| Message ID | 20240213221100.3556356-1-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Commit | afbc0e53c5a0aa8d248a48111562a715c30678f2 |
| Headers | show |
| Series | overflow: Introduce wrapping helpers | expand |
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 <gustavoars@kernel.org> > Cc: linux-hardening@vger.kernel.org > Signed-off-by: Kees Cook <keescook@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 >
On Wed, Feb 14, 2024 at 11:57:28AM +0000, Mark Rutland wrote: > 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 <gustavoars@kernel.org> > > Cc: linux-hardening@vger.kernel.org > > Signed-off-by: Kees Cook <keescook@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). Yeah, that's a good point. I'll update this. > > * > > - * *@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? Yeah, that's more clear. Thanks! -Kees
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. * - * *@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. */ #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))