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 09D07C433F5 for ; Tue, 23 Nov 2021 21:07:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239879AbhKWVLB (ORCPT ); Tue, 23 Nov 2021 16:11:01 -0500 Received: from mail.kernel.org ([198.145.29.99]:40564 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235483AbhKWVLA (ORCPT ); Tue, 23 Nov 2021 16:11:00 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6925D6023D; Tue, 23 Nov 2021 21:07:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1637701671; bh=fmNL3u7OnTxHOXgiEAfETI2VUP4gGL2FJ5fr15s9qbA=; h=From:To:Cc:Subject:Date:From; b=Rxsf9g172XeXrnTMElnISWoUxpvJaJP4/7s1u7MpinNCISK6oeUbHJW/lpgH8JGsB puD4+oFyzmduElLopaiyTeolLisu1Xf48UOOd4Un7crdq7xpFMv57i1F0JviSNa/cZ jcXfA0lzTIp+uyHcrihkikmb99s425RVXRl7DVQhONTi4A8d606fnVMK1Xr1srsjUQ 24+5RmfZXbOsHUaWs7Wi/yKoWYF0eePtcIGng1H8cU3Hgm+STQZLefqQwQUOisJ3Ro PVh6ejIW8QkefCdwF19gP37QgiNPsfHFGc7TIbjDvT5LESWy4QMWr6vgzF/whZ+9pK xlFCgZB5syF1Q== From: Stefano Stabellini To: jgross@suse.com Cc: boris.ostrovsky@oracle.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, sstabellini@kernel.org, jbeulich@suse.com, Stefano Stabellini , stable@vger.kernel.org Subject: [PATCH v4] xen: detect uninitialized xenbus in xenbus_init Date: Tue, 23 Nov 2021 13:07:48 -0800 Message-Id: <20211123210748.1910236-1-sstabellini@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Stefano Stabellini 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. 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. Also recognize all bits set as an invalid value. 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. Cc: stable@vger.kernel.org Signed-off-by: Stefano Stabellini --- Changes in v4: - say "all bits set" instead of INVALID_PFN - improve check Changes in v3: - improve in-code comment - improve check Changes in v2: - add check for ULLONG_MAX (unitialized) - add check for ULONG_MAX #if BITS_PER_LONG == 32 (actual error) - add pr_err error message drivers/xen/xenbus/xenbus_probe.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c index 94405bb3829e..251b26439733 100644 --- a/drivers/xen/xenbus/xenbus_probe.c +++ b/drivers/xen/xenbus/xenbus_probe.c @@ -951,6 +951,29 @@ static int __init xenbus_init(void) err = 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 all bits set as an invalid value. + */ + if (!v || !~v) { + err = -ENOENT; + goto out_error; + } + /* Avoid truncation on 32-bit. */ +#if BITS_PER_LONG == 32 + if (v > ULONG_MAX) { + pr_err("%s: cannot handle HVM_PARAM_STORE_PFN=%llx > ULONG_MAX\n", + __func__, v); + err = -EINVAL; + goto out_error; + } +#endif xen_store_gfn = (unsigned long)v; xen_store_interface = xen_remap(xen_store_gfn << XEN_PAGE_SHIFT, -- 2.25.1