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 lists.gnu.org (lists.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 DD696C636CC for ; Tue, 7 Feb 2023 21:46:18 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pPVmO-00051O-3Y; Tue, 07 Feb 2023 16:45:32 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pPVmM-00050O-8d for qemu-devel@nongnu.org; Tue, 07 Feb 2023 16:45:30 -0500 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 1pPVmK-0007zr-DZ for qemu-devel@nongnu.org; Tue, 07 Feb 2023 16:45:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675806327; h=from:from:reply-to:subject:subject: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=JoC59LVHpCa/1Ytt7TjtoZjqjVC+odBgqEpe+3vNfYY=; b=XVlKb0SyPyQQClvMq/KLCw6LZXeftsuSAe5ZKtBwXHtkqj9Ecge5bbL/VfGah9EzjxBSUa BwR6iISosyKkORMlswf3nJxIGpwPs6JqxWQwPVb/5c7/ZAA00HShPR0fZqEalxf92zagI8 78HXboj1JHmkWFbIQ+nYDgXSaWbVdGE= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-199-E72LuukDN_-3O05eysizfA-1; Tue, 07 Feb 2023 16:45:25 -0500 X-MC-Unique: E72LuukDN_-3O05eysizfA-1 Received: by mail-wm1-f72.google.com with SMTP id bg32-20020a05600c3ca000b003dc0df8c77dso55369wmb.6 for ; Tue, 07 Feb 2023 13:45:25 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=JoC59LVHpCa/1Ytt7TjtoZjqjVC+odBgqEpe+3vNfYY=; b=6zqm+2Bd714yuqslvdgHGq3U0zSJFH86bBVkYmD8OFXLnXEFDpnMLyDZdBsqHQCxkz 5X+yAGimWy9kUzMe9W0jKWla55JNfmHJLu4glRMgTBNT8oGXcG427Lco2uNyDuuX5jYX p/oNsIHtrv37HV5R6ub38QuKbyE7heaULoIrNq6JflvXgDqdgq/p4mP8h4ciiohhBjzj rDsRZ2APkEtPJdBYxJMLd524LTngYR+jgXbgvN+ENkJ2nj6b0fE6gCP4pnIpi64bXAfB 2rtMnuchtk2UrZu6vKDvNATVOzG6OW7UqXgsA4814P3Q1J3D3vbpuJ/cM2LNaJp5ZygG +Now== X-Gm-Message-State: AO0yUKVJTeUXJxQ+RCFh1cU0KULVmipRx28lFEo9antE6CaXi17KPCS0 h8xsIEpBCSEK9/ljA6tzyiTDnoMOMLIVOwTLG8Wnd+9t+Gh+O2c7Xt1z9v+iV7FNAFFpuAotn26 sc/bluiIsPutMZyU= X-Received: by 2002:adf:e40c:0:b0:2c3:ec55:b1b5 with SMTP id g12-20020adfe40c000000b002c3ec55b1b5mr4512139wrm.15.1675806324467; Tue, 07 Feb 2023 13:45:24 -0800 (PST) X-Google-Smtp-Source: AK7set/D0If38q8Hxv7rbjCqA+3CT2PcgMNNw80mtrJy6I3i2f9vwyOiBZ0DfI4K4Gt2gZyngz3mxw== X-Received: by 2002:adf:e40c:0:b0:2c3:ec55:b1b5 with SMTP id g12-20020adfe40c000000b002c3ec55b1b5mr4512121wrm.15.1675806324229; Tue, 07 Feb 2023 13:45:24 -0800 (PST) Received: from redhat.com ([2.52.8.17]) by smtp.gmail.com with ESMTPSA id h7-20020adffa87000000b002c3e698d7a4sm6717828wrr.24.2023.02.07.13.45.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Feb 2023 13:45:23 -0800 (PST) Date: Tue, 7 Feb 2023 16:45:19 -0500 From: "Michael S. Tsirkin" To: Dov Murik Cc: qemu-devel@nongnu.org, Tom Lendacky , "Jason A. Donenfeld" , James Bottomley , Gerd Hoffmann , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , "H. Peter Anvin" , Paolo Bonzini , Richard Henderson , Eduardo Habkost , Marcel Apfelbaum , Tobin Feldman-Fitzthum Subject: Re: [PATCH] x86: Don't add RNG seed to Linux cmdline for SEV guests Message-ID: <20230207164117-mutt-send-email-mst@kernel.org> References: <20230207084116.285787-1-dovmurik@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230207084116.285787-1-dovmurik@linux.ibm.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Feb 07, 2023 at 08:41:16AM +0000, Dov Murik wrote: > Recent feature to supply RNG seed to the guest kernel modifies the > kernel command-line by adding extra data at its end; this breaks > measured boot with SEV and OVMF, and possibly signed boot. > > Specifically SEV doesn't miss this feature because it uses UEFI/OVMF > which has its own way of getting random seed (not to mention that > getting the random seed from the untrusted host breaks the confidential > computing trust model). Nope - getting a random seed from an untrusted source should not break anything assuming you also have some other randomness source. If you don't then you have other problems. > Disable the RNG seed feature in SEV guests. > > Fixes: eac7a7791bb6 ("x86: don't let decompressed kernel image clobber setup_data") > Reported-by: Tom Lendacky > Signed-off-by: Dov Murik > > --- > > There might be a need for a wider change to the ways setup_data entries > are handled in x86_load_linux(); here I just try to restore the > situation for SEV guests prior to the addition of the SETUP_RNG_SEED > entry. > > Recent discussions on other (safer?) ways to pass this setup_data entry: > [1] https://lore.kernel.org/qemu-devel/da39abab9785aea2a2e7652ed6403b6268aeb31f.camel@linux.ibm.com/ > > Note that in qemu 7.2.0 this is broken as well -- there the > SETUP_RNG_SEED entry is appended to the Linux kernel data (and therefore > modifies and breaks the measurement of the kernel in SEV measured boot). > A similar fix will be needed there (but I fear this patch cannot be > applied as-is). So it's not a regression, is it? > --- > hw/i386/x86.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/hw/i386/x86.c b/hw/i386/x86.c > index eaff4227bd..e65a83f8df 100644 > --- a/hw/i386/x86.c > +++ b/hw/i386/x86.c > @@ -1103,7 +1103,7 @@ void x86_load_linux(X86MachineState *x86ms, > load_image_size(dtb_filename, setup_data->data, dtb_size); > } > > - if (!legacy_no_rng_seed && protocol >= 0x209) { > + if (!legacy_no_rng_seed && protocol >= 0x209 && !sev_enabled()) { > setup_data_offset = cmdline_size; > cmdline_size += sizeof(SetupData) + RNG_SEED_LENGTH; > kernel_cmdline = g_realloc(kernel_cmdline, cmdline_size); > > base-commit: 6661b8c7fe3f8b5687d2d90f7b4f3f23d70e3e8b I am beginning to think we have been hasty here. no rng seed should have been then default and requested with a flag. Then we'd avoid all this heartburn - and SEV might not be the only workload broken. Maybe not too late. Jason - objections? > -- > 2.25.1