From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CE3BE446A1; Mon, 19 Feb 2024 17:03:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708362204; cv=none; b=Hcu0m2nyow0DOCqikn6Xld+0IYMAzaWuUJWobbdYwSSg9ATyHrUu4IHnhXprsTme0aW3z7V1W4gidvZRuPJIERGrCvmsYZJidbRiz4XGkNT4qVRPGn4TaDbtT63cCtw9EhOtXUMNqvt9pmhn/YzhJOISC5L0KVKiFBUTziFbPAA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708362204; c=relaxed/simple; bh=MJvYvJVcGAJ+lPRgCUqoBB/EzpB7glN7S5T8DbEhTSM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SHALQbjDsld0kps5IzuuaPIz/58d3rsRqX0gPh0gb5ok/sz4jY/TV5cpsxTRru39IIPKxG8jCsoXW6QxAx00n0zckZnmyCaHY1dO3ZsCaUpBoq6iai5GvYDIsafGFDF0Zdt5G2bm7HdzDA8O4iJwxkMg7YEE/56qGERW32wncz0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 11670DA7; Mon, 19 Feb 2024 09:04:02 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.67.88]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D4D963F7CE; Mon, 19 Feb 2024 09:03:20 -0800 (PST) Date: Mon, 19 Feb 2024 17:03:18 +0000 From: Mark Rutland To: Kees Cook Cc: Andy Shevchenko , Rasmus Villemoes , Marco Elver , Eric Biggers , "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org, Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 3/3] overflow: Introduce wrapping_assign_add() and wrapping_assign_sub() Message-ID: References: <20240214194432.makes.837-kees@kernel.org> <20240214194605.602505-3-keescook@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240214194605.602505-3-keescook@chromium.org> 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 > --- > Cc: Rasmus Villemoes > Cc: Marco Elver > Cc: Eric Biggers > Cc: Mark Rutland > Cc: "Gustavo A. R. Silva" > Cc: linux-hardening@vger.kernel.org Acked-by: Mark Rutland 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 >