Commit d219d2a9 authored by Kees Cook's avatar Kees Cook
Browse files

overflow: Allow mixed type arguments 

When the check_[op]_overflow() helpers were introduced, all arguments
were required to be the same type to make the fallback macros simpler.
However, now that the fallback macros have been removed[1], it is fine
to allow mixed types, which makes using the helpers much more useful,
as they can be used to test for type-based overflows (e.g. adding two
large ints but storing into a u8), as would be handy in the drm core[2].

Remove the restriction, and add additional self-tests that exercise
some of the mixed-type overflow cases, and double-check for accidental
macro side-effects.

[1] https://git.kernel.org/linus/4eb6bd55cfb22ffc20652732340c4962f3ac9a91
[2] https://lore.kernel.org/lkml/20220824084514.2261614-2-gwan-gyeong.mun@intel.com



Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: linux-hardening@vger.kernel.org
Reviewed-by: default avatarAndrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: default avatarGwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Tested-by: default avatarGwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 92d23c6e

include/linux/overflow.h

+41 −31
Original line number Diff line number Diff line
@@ -51,40 +51,50 @@ static inline bool __must_check __must_check_overflow(bool overflow) 
	return unlikely(overflow);

}



/*

 * For simplicity and code hygiene, the fallback code below insists on

 * a, b and *d having the same type (similar to the min() and max()

 * macros), whereas gcc's type-generic overflow checkers accept

 * different types. Hence we don't just make check_add_overflow an

 * alias for __builtin_add_overflow, but add type checks similar to

 * below.

/** check_add_overflow() - Calculate addition with overflow checking

 *

 * @a: first addend

 * @b: second addend

 * @d: pointer to store sum

 *

 * Returns 0 on success.

 *

 * *@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.

 */

#define check_add_overflow(a, b, d) __must_check_overflow(({	\

	typeof(a) __a = (a);			\

	typeof(b) __b = (b);			\

	typeof(d) __d = (d);			\

	(void) (&__a == &__b);			\

	(void) (&__a == __d);			\

	__builtin_add_overflow(__a, __b, __d);	\

}))

#define check_add_overflow(a, b, d)	\

	__must_check_overflow(__builtin_add_overflow(a, b, d))



#define check_sub_overflow(a, b, d) __must_check_overflow(({	\

	typeof(a) __a = (a);			\

	typeof(b) __b = (b);			\

	typeof(d) __d = (d);			\

	(void) (&__a == &__b);			\

	(void) (&__a == __d);			\

	__builtin_sub_overflow(__a, __b, __d);	\

}))

/** check_sub_overflow() - Calculate subtraction with overflow checking

 *

 * @a: minuend; value to subtract from

 * @b: subtrahend; value to subtract from @a

 * @d: pointer to store difference

 *

 * Returns 0 on success.

 *

 * *@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.

 */

#define check_sub_overflow(a, b, d)	\

	__must_check_overflow(__builtin_sub_overflow(a, b, d))



#define check_mul_overflow(a, b, d) __must_check_overflow(({	\

	typeof(a) __a = (a);			\

	typeof(b) __b = (b);			\

	typeof(d) __d = (d);			\

	(void) (&__a == &__b);			\

	(void) (&__a == __d);			\

	__builtin_mul_overflow(__a, __b, __d);	\

}))

/** check_mul_overflow() - Calculate multiplication with overflow checking

 *

 * @a: first factor

 * @b: second factor

 * @d: pointer to store product

 *

 * Returns 0 on success.

 *

 * *@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.

 */

#define check_mul_overflow(a, b, d)	\

	__must_check_overflow(__builtin_mul_overflow(a, b, d))



/** check_shl_overflow() - Calculate a left-shifted value and check overflow

 *

lib/overflow_kunit.c

+72 −29
Original line number Diff line number Diff line
@@ -16,12 +16,15 @@ 
#include <linux/types.h>

#include <linux/vmalloc.h>



#define DEFINE_TEST_ARRAY(t)			\

	static const struct test_ ## t {	\

		t a, b;				\

#define DEFINE_TEST_ARRAY_TYPED(t1, t2, t)			\

	static const struct test_ ## t1 ## _ ## t2 ## __ ## t {	\

		t1 a;						\

		t2 b;						\

		t sum, diff, prod;				\

		bool s_of, d_of, p_of;				\

	} t ## _tests[]

	} t1 ## _ ## t2 ## __ ## t ## _tests[]



#define DEFINE_TEST_ARRAY(t)	DEFINE_TEST_ARRAY_TYPED(t, t, t)



DEFINE_TEST_ARRAY(u8) = {

	{0, 0, 0, 0, 0, false, false, false},
@@ -223,8 +226,10 @@ DEFINE_TEST_ARRAY(s64) = { 
#endif



#define check_one_op(t, fmt, op, sym, a, b, r, of) do {			\

	t _r;							\

	int _a_orig = a, _a_bump = a + 1;				\

	int _b_orig = b, _b_bump = b + 1;				\

	bool _of;							\

	t _r;								\

									\

	_of = check_ ## op ## _overflow(a, b, &_r);			\

	KUNIT_EXPECT_EQ_MSG(test, _of, of,				\
@@ -233,10 +238,14 @@ DEFINE_TEST_ARRAY(s64) = { 
	KUNIT_EXPECT_EQ_MSG(test, _r, r,				\

