On Thu, Aug 13, 2020 at 08:39:44AM +0200, Rasmus Villemoes wrote: > On 12/08/2020 23.51, Kees Cook wrote: > > Since the destination variable of the check_*_overflow() helpers will > > contain a wrapped value on failure, it would be best to make sure callers > > really did check the return result of the helper. Adjust the macros to use > > a bool-wrapping static inline that is marked with __must_check. This means > > the macros can continue to have their type-agnostic behavior while gaining > > the function attribute (that cannot be applied directly to macros). > > > > Suggested-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > include/linux/overflow.h | 51 +++++++++++++++++++++++----------------- > > 1 file changed, 30 insertions(+), 21 deletions(-) > > > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > > index 93fcef105061..ef7d538c2d08 100644 > > --- a/include/linux/overflow.h > > +++ b/include/linux/overflow.h > > @@ -43,6 +43,16 @@ > > #define is_non_negative(a) ((a) > 0 || (a) == 0) > > #define is_negative(a) (!(is_non_negative(a))) > > > > +/* > > + * Allows to effectively us apply __must_check to a macro so we can have > > word ordering? This and the __must_check-bool() renaming now done and sent in v2. Thanks! > Sorry, I meant to send this before your cooking was done but forgot > about it again. Not a big deal, but it occurred to me it might be better > to rename the existing check_*_overflow to __check_*_overflow (in both > branches of the COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW), and then > > #define check_*_overflow(a, b, d) > __must_check_bool(__check_*_overflow(a, b, d)) At the end of the day, I'd rather not have a way to ignore the overflow in this way -- I'd rather have a set of wrap_mul_overflow() helpers instead. Then we've got proper annotation of the expectation (and a place for function attributes to be added to tell sanitizers to ignore overflow). -- Kees Cook
