v7: - further kern-doc cleanups (Mark)
v6: https://lore.kernel.org/all/[email protected]/
v5: https://lore.kernel.org/all/[email protected]/
v4: https://lore.kernel.org/all/[email protected]/
v3: https://lore.kernel.org/all/[email protected]/
v2: https://lore.kernel.org/all/[email protected]/
v1: https://lore.kernel.org/all/[email protected]/
Hi,
In preparation for gaining instrumentation for signed[1], unsigned[2], and
pointer[3] wrap-around, expand the overflow header to include wrap-around
helpers that can be used to annotate arithmetic where wrapped calculations
are expected (e.g. atomics).
After spending time getting the unsigned integer wrap-around sanitizer
running warning-free on a basic x86_64 boot[4], I think the add/sub/mul
helpers first argument being the output type makes the most sense (as
suggested by Rasmus).
-Kees
Link: https://github.com/KSPP/linux/issues/26 [1]
Link: https://github.com/KSPP/linux/issues/27 [2]
Link: https://github.com/KSPP/linux/issues/344 [3]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=devel/overflow/enable-unsigned-sanitizer [4]
Kees Cook (3):
overflow: Adjust check_*_overflow() kern-doc to reflect results
overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul()
overflow: Introduce wrapping_assign_add() and wrapping_assign_sub()
include/linux/overflow.h | 101 ++++++++++++++++++++++++++++++++++-----
lib/overflow_kunit.c | 67 ++++++++++++++++++++++++--
2 files changed, 152 insertions(+), 16 deletions(-)
--
2.34.1
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 <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
---
Cc: Mark Rutland <[email protected]>
Cc: [email protected]
---
include/linux/overflow.h | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 7b5cf4a5cd19..ad64d810c8aa 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -57,11 +57,10 @@ static inline bool __must_check __must_check_overflow(bool overflow)
* @b: second addend
* @d: pointer to store sum
*
- * Returns 0 on success.
+ * Returns true on wrap-around, false otherwise.
*
- * *@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, regardless of whether
+ * wrap-around occurred.
*/
#define check_add_overflow(a, b, d) \
__must_check_overflow(__builtin_add_overflow(a, b, d))
@@ -72,11 +71,10 @@ 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 true on wrap-around, false otherwise.
*
- * *@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, regardless of whether
+ * wrap-around occurred.
*/
#define check_sub_overflow(a, b, d) \
__must_check_overflow(__builtin_sub_overflow(a, b, d))
@@ -87,11 +85,10 @@ static inline bool __must_check __must_check_overflow(bool overflow)
* @b: second factor
* @d: pointer to store product
*
- * Returns 0 on success.
+ * Returns true on wrap-around, false otherwise.
*
- * *@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, regardless of whether
+ * wrap-around occurred.
*/
#define check_mul_overflow(a, b, d) \
__must_check_overflow(__builtin_mul_overflow(a, b, d))
--
2.34.1
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.
Reviewed-by: Gustavo A. R. Silva <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Acked-by: Mark Rutland <[email protected]>
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: [email protected]
---
include/linux/overflow.h | 48 ++++++++++++++++++++++++++++++++++++++++
lib/overflow_kunit.c | 24 ++++++++++++++++----
2 files changed, 68 insertions(+), 4 deletions(-)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index ad64d810c8aa..d3ff8e2bec29 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -65,6 +65,22 @@ 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; \
+ __builtin_add_overflow(a, b, &__val); \
+ __val; \
+ })
+
/**
* check_sub_overflow() - Calculate subtraction with overflow checking
* @a: minuend; value to subtract from
@@ -79,6 +95,22 @@ 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; \
+ __builtin_sub_overflow(a, b, &__val); \
+ __val; \
+ })
+
/**
* check_mul_overflow() - Calculate multiplication with overflow checking
* @a: first factor
@@ -93,6 +125,22 @@ 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; \
+ __builtin_mul_overflow(a, b, &__val); \
+ __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); \
--
2.34.1
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]
---
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
On Wed, 14 Feb 2024 at 20:46, Kees Cook <[email protected]> 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]>
Reviewed-by: Marco Elver <[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]
> ---
> 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
[...]
> + /* 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); \
> } \
Merely a curiosity, and am not suggesting this for this patch: I
wonder how much of this could be tested at compile-time. These are
very primitive operations, so I suspect the compiler could either
check these in a static_assert(), or if some of it isn't
constexpr-friendly, after optimizations with a BUILD_BUG.
On Wed, Feb 14, 2024 at 11:46:01AM -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 <[email protected]>
> Signed-off-by: Kees Cook <[email protected]>
> ---
> Cc: Mark Rutland <[email protected]>
> Cc: [email protected]
Acked-by: Mark Rutland <[email protected]>
Mark.
> ---
> include/linux/overflow.h | 21 +++++++++------------
> 1 file changed, 9 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 7b5cf4a5cd19..ad64d810c8aa 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -57,11 +57,10 @@ static inline bool __must_check __must_check_overflow(bool overflow)
> * @b: second addend
> * @d: pointer to store sum
> *
> - * Returns 0 on success.
> + * Returns true on wrap-around, false otherwise.
> *
> - * *@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, regardless of whether
> + * wrap-around occurred.
> */
> #define check_add_overflow(a, b, d) \
> __must_check_overflow(__builtin_add_overflow(a, b, d))
> @@ -72,11 +71,10 @@ 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 true on wrap-around, false otherwise.
> *
> - * *@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, regardless of whether
> + * wrap-around occurred.
> */
> #define check_sub_overflow(a, b, d) \
> __must_check_overflow(__builtin_sub_overflow(a, b, d))
> @@ -87,11 +85,10 @@ static inline bool __must_check __must_check_overflow(bool overflow)
> * @b: second factor
> * @d: pointer to store product
> *
> - * Returns 0 on success.
> + * Returns true on wrap-around, false otherwise.
> *
> - * *@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, regardless of whether
> + * wrap-around occurred.
> */
> #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 11:46:03AM -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
>