On Mon, Jan 29, 2024 at 09:08:43PM +0100, Rasmus Villemoes wrote: > On 29/01/2024 19.34, Kees Cook wrote: > > Provide helpers that will perform wrapping addition, subtraction, or > > multiplication without tripping the arithmetic wrap-around sanitizers. The > > first argument is the type under which the wrap-around should happen > > with. In other words, these two calls will get very different results: > > > > add_wrap(int, 50, 50) == 2500 > > add_wrap(u8, 50, 50) == 196 > > s/add/mul/g I suppose.
Oops, yes. > > Cc: Rasmus Villemoes <rasmus.villem...@prevas.dk> > > Cc: Mark Rutland <mark.rutl...@arm.com> > > Cc: linux-hardening@vger.kernel.org > > Signed-off-by: Kees Cook <keesc...@chromium.org> > > --- > > include/linux/overflow.h | 54 ++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 54 insertions(+) > > > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > > index 3c46c648d2e8..4f945e9e7881 100644 > > --- a/include/linux/overflow.h > > +++ b/include/linux/overflow.h > > @@ -120,6 +120,24 @@ static inline bool __must_check > > __must_check_overflow(bool overflow) > > check_add_overflow(var, offset, &__result); \ > > })) > > > > +/** > > + * add_wrap() - Intentionally perform a wrapping addition > > + * @type: type to check overflow against > > Well, nothing is "checked", so why not just say "type of result"? Yeah, that's better. I was trying to describe that @type will affect the value of the result. > > +/** > > + * sub_wrap() - Intentionally perform a wrapping subtraction > > + * @type: type to check underflow against > > The terminology becomes muddy, is (INT_MAX) - (-1) an underflow or > overflow? Anyway, see above. Right, I should explicitly say "wrap-around". > > > > > +/** > > + * mul_wrap() - Intentionally perform a wrapping multiplication > > + * @type: type to check underflow against > > And here there's definitely a copy-pasto. Ek, yes. > The code itself looks fine. Thanks! -- Kees Cook
