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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 73358C433E0 for ; Wed, 3 Jun 2020 13:57:46 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 4E361207D5 for ; Wed, 3 Jun 2020 13:57:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4E361207D5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=eik.bme.hu Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37700 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jgTtp-0007CA-Ga for qemu-devel@archiver.kernel.org; Wed, 03 Jun 2020 09:57:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56822) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jgTt9-0006Gp-Pe for qemu-devel@nongnu.org; Wed, 03 Jun 2020 09:57:03 -0400 Received: from zero.eik.bme.hu ([152.66.115.2]:56510) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jgTt7-0004PU-4n for qemu-devel@nongnu.org; Wed, 03 Jun 2020 09:57:02 -0400 Received: from zero.eik.bme.hu (blah.eik.bme.hu [152.66.115.182]) by localhost (Postfix) with SMTP id A5F84746335; Wed, 3 Jun 2020 15:56:48 +0200 (CEST) Received: by zero.eik.bme.hu (Postfix, from userid 432) id 8BC8074632B; Wed, 3 Jun 2020 15:56:48 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by zero.eik.bme.hu (Postfix) with ESMTP id 8A32C74594E; Wed, 3 Jun 2020 15:56:48 +0200 (CEST) Date: Wed, 3 Jun 2020 15:56:48 +0200 (CEST) From: BALATON Zoltan To: Gerd Hoffmann Subject: Re: [PATCH] ati-vga: increment mm_index in ati_mm_read/write In-Reply-To: <20200603134404.xdb2koul7fatv4ez@sirius.home.kraxel.org> Message-ID: References: <20200603124732.1137892-1-ppandit@redhat.com> <20200603134404.xdb2koul7fatv4ez@sirius.home.kraxel.org> User-Agent: Alpine 2.22 (BSF 395 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Received-SPF: pass client-ip=152.66.115.2; envelope-from=balaton@eik.bme.hu; helo=zero.eik.bme.hu X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/03 09:56:49 X-ACL-Warn: Detected OS = FreeBSD 9.x or newer [fuzzy] X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Prasad J Pandit , Yi Ren , QEMU Developers , P J P , Ren Ding , Hanqing Zhao Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 3 Jun 2020, Gerd Hoffmann wrote: > On Wed, Jun 03, 2020 at 06:17:32PM +0530, P J P wrote: >> From: Prasad J Pandit >> >> While accessing VGA registers via ati_mm_read/write routines, >> a guest may set 's->regs.mm_index' such that it leads to infinite >> recursion. > > Lovely. > >> Increment the mm_index value to avoid it. > > Hmm, why modify mm_index? Shouldn't we just check it is non-zero > before calling ati_mm_read/ati_mm_write? I haven't found any mention in any docs that say MM_INDEX should auto increment so unless this is proven to do that on real hardware I also think forbiding indexed access to index registers should be enough. Regards, BALATON Zoltan