From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D7EFC32771 for ; Mon, 26 Sep 2022 15:03:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235233AbiIZPDQ (ORCPT ); Mon, 26 Sep 2022 11:03:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60396 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235558AbiIZPCa (ORCPT ); Mon, 26 Sep 2022 11:02:30 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9A1B140A0 for ; Mon, 26 Sep 2022 06:34:45 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id A5447B8094E for ; Mon, 26 Sep 2022 13:34:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF2ECC433D6; Mon, 26 Sep 2022 13:34:41 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="Rv60Bf6L" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1664199280; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=313pwtBToP40WjGZK/I54DDFWUsiqmEDXM/dOhciNrY=; b=Rv60Bf6LZj2LCMhVj4ssLEc2q8EggalxCPmMtSRbKLnTKo5563NgG/KfUkcjuuUqAj1OJo li+cfZdBiGds5kuZcX4tO8poRPbNlHjiPmcUf2MsshvbQZ7QXKPlkZ+ExVkzewVxm1z/R6 niu6vuNlfBqmpU442Oxfp4Fe2auaptA= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id f7f8981b (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Mon, 26 Sep 2022 13:34:39 +0000 (UTC) From: "Jason A. Donenfeld" To: Andy Shevchenko , linux-kernel@vger.kernel.org, Andrew Morton , Kees Cook Cc: "Jason A. Donenfeld" Subject: [PATCH v3 1/2] minmax: sanity check constant bounds when clamping Date: Mon, 26 Sep 2022 15:34:34 +0200 Message-Id: <20220926133435.1333846-1-Jason@zx2c4.com> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The clamp family of functions only makes sense if hi>=lo. If hi and lo are compile-time constants, then raise a build error. Doing so has already caught buggy code. This also introduces the infrastructure to improve the clamping function in subsequent commits. Cc: Andy Shevchenko Cc: Andrew Morton Cc: Kees Cook Signed-off-by: Jason A. Donenfeld --- include/linux/minmax.h | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) diff --git a/include/linux/minmax.h b/include/linux/minmax.h index 5433c08fcc68..293a66ad7830 100644 --- a/include/linux/minmax.h +++ b/include/linux/minmax.h @@ -37,6 +37,28 @@ __cmp(x, y, op), \ __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op)) +#define __clamp(val, lo, hi) \ + __cmp(__cmp(val, lo, >), hi, <) + +#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \ + typeof(val) unique_val = (val); \ + typeof(lo) unique_lo = (lo); \ + typeof(hi) unique_hi = (hi); \ + __clamp(unique_val, unique_lo, unique_hi); }) + +#define __clamp_input_check(lo, hi) \ + (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ + __is_constexpr((lo) > (hi)), (lo) > (hi), false))) + +#define __careful_clamp(val, lo, hi) ({ \ + __clamp_input_check(lo, hi) + \ + __builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \ + __typecheck(hi, lo) && __is_constexpr(val) && \ + __is_constexpr(lo) && __is_constexpr(hi), \ + __clamp(val, lo, hi), \ + __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \ + __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); }) + /** * min - return minimum of two values of the same or compatible types * @x: first value @@ -86,7 +108,7 @@ * This macro does strict typechecking of @lo/@hi to make sure they are of the * same type as @val. See the unnecessary pointer comparisons. */ -#define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi) +#define clamp(val, lo, hi) __careful_clamp(val, lo, hi) /* * ..and if you can't take the strict @@ -121,7 +143,7 @@ * This macro does no typechecking and uses temporary variables of type * @type to make all the comparisons. */ -#define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi) +#define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi)) /** * clamp_val - return a value clamped to a given range using val's type -- 2.37.3