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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 6DC93C43381 for ; Fri, 22 Mar 2019 18:56:54 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 01D26218FE for ; Fri, 22 Mar 2019 18:56:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 01D26218FE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 44QtDd42BzzDqRk for ; Sat, 23 Mar 2019 05:56:49 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 44QtBp4VNDzDqLr for ; Sat, 23 Mar 2019 05:55:14 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) by bilbo.ozlabs.org (Postfix) with ESMTP id 44QtBp1jX8z8wMX for ; Sat, 23 Mar 2019 05:55:14 +1100 (AEDT) Received: by ozlabs.org (Postfix) id 44QtBp1Dcnz9sRd; Sat, 23 Mar 2019 05:55:14 +1100 (AEDT) Authentication-Results: ozlabs.org; spf=permerror (mailfrom) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 44QtBY0hVhz9sQp for ; Sat, 23 Mar 2019 05:54:59 +1100 (AEDT) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x2MIUAHk029368; Fri, 22 Mar 2019 13:30:24 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id x2MITmkv029327; Fri, 22 Mar 2019 13:29:48 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Fri, 22 Mar 2019 13:29:43 -0500 From: Segher Boessenkool To: Michael Ellerman Subject: Re: [PATCH v3] powerpc/64: Fix memcmp reading past the end of src/dest Message-ID: <20190322182943.GF3969@gate.crashing.org> References: <20190322123724.28435-1-mpe@ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190322123724.28435-1-mpe@ellerman.id.au> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@ozlabs.org, chandan@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Mar 22, 2019 at 11:37:24PM +1100, Michael Ellerman wrote: > .Lcmp_rest_lt8bytes: > - /* Here we have only less than 8 bytes to compare with. at least s1 > - * Address is aligned with 8 bytes. > - * The next double words are load and shift right with appropriate > - * bits. > + /* > + * Here we have less than 8 bytes to compare. At least s1 is aligned to > + * 8 bytes, but s2 may not be. We must make sure s2 + 8 doesn't cross a "s2 + 7"? The code is fine though (bgt, not bge). > + * page boundary, otherwise we might read past the end of the buffer and > + * trigger a page fault. We use 4K as the conservative minimum page > + * size. If we detect that case we go to the byte-by-byte loop. > + * > + * Otherwise the next double word is loaded from s1 and s2, and shifted > + * right to compare the appropriate bits. > */ > + clrldi r6,r4,(64-12) // r6 = r4 & 0xfff You can just write rlwinm r6,r4,0,0x0fff if that is clearer? Or do you still want a comment with that :-) > + cmpdi r6,0xff8 > + bgt .Lshort Reviewed-by: Segher Boessenkool Segher