* [PATCH v4 0/3] overflow: Introduce wrapping helpers
@ 2024-02-06 10:31 Kees Cook
2024-02-06 10:31 ` [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Kees Cook
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Kees Cook @ 2024-02-06 10:31 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Kees Cook, Gustavo A. R. Silva, Marco Elver, Eric Biggers,
Mark Rutland, Andrew Morton, linux-kernel, linux-hardening
v4:
- use __builtin directly (marco)
- rename to wrapping_* (eric)
- update kern-doc (rasmus)
v3: https://lore.kernel.org/all/20240205090854.make.507-kees@kernel.org/
v2: https://lore.kernel.org/all/20240130220218.it.154-kees@kernel.org/
v1: https://lore.kernel.org/lkml/20240129182845.work.694-kees@kernel.org/
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_inc() and wrapping_dec()
include/linux/overflow.h | 104 ++++++++++++++++++++++++++++++++++-----
lib/overflow_kunit.c | 67 +++++++++++++++++++++++--
2 files changed, 155 insertions(+), 16 deletions(-)
--
2.34.1
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results
2024-02-06 10:31 [PATCH v4 0/3] overflow: Introduce wrapping helpers Kees Cook
@ 2024-02-06 10:31 ` Kees Cook
2024-02-06 16:36 ` Gustavo A. R. Silva
2024-02-06 10:31 ` [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul() Kees Cook
2024-02-06 10:31 ` [PATCH v4 3/3] overflow: Introduce wrapping_inc() and wrapping_dec() Kees Cook
2 siblings, 1 reply; 7+ messages in thread
From: Kees Cook @ 2024-02-06 10:31 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Kees Cook, Gustavo A. R. Silva, linux-hardening, Marco Elver,
Eric Biggers, Mark Rutland, Andrew Morton, linux-kernel
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.
Cc: "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.
*
- * *@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))
--
2.34.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul()
2024-02-06 10:31 [PATCH v4 0/3] overflow: Introduce wrapping helpers Kees Cook
2024-02-06 10:31 ` [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Kees Cook
@ 2024-02-06 10:31 ` Kees Cook
2024-02-06 16:54 ` Gustavo A. R. Silva
2024-02-06 10:31 ` [PATCH v4 3/3] overflow: Introduce wrapping_inc() and wrapping_dec() Kees Cook
2 siblings, 1 reply; 7+ messages in thread
From: Kees Cook @ 2024-02-06 10:31 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Kees Cook, Marco Elver, Eric Biggers, Mark Rutland,
linux-hardening, Gustavo A . R . Silva, Andrew Morton,
linux-kernel
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; \
+ })
+
/**
* 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); \
--
2.34.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v4 3/3] overflow: Introduce wrapping_inc() and wrapping_dec()
2024-02-06 10:31 [PATCH v4 0/3] overflow: Introduce wrapping helpers Kees Cook
2024-02-06 10:31 ` [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Kees Cook
2024-02-06 10:31 ` [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul() Kees Cook
@ 2024-02-06 10:31 ` Kees Cook
2 siblings, 0 replies; 7+ messages in thread
From: Kees Cook @ 2024-02-06 10:31 UTC (permalink / raw)
To: Rasmus Villemoes
Cc: Kees Cook, Marco Elver, Eric Biggers, Mark Rutland,
Gustavo A. R. Silva, linux-hardening, Andrew Morton,
linux-kernel
This allows replacements of the idioms "var += offset" and "var -= offset"
with the wrapping_inc() and wrapping_dec() helpers respectively. They
will avoid wrap-around sanitizer instrumentation.
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: "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 | 32 ++++++++++++++++++++++++++++++
lib/overflow_kunit.c | 43 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 75 insertions(+)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 429c4d61a940..8ab68350f976 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -82,6 +82,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
__val; \
})
+/**
+ * wrapping_inc() - Intentionally perform a wrapping increment
+ * @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_inc(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
@@ -113,6 +129,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
__val; \
})
+/**
+ * wrapping_dec() - Intentionally perform a wrapping decrement
+ * @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_dec(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..6cadce8f8a47 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_{inc,dec}() */ \
+ check_self_op(fmt, inc, +=, p->a, p->b); \
+ check_self_op(fmt, inc, +=, p->b, p->a); \
+ check_self_op(fmt, dec, -=, p->a, p->b); \
} \
\
static void n ## _overflow_test(struct kunit *test) { \
--
2.34.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results
2024-02-06 10:31 ` [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Kees Cook
@ 2024-02-06 16:36 ` Gustavo A. R. Silva
0 siblings, 0 replies; 7+ messages in thread
From: Gustavo A. R. Silva @ 2024-02-06 16:36 UTC (permalink / raw)
To: Kees Cook, Rasmus Villemoes
Cc: Gustavo A. R. Silva, linux-hardening, Marco Elver, Eric Biggers,
Mark Rutland, Andrew Morton, linux-kernel
On 2/6/24 04:31, 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.
>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
Better to be concise and direct. 🙂
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Thanks!
--
Gustavo
> ---
> 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.
> *
> - * *@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))
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul()
2024-02-06 10:31 ` [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul() Kees Cook
@ 2024-02-06 16:54 ` Gustavo A. R. Silva
2024-02-07 9:35 ` Kees Cook
0 siblings, 1 reply; 7+ messages in thread
From: Gustavo A. R. Silva @ 2024-02-06 16:54 UTC (permalink / raw)
To: Kees Cook, Rasmus Villemoes
Cc: Marco Elver, Eric Biggers, Mark Rutland, linux-hardening,
Gustavo A . R . Silva, Andrew Morton, linux-kernel
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
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul()
2024-02-06 16:54 ` Gustavo A. R. Silva
@ 2024-02-07 9:35 ` Kees Cook
0 siblings, 0 replies; 7+ messages in thread
From: Kees Cook @ 2024-02-07 9:35 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Rasmus Villemoes, Marco Elver, Eric Biggers, Mark Rutland,
linux-hardening, Gustavo A . R . Silva, Andrew Morton,
linux-kernel
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.
--
Kees Cook
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2024-02-07 9:35 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-02-06 10:31 [PATCH v4 0/3] overflow: Introduce wrapping helpers Kees Cook
2024-02-06 10:31 ` [PATCH v4 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Kees Cook
2024-02-06 16:36 ` Gustavo A. R. Silva
2024-02-06 10:31 ` [PATCH v4 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul() Kees Cook
2024-02-06 16:54 ` Gustavo A. R. Silva
2024-02-07 9:35 ` Kees Cook
2024-02-06 10:31 ` [PATCH v4 3/3] overflow: Introduce wrapping_inc() and wrapping_dec() Kees Cook
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.