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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 5B54BC169C4 for ; Fri, 8 Feb 2019 06:13:54 +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 63DF120811 for ; Fri, 8 Feb 2019 06:13:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 63DF120811 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au 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 43wlHg1y4zzDqWH for ; Fri, 8 Feb 2019 17:13:51 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (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 43wlG073L8zDqKJ for ; Fri, 8 Feb 2019 17:12:24 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix) id 43wlG05crcz9sLw; Fri, 8 Feb 2019 17:12:24 +1100 (AEDT) Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPSA id 43wlG04yh4z9s3x; Fri, 8 Feb 2019 17:12:24 +1100 (AEDT) From: Michael Ellerman To: Segher Boessenkool Subject: Re: [PATCH v2] powerpc/64: Fix memcmp reading past the end of src/dest In-Reply-To: <20190207125256.GW14180@gate.crashing.org> References: <20190207115313.31078-1-mpe@ellerman.id.au> <20190207125256.GW14180@gate.crashing.org> Date: Fri, 08 Feb 2019 17:12:21 +1100 Message-ID: <87bm3mkdve.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain 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, npiggin@gmail.com, daniel@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Segher Boessenkool writes: > On Thu, Feb 07, 2019 at 10:53:13PM +1100, Michael Ellerman wrote: >> Chandan reported that fstests' generic/026 test hit a crash: > >> The instruction dump decodes as: >> subfic r6,r5,8 >> rlwinm r6,r6,3,0,28 >> ldbrx r9,0,r3 >> ldbrx r10,0,r4 <- >> >> Which shows us doing an 8 byte load from c00000062ac3fff9, which >> crosses the page boundary at c00000062ac40000 and faults. >> >> It's not OK for memcmp to read past the end of the source or >> destination buffers. > > It's not okay to access memory pages unsolicited. Reading past the end > is fine per se. Yeah I guess that's true. Things like KASAN/valgrind probably disagree, but KASAN at least overrides memcmp AIUI. I guess I feel better about it not reading past the end of the buffers, but maybe I'm being paranoid. The other complication is we support multiple page sizes, so detecting a page boundary is more complicated than it could be. So I guess I'm inclined to stick with this approach, but I can update the change log. cheers