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 lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 77ED6C531F8 for ; Thu, 23 Jul 2026 16:20:45 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wmw9u-00005g-D7; Thu, 23 Jul 2026 12:20:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wmw9q-0008WP-Mb for qemu-trivial@nongnu.org; Thu, 23 Jul 2026 12:20:26 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wmw9p-0001OC-1z for qemu-trivial@nongnu.org; Thu, 23 Jul 2026 12:20:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784823624; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=u4n7lwqGkv7gGrvOnha76mLZu76PJ3Gb+lZDI3u8mAU=; b=GRkp/O/hqz0I7TymcoHEr3jbNxEeT3TYyTqof4N9rrM+MmpB7HqB62HeYV4qvIU6BltyR+ NshZ/tEWJV1PR7hT/WJQg1f6/8w2qFZx8gm0QTSnfRtRWPo3b16/MBTiPEvoCWXUXmLZQ5 SWhKDT1Z5z+/XgUnxiTcurCiTJkWgKk= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-350-fr0jV-T2OYyTX3J6oJgiXQ-1; Thu, 23 Jul 2026 12:20:21 -0400 X-MC-Unique: fr0jV-T2OYyTX3J6oJgiXQ-1 X-Mimecast-MFC-AGG-ID: fr0jV-T2OYyTX3J6oJgiXQ_1784823619 Received: from mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.95]) (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 mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7292A1956067; Thu, 23 Jul 2026 16:20:19 +0000 (UTC) Received: from redhat.com (unknown [10.44.32.196]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2C7E9159F; Thu, 23 Jul 2026 16:20:16 +0000 (UTC) Date: Thu, 23 Jul 2026 17:20:13 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Cc: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , qemu-devel@nongnu.org, Dmitry Fleytman , qemu-trivial@nongnu.org, qemu-stable@nongnu.org Subject: Re: [PATCH v2] hw/display/vmware_vga: Don't allow guest to trigger long running loop in host Message-ID: References: <20260723124432.353969-1-thuth@redhat.com> <28b3741f-3cab-4e7c-b830-01fad0d80d35@oss.qualcomm.com> <7f8e11c2-f7ea-4362-9840-a295a7def315@redhat.com> MIME-Version: 1.0 In-Reply-To: <7f8e11c2-f7ea-4362-9840-a295a7def315@redhat.com> User-Agent: Mutt/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 X-Mimecast-MFC-PROC-ID: 70i4U7jhoFiF476IVALC4Z-WeRdudBwh0Sd5sL_iS5I_1784823619 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 3 X-Spam_score: 0.3 X-Spam_bar: / X-Spam_report: (0.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.951, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-trivial@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-trivial-bounces+qemu-trivial=archiver.kernel.org@nongnu.org Sender: qemu-trivial-bounces+qemu-trivial=archiver.kernel.org@nongnu.org On Thu, Jul 23, 2026 at 06:18:28PM +0200, Thomas Huth wrote: > On 23/07/2026 17.16, Daniel P. Berrangé wrote: > > On Thu, Jul 23, 2026 at 03:54:41PM +0200, Philippe Mathieu-Daudé wrote: > > > On 23/7/26 14:44, Thomas Huth wrote: > > > > From: Thomas Huth > > > > > > > > The code in the SVGA_CMD_DEFINE_ALPHA_CURSOR handler in vmsvga_fifo_run() > > > > basically does: > > > > > > > > x = vmsvga_fifo_read(s); > > > > y = vmsvga_fifo_read(s); > > > > args = x * y; > > > > goto badcmd; > > > > ... > > > > badcmd: > > > > len -= args; > > > > if (len < 0) { > > > > goto rewind; > > > > } > > > > while (args--) { > > > > vmsvga_fifo_read(s); > > > > } > > > > > > > > Thus by supplying huge values for x and y that overflow the result of > > > > the multiplication, the guest can trigger a long-running loop here > > > > that burns the host's CPU cycles. > > > > > > > > Add some sanity checks so that this cannot happen anymore. > > > > > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3782 > > > > Reported-by: Feifan Qian > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4026 > > > > Reported-by: Tristan Madani > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4076 > > > > Reported-by: Sunday Jiang > > > > Signed-off-by: Thomas Huth > > > > --- > > > > v2: Use SVGA_MAX_WIDTH and SVGA_MAX_HEIGHT instead of an arbitrary value > > > > > > > > hw/display/vmware_vga.c | 6 +++++- > > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/hw/display/vmware_vga.c b/hw/display/vmware_vga.c > > > > index f6f9edfd1d9..567806f0e47 100644 > > > > --- a/hw/display/vmware_vga.c > > > > +++ b/hw/display/vmware_vga.c > > > > @@ -737,6 +737,10 @@ static void vmsvga_fifo_run(struct vmsvga_state_s *s) > > > > vmsvga_fifo_read(s); > > > > x = vmsvga_fifo_read(s); > > > > y = vmsvga_fifo_read(s); > > > > + if (x < 0 || x >= SVGA_MAX_WIDTH || > > > > + y < 0 || y >= SVGA_MAX_HEIGHT) { > > > > > > vmsvga_fifo_read() returns unsigned... otherwise: > > > > But x & y are declared 'int', so at least on 32-bit builds > > a large uint32_t value would wrap and become negative. > > Although we dropped support for 32-bit platforms, IMHO it would > > be better to use uint32_t for 'x' and 'y' too rather than > > assuming the 'int' value won't be negative. > x and y are used as signed int all over the place here ... so reworking that > goes way beyond fixing this problem. Could we please get this patch merged > first for 11.1, and if someone then still feels like reworking the code, > this could be done for 11.2 ? Ok, then the < 0 checks should be kept. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|