From patchwork Wed Aug 18 06:05:07 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 499483 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3057AC4338F for ; Wed, 18 Aug 2021 06:11:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1017560EBD for ; Wed, 18 Aug 2021 06:11:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238640AbhHRGMC (ORCPT ); Wed, 18 Aug 2021 02:12:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239090AbhHRGKP (ORCPT ); Wed, 18 Aug 2021 02:10:15 -0400 Received: from mail-pg1-x52b.google.com (mail-pg1-x52b.google.com [IPv6:2607:f8b0:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 48265C0698C9 for ; Tue, 17 Aug 2021 23:06:03 -0700 (PDT) Received: by mail-pg1-x52b.google.com with SMTP id 17so1141251pgp.4 for ; Tue, 17 Aug 2021 23:06:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=yj6MSRHjUgDQQeVVOJJG7wsN0XYzp0WPRrxqPpzxE8c=; b=CzXk1xRppwdRJolegZtv49GA2NFQ14/wBYjHzPVUV6FFSCAV81rN+Zkew6HAM1134z 9VMz6EAZM3OEiyOfJEz/43Jc+GeEg/kZ/l9C0CVoA8ABd/sj4sEJwPwqNtbgpylRBB0X jSjlWs/gCENWo/7C7d9KpfTsqLvHYTfxkxT94= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=yj6MSRHjUgDQQeVVOJJG7wsN0XYzp0WPRrxqPpzxE8c=; b=ixjxvXSpZ0/nC/czncNTzOrJQrrb361Zk7Zd97EMOQMhAnjB/vsFJzw/aW+H4pJ+Zo b6nIcY/fAGTt9W69CEqYySzExYnPKdJBrwcAwEAWu9RnAxKzOAIvS2iAOmznPCpjatTg kvnXNQkgxrFbAMt89B9U2B/VaFVJ/ksANxYBhsXfmTPRXamicR3jxVfV2sJ0AeiYT/4w PP0HZjnVPTY4qQiS8q0a14wFXCCyMQRL+/Z33RMkQE+HfuWTVCbonsu9tJ73vSIOqq1o XZ/ajNsCMy2BnLfHEbm7udrahyjrOmvULkZuLVnidHM+10DRSNmxAdDM3M+l1XygWmrT +d9Q== X-Gm-Message-State: AOAM5325azQc4SP8EFNaLLQhv0Vrniq4J3bQ4Cj9NUid2GG+w1pOL5k7 N/VlnOpZBb0c7ORI0o981jIgjA== X-Google-Smtp-Source: ABdhPJxiDT7B9pY6vGyClkQcsM0XG6Kg+GcLSvpUD3c8DNni73mb9LN7FVhCwNs3jsvIZgdTk/kz/A== X-Received: by 2002:aa7:850c:0:b0:3e2:edf3:3d09 with SMTP id v12-20020aa7850c000000b003e2edf33d09mr806951pfn.42.1629266763221; Tue, 17 Aug 2021 23:06:03 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id mr18sm3750578pjb.39.2021.08.17.23.05.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 17 Aug 2021 23:06:02 -0700 (PDT) From: Kees Cook To: linux-kernel@vger.kernel.org Cc: Kees Cook , Steffen Klassert , Herbert Xu , "David S. Miller" , Jakub Kicinski , Andrew Morton , Francis Laniel , Vincenzo Frascino , Daniel Axtens , netdev@vger.kernel.org, "Gustavo A. R. Silva" , Greg Kroah-Hartman , linux-wireless@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev, linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com, Rasmus Villemoes , linux-hardening@vger.kernel.org Subject: [PATCH v2 37/63] string.h: Introduce memset_after() for wiping trailing members/padding Date: Tue, 17 Aug 2021 23:05:07 -0700 Message-Id: <20210818060533.3569517-38-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210818060533.3569517-1-keescook@chromium.org> References: <20210818060533.3569517-1-keescook@chromium.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4092; h=from:subject; bh=ynt+tRmRAcx7nox2wqu1NNTkTOzsqx2+YTbDvMLTbxE=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBhHKMmwbMjodaindknTsBVe7537WHFelKIadd+u5e3 SxHIQdeJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYRyjJgAKCRCJcvTf3G3AJnBLEA CdNu7o5W+92HzRi1fko57n/mLwv/f7ERDN9lR9c1k1ZpJRD294w1BBHne+86h1ErieaOKABkA1tR9Z RPuVXQx84Ll35fJ448mje10Vlj4xMIsIO7I2+pCjPpZeZUknIkUAfgL4BIt11O1QZKIXt5gv0ApWLk F0vG/OdP1EsH7UfN0sGFW3dUPcQnV365DGpsYsXEbfYPUtv7V0sIo4u2EqY+DWjZNXgimvh1QDuwFD ASW7FG+u7LV5vdhie6SOhQtFr9ccWj/RPLaI95ILtuhSn99zvuAmxmiV9Sq50joZ8BHWNBKRMezCGO 3/YVBD1ioQyCyuoiDxeL9UMcrdPSZQt6aLznsfSXoKOqLO+Ir7tMR4XrhkEg8MfM+mA6JudX+GjyI5 HhSyIFjb1vJpco5l2tSPxCz4ioyocE52DQfc0wA9/yfi2liO4gbBZCqBmTCsIZpwdwhQkDkVBK5ZvR HOtc2ADG105U1yBtwAKKBM1Kpn6jPowZCs5D1qDOHYz1gAWljX17P6SuxaG3G/dMeo5MT0LpM97ZfJ VauEeeQUKsZsz2LSYtk7JsMuq3dNZ28R5tJc/mwglhdLai09Fi/99TDZ2wV4u2YvpwKr9UaxVWIuT5 