Hi Gwan-gyeong, On Fri, Oct 21, 2022 at 11:33:33AM +0300, Gwan-gyeong Mun wrote: > From: Kees Cook <keescook@xxxxxxxxxxxx> > > Implement a robust overflows_type() macro to test if a variable or > constant value would overflow another variable or type. This can be > used as a constant expression for static_assert() (which requires a > constant expression[1][2]) when used on constant values. This must be > constructed manually, since __builtin_add_overflow() does not produce > a constant expression[3]. > > Additionally adds castable_to_type(), similar to __same_type(), but for > checking if a constant value would overflow if cast to a given type. > > Add unit tests for overflows_type(), __same_type(), and castable_to_type() > to the existing KUnit "overflow" test. > > [1] https://en.cppreference.com/w/c/language/_Static_assert > [2] C11 standard (ISO/IEC 9899:2011): 6.7.10 Static assertions > [3] https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html > 6.56 Built-in Functions to Perform Arithmetic with Overflow Checking > Built-in Function: bool __builtin_add_overflow (type1 a, type2 b, > > Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx> > Cc: Nathan Chancellor <nathan@xxxxxxxxxx> > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Cc: Tom Rix <trix@xxxxxxxxxx> > Cc: Daniel Latypov <dlatypov@xxxxxxxxxx> > Cc: Vitor Massaru Iha <vitor@xxxxxxxxxxx> > Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx> > Cc: Jani Nikula <jani.nikula@xxxxxxxxx> > Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> > Cc: linux-hardening@xxxxxxxxxxxxxxx > Cc: llvm@xxxxxxxxxxxxxxx > Co-developed-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx> > Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> <snip> > diff --git a/lib/Makefile b/lib/Makefile > index 161d6a724ff7..e061aad90539 100644 > --- a/lib/Makefile > +++ b/lib/Makefile > @@ -376,6 +376,10 @@ obj-$(CONFIG_CMDLINE_KUNIT_TEST) += cmdline_kunit.o > obj-$(CONFIG_SLUB_KUNIT_TEST) += slub_kunit.o > obj-$(CONFIG_MEMCPY_KUNIT_TEST) += memcpy_kunit.o > obj-$(CONFIG_IS_SIGNED_TYPE_KUNIT_TEST) += is_signed_type_kunit.o > +# We're expecting to do a lot of "always true" or "always false" tests. > +ifdef CONFIG_CC_IS_CLANG > +CFLAGS_overflow_kunit.o += $(call cc-disable-warning, tautological-constant-out-of-range-compare) If you are going to wrap this in CONFIG_CC_IS_CLANG (which is good), drop the cc-disable-warning and just disable the warning directly. CFLAGS_overflow_kunit.o += -Wno-tautological-constant-out-of-range-compare All kernel supported clang versions support this warning so there is no point in checking for its existence before disabling it with cc-disable-warning. scripts/Makefile.extrawarn does this as well. > +endif > obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o > CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable) > obj-$(CONFIG_ST&ACKINIT_KUNIT_TEST) += stackinit_kunit.o Cheers, Nathan
