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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 049FAC433EF for ; Tue, 23 Nov 2021 05:42:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232969AbhKWFpy (ORCPT ); Tue, 23 Nov 2021 00:45:54 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:44084 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229471AbhKWFpw (ORCPT ); Tue, 23 Nov 2021 00:45:52 -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 169591FD5A; Tue, 23 Nov 2021 05:42:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637646164; 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=WFfl91pRcKjqye/TMhEYh56wAOGqJAk6Y4WkR2sBiHI=; b=LFz7uY9myDNF/P+QQ6Hs6HK3+8yVcp3PQGdPWUU1dKi5MQHALG6WpCJc3uu0sEduunUbQw N575J4oAZyBCoU9KSPBDb2akvDy8+tXb1v8Ee0tTeUSkIeVOG+ld4QYOWM/VGh9ToSVatS ubhEyiuxRpsOGtthFZ8/rIswmXp9uak= 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 DEF6413CE1; Tue, 23 Nov 2021 05:42:43 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id mlQ/NVN/nGF/PgAAMHmgww (envelope-from ); Tue, 23 Nov 2021 05:42:43 +0000 Subject: Re: [PATCH v3] xen: detect uninitialized xenbus in xenbus_init To: Stefano Stabellini Cc: boris.ostrovsky@oracle.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, jbeulich@suse.com, Stefano Stabellini , stable@vger.kernel.org References: <20211122221625.1473164-1-sstabellini@kernel.org> From: Juergen Gross Message-ID: <2533e721-a01b-6659-71fa-24a8d2896e84@suse.com> Date: Tue, 23 Nov 2021 06:42:43 +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: <20211122221625.1473164-1-sstabellini@kernel.org> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="bn1VCEjXOAIElom9Rm33lM2aD0v2rQP0n" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --bn1VCEjXOAIElom9Rm33lM2aD0v2rQP0n Content-Type: multipart/mixed; boundary="vgJhsb0FzDXqTZh0hVwNv70ek98hUO1L5"; protected-headers="v1" From: Juergen Gross To: Stefano Stabellini Cc: boris.ostrovsky@oracle.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, jbeulich@suse.com, Stefano Stabellini , stable@vger.kernel.org Message-ID: <2533e721-a01b-6659-71fa-24a8d2896e84@suse.com> Subject: Re: [PATCH v3] xen: detect uninitialized xenbus in xenbus_init References: <20211122221625.1473164-1-sstabellini@kernel.org> In-Reply-To: <20211122221625.1473164-1-sstabellini@kernel.org> --vgJhsb0FzDXqTZh0hVwNv70ek98hUO1L5 Content-Type: multipart/mixed; boundary="------------E19278278CC40697BA37CB60" Content-Language: en-US This is a multi-part message in MIME format. --------------E19278278CC40697BA37CB60 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 22.11.21 23:16, Stefano Stabellini wrote: > From: Stefano Stabellini >=20 > If the xenstore page hasn't been allocated properly, reading the value > of the related hvm_param (HVM_PARAM_STORE_PFN) won't actually return > error. Instead, it will succeed and return zero. Instead of attempting > to xen_remap a bad guest physical address, detect this condition and > return early. >=20 > Note that although a guest physical address of zero for > HVM_PARAM_STORE_PFN is theoretically possible, it is not a good choice > and zero has never been validly used in that capacity. >=20 > Also recognize the invalid value of INVALID_PFN which is ULLONG_MAX. >=20 > For 32-bit Linux, any pfn above ULONG_MAX would get truncated. Pfns > above ULONG_MAX should never be passed by the Xen tools to HVM guests > anyway, so check for this condition and return early. >=20 > Cc: stable@vger.kernel.org > Signed-off-by: Stefano Stabellini > --- > Changes in v3: > - improve in-code comment > - improve check >=20 > Changes in v2: > - add check for ULLONG_MAX (unitialized) > - add check for ULONG_MAX #if BITS_PER_LONG =3D=3D 32 (actual error) > - add pr_err error message > --- > drivers/xen/xenbus/xenbus_probe.c | 24 ++++++++++++++++++++++++ > 1 file changed, 24 insertions(+) >=20 > diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xen= bus_probe.c > index 94405bb3829e..d3ca57d48a73 100644 > --- a/drivers/xen/xenbus/xenbus_probe.c > +++ b/drivers/xen/xenbus/xenbus_probe.c > @@ -951,6 +951,30 @@ static int __init xenbus_init(void) > err =3D hvm_get_parameter(HVM_PARAM_STORE_PFN, &v); > if (err) > goto out_error; > + /* > + * 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. > + * > + * Also recognize the invalid value of INVALID_PFN which is > + * ULLONG_MAX. Adjust the comment, e.g. s/ULLONG_MAX/all bits set/ (in the commit message, too)? > + */ > + if (!v || !(v + 1)) { For me "if (!v || !~v)" would be more readable, but I don't really feel strong here. 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