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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D660BC433EF for ; Thu, 18 Nov 2021 08:54:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA39F6108B for ; Thu, 18 Nov 2021 08:54:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244821AbhKRI5L (ORCPT ); Thu, 18 Nov 2021 03:57:11 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:55468 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244914AbhKRI4N (ORCPT ); Thu, 18 Nov 2021 03:56:13 -0500 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id B01551FD35; Thu, 18 Nov 2021 08:53:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637225591; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=kb4waLBtBGSXHBRlUIyKFLdUUKY/+94sspf4DGh5uNQ=; b=QY+YOrdxtpHrGcCGhkhih+HiCvAEBJoMyKspFVIHYod3K9u1/U2wsVq0W6Q2rFa98WDnaz lTdmfLpr7cAOnfSDRrJMdtJCcyjn1tSTHLFyr+rwP/ACrllPWoc9DrlkOoU/1jQ/EoCgDD VmVPN/Lb9MT8UV38B+dNLpzZJflncvQ= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 7BBDC13CF6; Thu, 18 Nov 2021 08:53:11 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id ItXeHHcUlmEQYQAAMHmgww (envelope-from ); Thu, 18 Nov 2021 08:53:11 +0000 Subject: Re: [PATCH] xen: detect uninitialized xenbus in xenbus_init To: Jan Beulich Cc: boris.ostrovsky@oracle.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Stefano Stabellini , stable@vger.kernel.org, Stefano Stabellini References: <20211117021145.3105042-1-sstabellini@kernel.org> <2592121c-ed62-c346-5aeb-37adb6bb1982@suse.com> <44403efe-a850-b53b-785f-6f5c73eb2b96@suse.com> <9453672e-56ea-71cd-cdd2-b4aaafb8db56@suse.com> From: Juergen Gross Message-ID: Date: Thu, 18 Nov 2021 09:53:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <9453672e-56ea-71cd-cdd2-b4aaafb8db56@suse.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="xzOlgh1CbAovcTzGLiZmCHxZ9bARs5goq" Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --xzOlgh1CbAovcTzGLiZmCHxZ9bARs5goq Content-Type: multipart/mixed; boundary="5BnwnPOSA5BhoJPL6QLfBvrjsgylFqXtS"; protected-headers="v1" From: Juergen Gross To: Jan Beulich Cc: boris.ostrovsky@oracle.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Stefano Stabellini , stable@vger.kernel.org, Stefano Stabellini Message-ID: Subject: Re: [PATCH] xen: detect uninitialized xenbus in xenbus_init References: <20211117021145.3105042-1-sstabellini@kernel.org> <2592121c-ed62-c346-5aeb-37adb6bb1982@suse.com> <44403efe-a850-b53b-785f-6f5c73eb2b96@suse.com> <9453672e-56ea-71cd-cdd2-b4aaafb8db56@suse.com> In-Reply-To: <9453672e-56ea-71cd-cdd2-b4aaafb8db56@suse.com> --5BnwnPOSA5BhoJPL6QLfBvrjsgylFqXtS Content-Type: multipart/mixed; boundary="------------D1D8945FCC5D2D680FE05F6A" Content-Language: en-US This is a multi-part message in MIME format. --------------D1D8945FCC5D2D680FE05F6A Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 18.11.21 09:47, Jan Beulich wrote: > On 18.11.2021 06:32, Juergen Gross wrote: >> On 18.11.21 03:37, Stefano Stabellini wrote: >>> --- a/drivers/xen/xenbus/xenbus_probe.c >>> +++ b/drivers/xen/xenbus/xenbus_probe.c >>> @@ -951,6 +951,28 @@ static int __init xenbus_init(void) >>> err =3D hvm_get_parameter(HVM_PARAM_STORE_PFN, &v); >>> if (err) >>> goto out_error; >>> + /* >>> + * Return error on an invalid value. >>> + * >>> + * Uninitialized hvm_params are zero and return no error. >>> + * Although it is theoretically possible to have >>> + * HVM_PARAM_STORE_PFN set to zero on purpose, in reality it is >>> + * not zero when valid. If zero, it means that Xenstore hasn't >>> + * been properly initialized. Instead of attempting to map a >>> + * wrong guest physical address return error. >>> + */ >>> + if (v =3D=3D 0) { >> >> Make this "if (v =3D=3D ULONG_MAX || v=3D=3D 0)" instead? >> This would result in the same err on a new and an old hypervisor >> (assuming we switch the hypervisor to init params with ~0UL). >> >>> + err =3D -ENOENT; >>> + goto out_error; >>> + } >>> + /* >>> + * ULONG_MAX is invalid on 64-bit because is INVALID_PFN. >>> + * On 32-bit return error to avoid truncation. >>> + */ >>> + if (v >=3D ULONG_MAX) { >>> + err =3D -EINVAL; >>> + goto out_error; >>> + } >> >> Does it make sense to continue the system running in case of >> truncation? This would be a 32-bit guest with more than 16TB of RAM >> and the Xen tools decided to place the Xenstore ring page above the >> 16TB boundary. This is a completely insane scenario IMO. >> >> A proper panic() in this case would make diagnosis of that much >> easier (me having doubts that this will ever be hit, though). >=20 > While I agree panic() may be an option here (albeit I'm not sure why > that would be better than trying to cope with 0 and hence without I could imagine someone wanting to run a guest without Xenstore access, which BTW will happen in case of a guest created by the hypervisor at boot time. > xenbus), I'd like to point out that the amount of RAM assigned to a > guest is unrelated to the choice of GFNs for the various "magic" > items. Yes, but this would still be a major tools problem which probably would render the whole guest rather unusable. 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