e3kxAxaDFTyXoo70DNH9x1G7c+SuCaUbgMUIaDh6BALQ3dZqhLv+3W2zODmg== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org A common idiom in kernel code is to wipe the contents of a structure after a given member. This is especially useful in places where there is trailing padding. These open-coded cases are usually difficult to read and very sensitive to struct layout changes. Introduce a new helper, memset_after() that takes the target struct instance, the byte to write, and the member name after which the zeroing should start. Additionally adds memset_startat() for wiping trailing members _starting_ at a specific member instead of after a member, which is more readable in certain circumstances, but doesn't include any preceding padding. Cc: Steffen Klassert Cc: Herbert Xu Cc: "David S. Miller" Cc: Jakub Kicinski Cc: Andrew Morton Cc: Francis Laniel Cc: Vincenzo Frascino Cc: Daniel Axtens Cc: netdev@vger.kernel.org Signed-off-by: Kees Cook --- include/linux/string.h | 29 +++++++++++++++++++++++++++++ lib/test_memcpy.c | 24 ++++++++++++++++++++++++ 2 files changed, 53 insertions(+) diff --git a/include/linux/string.h b/include/linux/string.h index cbe889e404e2..fe56a1774207 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -272,6 +272,35 @@ static __always_inline void memcpy_and_pad(void *dest, size_t dest_len, memcpy(dest, src, dest_len); } +/** + * memset_after - Set a value after a struct member to the end of a struct + * + * @obj: Address of target struct instance + * @v: Byte value to repeatedly write + * @member: after which struct member to start writing bytes + * + * This is good for clearing padding following the given member. + */ +#define memset_after(obj, v, member) do { \ + memset((u8 *)(obj) + offsetofend(typeof(*(obj)), member), v, \ + sizeof(*(obj)) - offsetofend(typeof(*(obj)), member)); \ +} while (0) + +/** + * memset_startat - Set a value starting at a member to the end of a struct + * + * @obj: Address of target struct instance + * @v: Byte value to repeatedly write + * @member: struct member to start writing at + * + * Note that if there is padding between the prior member and the target + * member, memset_after() should be used to clear the prior padding. + */ +#define memset_startat(obj, v, member) do { \ + memset((u8 *)(obj) + offsetof(typeof(*(obj)), member), v, \ + sizeof(*(obj)) - offsetof(typeof(*(obj)), member)); \ +} while (0) + /** * str_has_prefix - Test if a string has a given prefix * @str: The string to test diff --git a/lib/test_memcpy.c b/lib/test_memcpy.c index be192b8e82b7..50bc99552a17 100644 --- a/lib/test_memcpy.c +++ b/lib/test_memcpy.c @@ -215,6 +215,20 @@ static void memset_test(struct kunit *test) 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, }, }; + struct some_bytes after = { + .data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x72, + 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, + 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, + 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, 0x72, + }, + }; + struct some_bytes startat = { + .data = { 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, + 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, + 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, + 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, + }, + }; struct some_bytes dest = { }; int count, value; u8 *ptr; @@ -245,6 +259,16 @@ static void memset_test(struct kunit *test) ptr += 8; memset(ptr++, value++, count++); compare("argument side-effects", dest, three); + + /* Verify memset_after() */ + dest = control; + memset_after(&dest, 0x72, three); + compare("memset_after()", dest, after); + + /* Verify memset_startat() */ + dest = control; + memset_startat(&dest, 0x79, four); + compare("memset_startat()", dest, startat); #undef TEST_OP }