Linux kernel stable tree (mirror) https://git.radix-linux.su/kernel/linux.git/atom?h=v6.18.21 2025-09-08T21:58:52+00:00 2025-09-08T21:58:52+00:00 Kees Cook kees@kernel.org 2025-08-04T16:44:13+00:00 urn:sha1:95719dfa323709c06ec34cc96e73e0788e19934f While tracking down a problem where constant expressions used by BUILD_BUG_ON() suddenly stopped working[1], we found that an added static initializer was convincing the compiler that it couldn't track the state of the prior statically initialized value. Tracing this down found that ffs() was used in the initializer macro, but since it wasn't marked with __attribute_const__, the compiler had to assume the function might change variable states as a side-effect (which is not true for ffs(), which provides deterministic math results). Validate all the __attibute_const__ annotations were found for all architectures by reproducing the specific problem encountered in the original bug report. Build and run tested with everything I could reach with KUnit: $ ./tools/testing/kunit/kunit.py run --arch=x86_64 ffs $ ./tools/testing/kunit/kunit.py run --arch=i386 ffs $ ./tools/testing/kunit/kunit.py run --arch=arm64 --make_options "CROSS_COMPILE=aarch64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=arm --make_options "CROSS_COMPILE=arm-linux-gnueabi-" ffs $ ./tools/testing/kunit/kunit.py run --arch=powerpc ffs $ ./tools/testing/kunit/kunit.py run --arch=powerpc32 ffs $ ./tools/testing/kunit/kunit.py run --arch=powerpcle ffs $ ./tools/testing/kunit/kunit.py run --arch=m68k ffs $ ./tools/testing/kunit/kunit.py run --arch=loongarch ffs $ ./tools/testing/kunit/kunit.py run --arch=s390 --make_options "CROSS_COMPILE=s390x-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=riscv --make_options "CROSS_COMPILE=riscv64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=riscv32 --make_options "CROSS_COMPILE=riscv64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=sparc --make_options "CROSS_COMPILE=sparc64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=sparc64 --make_options "CROSS_COMPILE=sparc64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=alpha --make_options "CROSS_COMPILE=alpha-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=sh --make_options "CROSS_COMPILE=sh4-linux-gnu-" ffs Closes: https://github.com/KSPP/linux/issues/364 Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250804164417.1612371-17-kees@kernel.org Signed-off-by: Kees Cook <kees@kernel.org> 2025-09-08T21:58:50+00:00 Kees Cook kees@kernel.org 2025-08-04T16:43:57+00:00 urn:sha1:b3a7bb71bfcd56c8266af8cf2a5dee3802e7a449 Add KUnit tests for ffs()-family bit scanning functions: ffs(), __ffs(), fls(), __fls(), fls64(), __ffs64(), and ffz(). The tests validate mathematical relationships (e.g. ffs(x) == __ffs(x) + 1), and test zero values, power-of-2 patterns, maximum values, and sparse bit patterns. Build and run tested with everything I could reach with KUnit: $ ./tools/testing/kunit/kunit.py run --arch=x86_64 ffs $ ./tools/testing/kunit/kunit.py run --arch=i386 ffs $ ./tools/testing/kunit/kunit.py run --arch=arm64 --make_options "CROSS_COMPILE=aarch64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=arm --make_options "CROSS_COMPILE=arm-linux-gnueabihf-" ffs $ ./tools/testing/kunit/kunit.py run --arch=powerpc ffs $ ./tools/testing/kunit/kunit.py run --arch=powerpc32 ffs $ ./tools/testing/kunit/kunit.py run --arch=powerpcle ffs $ ./tools/testing/kunit/kunit.py run --arch=riscv --make_options "CROSS_COMPILE=riscv64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=riscv32 --make_options "CROSS_COMPILE=riscv64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=s390 --make_options "CROSS_COMPILE=s390x-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=m68k ffs $ ./tools/testing/kunit/kunit.py run --arch=loongarch ffs $ ./tools/testing/kunit/kunit.py run --arch=mips --make_options "CROSS_COMPILE=mipsel-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=sparc --make_options "CROSS_COMPILE=sparc64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=sparc64 --make_options "CROSS_COMPILE=sparc64-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=alpha --make_options "CROSS_COMPILE=alpha-linux-gnu-" ffs $ ./tools/testing/kunit/kunit.py run --arch=sh --make_options "CROSS_COMPILE=sh4-linux-gnu-" ffs Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250804164417.1612371-1-kees@kernel.org Signed-off-by: Kees Cook <kees@kernel.org>