On Tue, Feb 13, 2024 at 02:10:57PM -0800, Kees Cook wrote: > The check_*_overflow() helpers will return results with potentially > wrapped-around values. These values have always been checked by the > selftests, so avoid the confusing language in the kern-doc. The idea of > "safe for use" was relative to the expectation of whether or not the > caller wants a wrapped value -- the calculation itself will always follow > arithmetic wrapping rules. > > Reviewed-by: Gustavo A. R. Silva <gustavo...@kernel.org> > Cc: linux-hardening@vger.kernel.org > Signed-off-by: Kees Cook <keesc...@chromium.org> > --- > include/linux/overflow.h | 18 ++++++------------ > 1 file changed, 6 insertions(+), 12 deletions(-) > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index 7b5cf4a5cd19..4e741ebb8005 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -57,11 +57,9 @@ static inline bool __must_check __must_check_overflow(bool > overflow) > * @b: second addend > * @d: pointer to store sum > * > - * Returns 0 on success. > + * Returns 0 on success, 1 on wrap-around.
Sorry for the last minute bikeshedding, but could we clarify 'success' here? e.g. I think it'd be clearer to say: Returns true on wrap-around, false otherwise. Note that also uses true/false since these all return bool (as do the underlying __builtin_*_overflow() functions). > * > - * *@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. > + * *@d holds the results of the attempted addition, which may wrap-around. How about: @d holds the results of the attempted addition, regardless of whether wrap-around occurred. ... and likewise for the others below? Mark. > */ > #define check_add_overflow(a, b, d) \ > __must_check_overflow(__builtin_add_overflow(a, b, d)) > @@ -72,11 +70,9 @@ static inline bool __must_check __must_check_overflow(bool > overflow) > * @b: subtrahend; value to subtract from @a > * @d: pointer to store difference > * > - * Returns 0 on success. > + * Returns 0 on success, 1 on wrap-around. > * > - * *@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. > + * *@d holds the results of the attempted subtraction, which may wrap-around. > */ > #define check_sub_overflow(a, b, d) \ > __must_check_overflow(__builtin_sub_overflow(a, b, d)) > @@ -87,11 +83,9 @@ static inline bool __must_check __must_check_overflow(bool > overflow) > * @b: second factor > * @d: pointer to store product > * > - * Returns 0 on success. > + * Returns 0 on success, 1 on wrap-around. > * > - * *@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. > + * *@d holds the results of the attempted multiplication, which may > wrap-around. > */ > #define check_mul_overflow(a, b, d) \ > __must_check_overflow(__builtin_mul_overflow(a, b, d)) > -- > 2.34.1 >
