From: Kees Cook keescook@chromium.org
When the check_[op]_overflow() helpers were introduced, all arguments were required to be the same type to make the fallback macros simpler. However, now that the fallback macros have been removed[1], it is fine to allow mixed types, which makes using the helpers much more useful, as they can be used to test for type-based overflows (e.g. adding two large ints but storing into a u8), as would be handy in the drm core[2].
Remove the restriction, and add additional self-tests that exercise some of the mixed-type overflow cases, and double-check for accidental macro side-effects.
[1] https://git.kernel.org/linus/4eb6bd55cfb22ffc20652732340c4962f3ac9a91 [2] https://lore.kernel.org/lkml/20220824084514.2261614-2-gwan-gyeong.mun@intel....
Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Cc: Gwan-gyeong Mun gwan-gyeong.mun@intel.com Cc: "Gustavo A. R. Silva" gustavoars@kernel.org Cc: Nick Desaulniers ndesaulniers@google.com Cc: linux-hardening@vger.kernel.org Reviewed-by: Andrzej Hajda andrzej.hajda@intel.com Reviewed-by: Gwan-gyeong Mun gwan-gyeong.mun@intel.com Tested-by: Gwan-gyeong Mun gwan-gyeong.mun@intel.com Signed-off-by: Kees Cook keescook@chromium.org [florian: Drop changes to lib/test_overflow.c] Signed-off-by: Florian Fainelli florian.fainelli@broadcom.com --- include/linux/overflow.h | 72 +++++++++++++++++++++++----------------- 1 file changed, 41 insertions(+), 31 deletions(-)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h index d1dd039fe1c3..54788a3cdcf5 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -55,40 +55,50 @@ static inline bool __must_check __must_check_overflow(bool overflow) }
#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW -/* - * For simplicity and code hygiene, the fallback code below insists on - * a, b and *d having the same type (similar to the min() and max() - * macros), whereas gcc's type-generic overflow checkers accept - * different types. Hence we don't just make check_add_overflow an - * alias for __builtin_add_overflow, but add type checks similar to - * below. +/** check_add_overflow() - Calculate addition with overflow checking + * + * @a: first addend + * @b: second addend + * @d: pointer to store sum + * + * Returns 0 on success. + * + * *@d holds the results of the attempted addition, but is not considered + * "safe for use" on a non-zero return value, which indicates that the + * sum has overflowed or been truncated. */ -#define check_add_overflow(a, b, d) __must_check_overflow(({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - __builtin_add_overflow(__a, __b, __d); \ -})) +#define check_add_overflow(a, b, d) \ + __must_check_overflow(__builtin_add_overflow(a, b, d))
-#define check_sub_overflow(a, b, d) __must_check_overflow(({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - __builtin_sub_overflow(__a, __b, __d); \ -})) +/** check_sub_overflow() - Calculate subtraction with overflow checking + * + * @a: minuend; value to subtract from + * @b: subtrahend; value to subtract from @a + * @d: pointer to store difference + * + * Returns 0 on success. + * + * *@d holds the results of the attempted subtraction, but is not considered + * "safe for use" on a non-zero return value, which indicates that the + * difference has underflowed or been truncated. + */ +#define check_sub_overflow(a, b, d) \ + __must_check_overflow(__builtin_sub_overflow(a, b, d))
-#define check_mul_overflow(a, b, d) __must_check_overflow(({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - __builtin_mul_overflow(__a, __b, __d); \ -})) +/** check_mul_overflow() - Calculate multiplication with overflow checking + * + * @a: first factor + * @b: second factor + * @d: pointer to store product + * + * Returns 0 on success. + * + * *@d holds the results of the attempted multiplication, but is not + * considered "safe for use" on a non-zero return value, which indicates + * that the product has overflowed or been truncated. + */ +#define check_mul_overflow(a, b, d) \ + __must_check_overflow(__builtin_mul_overflow(a, b, d))
#else