| Message ID | 20240206103201.2013060-2-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | overflow: Introduce wrapping helpers | expand |
On 2/6/24 04:31, 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: > > wrapping_mul(int, 50, 50) == 2500 > wrapping_mul(u8, 50, 50) == 196 > > Add to the selftests to validate behavior and lack of side-effects. > > Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk> > Cc: Marco Elver <elver@google.com> > Cc: Eric Biggers <ebiggers@kernel.org> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: linux-hardening@vger.kernel.org > Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > include/linux/overflow.h | 54 ++++++++++++++++++++++++++++++++++++++++ > lib/overflow_kunit.c | 24 +++++++++++++++--- > 2 files changed, 74 insertions(+), 4 deletions(-) > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index 4e741ebb8005..429c4d61a940 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -64,6 +64,24 @@ static inline bool __must_check __must_check_overflow(bool overflow) > #define check_add_overflow(a, b, d) \ > __must_check_overflow(__builtin_add_overflow(a, b, d)) > > +/** > + * wrapping_add() - Intentionally perform a wrapping addition > + * @type: type for result of calculation > + * @a: first addend > + * @b: second addend > + * > + * Return the potentially wrapped-around addition without > + * tripping any wrap-around sanitizers that may be enabled. > + */ > +#define wrapping_add(type, a, b) \ > + ({ \ > + type __val; \ > + if (__builtin_add_overflow(a, b, &__val)) { \ > + /* do nothing */ \ > + } \ > + __val; \ mmh... now that __builtin_*_overflow() is directly used, I guess we don't need to _check_ for overflow anymore. Thanks -- Gustavo
On Tue, Feb 06, 2024 at 10:54:06AM -0600, Gustavo A. R. Silva wrote: > > > On 2/6/24 04:31, 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: > > > > wrapping_mul(int, 50, 50) == 2500 > > wrapping_mul(u8, 50, 50) == 196 > > > > Add to the selftests to validate behavior and lack of side-effects. > > > > Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk> > > Cc: Marco Elver <elver@google.com> > > Cc: Eric Biggers <ebiggers@kernel.org> > > Cc: Mark Rutland <mark.rutland@arm.com> > > Cc: linux-hardening@vger.kernel.org > > Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org> > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > include/linux/overflow.h | 54 ++++++++++++++++++++++++++++++++++++++++ > > lib/overflow_kunit.c | 24 +++++++++++++++--- > > 2 files changed, 74 insertions(+), 4 deletions(-) > > > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > > index 4e741ebb8005..429c4d61a940 100644 > > --- a/include/linux/overflow.h > > +++ b/include/linux/overflow.h > > @@ -64,6 +64,24 @@ static inline bool __must_check __must_check_overflow(bool overflow) > > #define check_add_overflow(a, b, d) \ > > __must_check_overflow(__builtin_add_overflow(a, b, d)) > > +/** > > + * wrapping_add() - Intentionally perform a wrapping addition > > + * @type: type for result of calculation > > + * @a: first addend > > + * @b: second addend > > + * > > + * Return the potentially wrapped-around addition without > > + * tripping any wrap-around sanitizers that may be enabled. > > + */ > > +#define wrapping_add(type, a, b) \ > > + ({ \ > > + type __val; \ > > + if (__builtin_add_overflow(a, b, &__val)) { \ > > + /* do nothing */ \ > > + } \ > > + __val; \ > > mmh... now that __builtin_*_overflow() is directly used, I guess > we don't need to _check_ for overflow anymore. /me slaps his forehead Yes indeed! I will adjust it.
diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 4e741ebb8005..429c4d61a940 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -64,6 +64,24 @@ static inline bool __must_check __must_check_overflow(bool overflow) #define check_add_overflow(a, b, d) \ __must_check_overflow(__builtin_add_overflow(a, b, d)) +/** + * wrapping_add() - Intentionally perform a wrapping addition + * @type: type for result of calculation + * @a: first addend + * @b: second addend + * + * Return the potentially wrapped-around addition without + * tripping any wrap-around sanitizers that may be enabled. + */ +#define wrapping_add(type, a, b) \ + ({ \ + type __val; \ + if (__builtin_add_overflow(a, b, &__val)) { \ + /* do nothing */ \ + } \ + __val; \ + }) + /** * check_sub_overflow() - Calculate subtraction with overflow checking * @a: minuend; value to subtract from @@ -77,6 +95,24 @@ static inline bool __must_check __must_check_overflow(bool overflow) #define check_sub_overflow(a, b, d) \ __must_check_overflow(__builtin_sub_overflow(a, b, d)) +/** + * wrapping_sub() - Intentionally perform a wrapping subtraction + * @type: type for result of calculation + * @a: minuend; value to subtract from + * @b: subtrahend; value to subtract from @a + * + * Return the potentially wrapped-around subtraction without + * tripping any wrap-around sanitizers that may be enabled. + */ +#define wrapping_sub(type, a, b) \ + ({ \ + type __val; \ + if (__builtin_sub_overflow(a, b, &__val)) { \ + /* do nothing */ \ + } \ + __val; \ + }) + /** * check_mul_overflow() - Calculate multiplication with overflow checking * @a: first factor @@ -90,6 +126,24 @@ static inline bool __must_check __must_check_overflow(bool overflow) #define check_mul_overflow(a, b, d) \ __must_check_overflow(__builtin_mul_overflow(a, b, d)) +/** + * wrapping_mul() - Intentionally perform a wrapping multiplication + * @type: type for result of calculation + * @a: first factor + * @b: second factor + * + * Return the potentially wrapped-around multiplication without + * tripping any wrap-around sanitizers that may be enabled. + */ +#define wrapping_mul(type, a, b) \ + ({ \ + type __val; \ + if (__builtin_mul_overflow(a, b, &__val)) { \ + /* do nothing */ \ + } \ + __val; \ + }) + /** * check_shl_overflow() - Calculate a left-shifted value and check overflow * @a: Value to be shifted diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index c527f6b75789..d3fdb906d3fe 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -258,20 +258,36 @@ DEFINE_TEST_ARRAY(s64) = { \ _of = check_ ## op ## _overflow(a, b, &_r); \ KUNIT_EXPECT_EQ_MSG(test, _of, of, \ - "expected "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ + "expected check "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ a, b, of ? "" : " not", #t); \ KUNIT_EXPECT_EQ_MSG(test, _r, r, \ - "expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ + "expected check "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ a, b, r, _r, #t); \ /* Check for internal macro side-effects. */ \ _of = check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \ - KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, "Unexpected " #op " macro side-effect!\n"); \ - KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, "Unexpected " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \ + "Unexpected check " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ + "Unexpected check " #op " macro side-effect!\n"); \ + \ + _r = wrapping_ ## op(t, a, b); \ + KUNIT_EXPECT_TRUE_MSG(test, _r == r, \ + "expected wrap "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ + a, b, r, _r, #t); \ + /* Check for internal macro side-effects. */ \ + _a_orig = a; \ + _b_orig = b; \ + _r = wrapping_ ## op(t, _a_orig++, _b_orig++); \ + KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \ + "Unexpected wrap " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ + "Unexpected wrap " #op " macro side-effect!\n"); \ } while (0) #define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \ static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \ { \ + /* check_{add,sub,mul}_overflow() and wrapping_{add,sub,mul} */ \ check_one_op(t, fmt, add, "+", p->a, p->b, p->sum, p->s_of); \ check_one_op(t, fmt, add, "+", p->b, p->a, p->sum, p->s_of); \ check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of); \