On Wed, Feb 14, 2024 at 11:46:03AM -0800, Kees Cook wrote: > This allows replacements of the idioms "var += offset" and "var -= > offset" with the wrapping_assign_add() and wrapping_assign_sub() helpers > respectively. They will avoid wrap-around sanitizer instrumentation. > > Add to the selftests to validate behavior and lack of side-effects. > > Signed-off-by: Kees Cook <[email protected]> > --- > Cc: Rasmus Villemoes <[email protected]> > Cc: Marco Elver <[email protected]> > Cc: Eric Biggers <[email protected]> > Cc: Mark Rutland <[email protected]> > Cc: "Gustavo A. R. Silva" <[email protected]> > Cc: [email protected]
Acked-by: Mark Rutland <[email protected]> Mark. > --- > include/linux/overflow.h | 32 ++++++++++++++++++++++++++++++ > lib/overflow_kunit.c | 43 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 75 insertions(+) > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index d3ff8e2bec29..dede374832c9 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -81,6 +81,22 @@ static inline bool __must_check __must_check_overflow(bool > overflow) > __val; \ > }) > > +/** > + * wrapping_assign_add() - Intentionally perform a wrapping increment > assignment > + * @var: variable to be incremented > + * @offset: amount to add > + * > + * Increments @var by @offset with wrap-around. Returns the resulting > + * value of @var. Will not trip any wrap-around sanitizers. > + * > + * Returns the new value of @var. > + */ > +#define wrapping_assign_add(var, offset) \ > + ({ \ > + typeof(var) *__ptr = &(var); \ > + *__ptr = wrapping_add(typeof(var), *__ptr, offset); \ > + }) > + > /** > * check_sub_overflow() - Calculate subtraction with overflow checking > * @a: minuend; value to subtract from > @@ -111,6 +127,22 @@ static inline bool __must_check > __must_check_overflow(bool overflow) > __val; \ > }) > > +/** > + * wrapping_assign_sub() - Intentionally perform a wrapping decrement assign > + * @var: variable to be decremented > + * @offset: amount to subtract > + * > + * Decrements @var by @offset with wrap-around. Returns the resulting > + * value of @var. Will not trip any wrap-around sanitizers. > + * > + * Returns the new value of @var. > + */ > +#define wrapping_assign_sub(var, offset) \ > + ({ \ > + typeof(var) *__ptr = &(var); \ > + *__ptr = wrapping_sub(typeof(var), *__ptr, offset); \ > + }) > + > /** > * check_mul_overflow() - Calculate multiplication with overflow checking > * @a: first factor > diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c > index d3fdb906d3fe..65e8a72a83bf 100644 > --- a/lib/overflow_kunit.c > +++ b/lib/overflow_kunit.c > @@ -284,6 +284,45 @@ DEFINE_TEST_ARRAY(s64) = { > "Unexpected wrap " #op " macro side-effect!\n"); \ > } while (0) > > +static int global_counter; > +static void bump_counter(void) > +{ > + global_counter++; > +} > + > +static int get_index(void) > +{ > + volatile int index = 0; > + bump_counter(); > + return index; > +} > + > +#define check_self_op(fmt, op, sym, a, b) do { > \ > + typeof(a + 0) _a = a; \ > + typeof(b + 0) _b = b; \ > + typeof(a + 0) _a_sym = a; \ > + typeof(a + 0) _a_orig[1] = { a }; \ > + typeof(b + 0) _b_orig = b; \ > + typeof(b + 0) _b_bump = b + 1; \ > + typeof(a + 0) _r; \ > + \ > + _a_sym sym _b; \ > + _r = wrapping_ ## op(_a, _b); \ > + KUNIT_EXPECT_TRUE_MSG(test, _r == _a_sym, \ > + "expected "fmt" "#op" "fmt" == "fmt", got "fmt"\n", \ > + a, b, _a_sym, _r); \ > + KUNIT_EXPECT_TRUE_MSG(test, _a == _a_sym, \ > + "expected "fmt" "#op" "fmt" == "fmt", got "fmt"\n", \ > + a, b, _a_sym, _a); \ > + /* Check for internal macro side-effects. */ \ > + global_counter = 0; \ > + wrapping_ ## op(_a_orig[get_index()], _b_orig++); \ > + KUNIT_EXPECT_EQ_MSG(test, global_counter, 1, \ > + "Unexpected wrapping_" #op " macro side-effect on arg1!\n"); \ > + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ > + "Unexpected wrapping_" #op " macro side-effect on arg2!\n"); \ > +} while (0) > + > #define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \ > static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \ > { \ > @@ -293,6 +332,10 @@ static void do_test_ ## n(struct kunit *test, const > struct test_ ## n *p) \ > check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of); \ > check_one_op(t, fmt, mul, "*", p->a, p->b, p->prod, p->p_of); \ > check_one_op(t, fmt, mul, "*", p->b, p->a, p->prod, p->p_of); \ > + /* wrapping_assign_{add,sub}() */ \ > + check_self_op(fmt, assign_add, +=, p->a, p->b); \ > + check_self_op(fmt, assign_add, +=, p->b, p->a); \ > + check_self_op(fmt, assign_sub, -=, p->a, p->b); \ > } \ > \ > static void n ## _overflow_test(struct kunit *test) { > \ > -- > 2.34.1 >
