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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 17388C433F5 for ; Tue, 5 Oct 2021 22:13:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6AFC76113E for ; Tue, 5 Oct 2021 22:13:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6AFC76113E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id EDD08900002; Tue, 5 Oct 2021 18:13:12 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E8C9B6B0071; Tue, 5 Oct 2021 18:13:12 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D7B89900002; Tue, 5 Oct 2021 18:13:12 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0197.hostedemail.com [216.40.44.197]) by kanga.kvack.org (Postfix) with ESMTP id C97DE6B006C for ; Tue, 5 Oct 2021 18:13:12 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 8EC0918033E58 for ; Tue, 5 Oct 2021 22:13:12 +0000 (UTC) X-FDA: 78663785424.25.5FA1A83 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf29.hostedemail.com (Postfix) with ESMTP id D2BC8900803C for ; Tue, 5 Oct 2021 22:13:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=xsVlpZTTNkhlhMPNdgScKU+eVt1a1DIoBtHHpEw2KSE=; b=rV024NIMkBOIe+ckIi2eT9BqS3 agoSxH9B/UelQTNMCfQUJOirLOAAdpXkjyWBOhCIK9kea7rJ67cknSz5M7MpJgri26PxiUg9O/cID PSQbSQQ6wW5AKX+sRzLaj3zKLEsAExIm6FQ2AU0W7G9InBUTgZUivBv5JF9Urj3NQJts+iMlNMSY6 igiu37XB+Fh+DOe2uM1hhS/z8GsdYcwx3VG282JMhZfbJIhQ/qSRaGQq7Ji8lrD3/zf6OfCmR5V72 Z82eypzVmi/ZdbtyZ0lje9CphHiilV4VhHcAArW+wXq0UiNUNQ0LHRTrfHA2LJ5Af68w+Pah/1Snm me/YOKEg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mXsg3-000Jt7-I9; Tue, 05 Oct 2021 22:12:54 +0000 Date: Tue, 5 Oct 2021 23:12:47 +0100 From: Matthew Wilcox To: Kees Cook Cc: linux-mm@kvack.org, Thomas Gleixner Subject: Re: [PATCH 3/3] mm/usercopy: Detect compound page overruns Message-ID: References: <20211004224224.4137992-1-willy@infradead.org> <20211004224224.4137992-4-willy@infradead.org> <202110051425.ABFA413@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202110051425.ABFA413@keescook> X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D2BC8900803C X-Stat-Signature: k3b117bsndbrxoq3qbcef5y7n93swuny Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=rV024NIM; dmarc=none; spf=none (imf29.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-HE-Tag: 1633471991-689030 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Oct 05, 2021 at 02:26:37PM -0700, Kees Cook wrote: > On Mon, Oct 04, 2021 at 11:42:23PM +0100, Matthew Wilcox (Oracle) wrote: > > + } else if (PageHead(page)) { > > + /* A compound allocation */ > > + if (ptr + n > page_address(page) + page_size(page)) > > + usercopy_abort("page alloc", NULL, to_user, 0, n); > > "0" could be "ptr - page_address(page)", I think? With that: > > Acked-by: Kees Cook Right, so that can be: } else if (PageHead(page)) { /* A compound allocation */ unsigned long offset = ptr - page_address(page); if (offset + n > page_size(page)) usercopy_abort("page alloc", NULL, to_user, offset, n); which saves us calling page_address() twice. Probably GCC is smart enough to CSE it anyway, but it also avoids splitting at the 80 column boundary ;-)