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 989A7C531D1 for ; Thu, 23 Jul 2026 15:17:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wmvAj-0002lv-T4; Thu, 23 Jul 2026 11:17:17 -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 1wmvAA-0002eB-UO for qemu-trivial@nongnu.org; Thu, 23 Jul 2026 11:16:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wmvA7-0007ge-3M for qemu-trivial@nongnu.org; Thu, 23 Jul 2026 11:16:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1784819795; 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=enhLSCDm+JTvTkDF94wbrSZR+KPQTNZKlc2ClwZQM5E=; b=S7dR8rQxeKQh+IfgTuWMHtU77TNSex0R1bP10nRw97bQnWiC7/NnDq+j12OUgIyWvdVbzS 0vv3ydXAZ5dbMV/WMtymS4Adk6YAc3afsOIWwmq1CPXT6zjTyGY1iovRCdXwpjqJ+L0x5L gcwOolIlidiUJUy9HDKYDW93/rbzqu8= Received: from mx-prod-mc-03.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-33-I4kGMtJkMM-ftGmudo5brA-1; Thu, 23 Jul 2026 11:16:33 -0400 X-MC-Unique: I4kGMtJkMM-ftGmudo5brA-1 X-Mimecast-MFC-AGG-ID: I4kGMtJkMM-ftGmudo5brA_1784819792 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2FB4D1954B25; Thu, 23 Jul 2026 15:16:32 +0000 (UTC) Received: from redhat.com (unknown [10.44.32.196]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CFF54196B09F; Thu, 23 Jul 2026 15:16:29 +0000 (UTC) Date: Thu, 23 Jul 2026 16:16:26 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Cc: Thomas Huth , 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> MIME-Version: 1.0 In-Reply-To: <28b3741f-3cab-4e7c-b830-01fad0d80d35@oss.qualcomm.com> User-Agent: Mutt/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-MFC-PROC-ID: HjGLQEMmMOSp1rWmuaOIHiZOcPDKYQz-qvhTDOreyh0_1784819792 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: permerror client-ip=170.10.129.124; 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_H2=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=0.01 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 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. > Reviewed-by: Philippe Mathieu-Daudé > > > + goto rewind; > > + } > > args = x * y; > > goto badcmd; > > case SVGA_CMD_RECT_ROP_FILL: > > @@ -776,7 +780,7 @@ static void vmsvga_fifo_run(struct vmsvga_state_s *s) > > if (len < 0) { > > goto rewind; > > } > > - while (args--) { > > + while (args-- > 0) { > > vmsvga_fifo_read(s); > > } > > printf("%s: Unknown command 0x%02x in SVGA command FIFO\n", > > 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 :|