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Message-Id: <20240130220614.1154497-5-keescook@chromium.org>
Date: Tue, 30 Jan 2024 14:06:10 -0800
From: Kees Cook <keescook@...omium.org>
To: Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc: Kees Cook <keescook@...omium.org>,
Mark Rutland <mark.rutland@....com>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
Justin Stitt <justinstitt@...gle.com>,
linux-hardening@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Bill Wendling <morbo@...gle.com>,
Miguel Ojeda <ojeda@...nel.org>,
Marco Elver <elver@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Przemek Kitszel <przemyslaw.kitszel@...el.com>,
Masahiro Yamada <masahiroy@...nel.org>,
linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev
Subject: [PATCH v2 5/5] overflow: Introduce inc_wrap() and dec_wrap()
This allows replacements of the idioms "var += offset" and "var -= offset"
with the inc_wrap() and dec_wrap() 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@...vas.dk>
Cc: Mark Rutland <mark.rutland@....com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Justin Stitt <justinstitt@...gle.com>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
include/linux/overflow.h | 28 +++++++++++++++++++++
lib/overflow_kunit.c | 54 ++++++++++++++++++++++++++++++++++------
2 files changed, 75 insertions(+), 7 deletions(-)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index c9139f88578b..075c30218145 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -138,6 +138,20 @@ static inline bool __must_check __must_check_overflow(bool overflow)
__val; \
})
+/**
+ * inc_wrap() - Intentionally perform a wrapping increment
+ * @a: variable to be incremented
+ * @b: amount to add
+ *
+ * Increments @a by @b with wrap-around. Returns the resulting
+ * value of @a. Will not trip any wrap-around sanitizers.
+ */
+#define inc_wrap(var, offset) \
+ ({ \
+ typeof(var) *__ptr = &(var); \
+ *__ptr = add_wrap(typeof(var), *__ptr, offset); \
+ })
+
/**
* check_sub_overflow() - Calculate subtraction with overflow checking
* @a: minuend; value to subtract from
@@ -169,6 +183,20 @@ static inline bool __must_check __must_check_overflow(bool overflow)
__val; \
})
+/**
+ * dec_wrap() - Intentionally perform a wrapping decrement
+ * @a: variable to be decremented
+ * @b: amount to subtract
+ *
+ * Decrements @a by @b with wrap-around. Returns the resulting
+ * value of @a. Will not trip any wrap-around sanitizers.
+ */
+#define dec_wrap(var, offset) \
+ ({ \
+ typeof(var) *__ptr = &(var); \
+ *__ptr = sub_wrap(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 319f950872bd..46af7ccde0c6 100644
--- a/lib/overflow_kunit.c
+++ b/lib/overflow_kunit.c
@@ -265,36 +265,76 @@ 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_TRUE_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_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected " #op " macro side-effect!\n"); \
- KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op " macro side-effect!\n"); \
+ KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected check " #op " macro side-effect!\n"); \
+ KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected check " #op " macro side-effect!\n"); \
\
_r = op ## _wrap(t, a, b); \
KUNIT_EXPECT_TRUE_MSG(test, _r == r, \
- "expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \
+ "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 = op ## _wrap(t, _a_orig++, _b_orig++); \
- KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected " #op " macro side-effect!\n"); \
- KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op " macro side-effect!\n"); \
+ KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected wrap " #op " macro side-effect!\n"); \
+ KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "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 = op ## _wrap(_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; \
+ op ## _wrap(_a_orig[get_index()], _b_orig++); \
+ KUNIT_EXPECT_EQ_MSG(test, global_counter, 1, "Unexpected " #op "_wrap() macro side-effect on arg1!\n"); \
+ KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op "_wrap() 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) \
{ \
+ /* check_{add,sub,mul}_overflow() and {add,sub,mul}_wrap() */ \
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); \
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); \
+ /* {inc,dec}_wrap() */ \
+ 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
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