LOCAL_BOUNDS to insert faults for the smaller values, which we
trip at runtime.

Patch 1 adds a KCONFIG version check for __builtin_dynamic_object_size,
and uses that in __compiletime_strlen rather than __builtin_object_size.
Patch 2 and 3 are cosmetic cleanups, they're not as important to me as
patch 1 is.

Nick Desaulniers (3):
  fortify: use __builtin_dynamic_object_size in __compiletime_strlen
  fortify: cosmetic cleanups to __compiletime_strlen
  HID: avoid runtime call to strlen

 drivers/hid/hid-input.c        | 13 ++++++++++++-
 include/linux/fortify-string.h | 15 ++++++++++-----
 init/Kconfig                   |  3 +++
 3 files changed, 25 insertions(+), 6 deletions(-)