		"expected "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"); \

} while (0)



#define DEFINE_TEST_FUNC(t, fmt)					\

static void do_test_ ## t(struct kunit *test, const struct test_ ## t *p) \

#define DEFINE_TEST_FUNC_TYPED(n, t, fmt)				\

static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \

{							   		\

	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);	\
@@ -245,15 +254,18 @@ static void do_test_ ## t(struct kunit *test, const struct test_ ## t *p) \ 
	check_one_op(t, fmt, mul, "*", p->b, p->a, p->prod, p->p_of);	\

}									\

									\

static void t ## _overflow_test(struct kunit *test) {			\

static void n ## _overflow_test(struct kunit *test) {			\

	unsigned i;							\

									\

	for (i = 0; i < ARRAY_SIZE(t ## _tests); ++i)			\

		do_test_ ## t(test, &t ## _tests[i]);			\

	for (i = 0; i < ARRAY_SIZE(n ## _tests); ++i)			\

		do_test_ ## n(test, &n ## _tests[i]);			\

	kunit_info(test, "%zu %s arithmetic tests finished\n",		\

		ARRAY_SIZE(t ## _tests), #t);				\

		ARRAY_SIZE(n ## _tests), #n);				\

}



#define DEFINE_TEST_FUNC(t, fmt)					\

	DEFINE_TEST_FUNC_TYPED(t ## _ ## t ## __ ## t, t, fmt)



DEFINE_TEST_FUNC(u8, "%d");

DEFINE_TEST_FUNC(s8, "%d");

DEFINE_TEST_FUNC(u16, "%d");
@@ -265,6 +277,33 @@ DEFINE_TEST_FUNC(u64, "%llu"); 
DEFINE_TEST_FUNC(s64, "%lld");

#endif



DEFINE_TEST_ARRAY_TYPED(u32, u32, u8) = {

	{0, 0, 0, 0, 0, false, false, false},

	{U8_MAX, 2, 1, U8_MAX - 2, U8_MAX - 1, true, false, true},

	{U8_MAX + 1, 0, 0, 0, 0, true, true, false},

};

DEFINE_TEST_FUNC_TYPED(u32_u32__u8, u8, "%d");



DEFINE_TEST_ARRAY_TYPED(u32, u32, int) = {

	{0, 0, 0, 0, 0, false, false, false},

	{U32_MAX, 0, -1, -1, 0, true, true, false},

};

DEFINE_TEST_FUNC_TYPED(u32_u32__int, int, "%d");



DEFINE_TEST_ARRAY_TYPED(u8, u8, int) = {

	{0, 0, 0, 0, 0, false, false, false},

	{U8_MAX, U8_MAX, 2 * U8_MAX, 0, U8_MAX * U8_MAX, false, false, false},

	{1, 2, 3, -1, 2, false, false, false},

};

DEFINE_TEST_FUNC_TYPED(u8_u8__int, int, "%d");



DEFINE_TEST_ARRAY_TYPED(int, int, u8) = {

	{0, 0, 0, 0, 0, false, false, false},

	{1, 2, 3, U8_MAX, 2, false, true, false},

	{-1, 0, U8_MAX, U8_MAX, 0, true, true, false},

};

DEFINE_TEST_FUNC_TYPED(int_int__u8, u8, "%d");



static void overflow_shift_test(struct kunit *test)

{

	int count = 0;
@@ -649,17 +688,21 @@ static void overflow_size_helpers_test(struct kunit *test) 
}



static struct kunit_case overflow_test_cases[] = {

	KUNIT_CASE(u8_overflow_test),

	KUNIT_CASE(s8_overflow_test),

	KUNIT_CASE(u16_overflow_test),

	KUNIT_CASE(s16_overflow_test),

	KUNIT_CASE(u32_overflow_test),

	KUNIT_CASE(s32_overflow_test),

	KUNIT_CASE(u8_u8__u8_overflow_test),

	KUNIT_CASE(s8_s8__s8_overflow_test),

	KUNIT_CASE(u16_u16__u16_overflow_test),

	KUNIT_CASE(s16_s16__s16_overflow_test),

	KUNIT_CASE(u32_u32__u32_overflow_test),

	KUNIT_CASE(s32_s32__s32_overflow_test),

/* Clang 13 and earlier generate unwanted libcalls on 32-bit. */

#if BITS_PER_LONG == 64

	KUNIT_CASE(u64_overflow_test),

	KUNIT_CASE(s64_overflow_test),

	KUNIT_CASE(u64_u64__u64_overflow_test),

	KUNIT_CASE(s64_s64__s64_overflow_test),

#endif

	KUNIT_CASE(u32_u32__u8_overflow_test),

	KUNIT_CASE(u32_u32__int_overflow_test),

	KUNIT_CASE(u8_u8__int_overflow_test),

	KUNIT_CASE(int_int__u8_overflow_test),

	KUNIT_CASE(overflow_shift_test),

	KUNIT_CASE(overflow_allocation_test),

	KUNIT_CASE(overflow_size_helpers_test),