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 08506E77184 for ; Thu, 19 Dec 2024 18:02:37 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tOKqE-0006rH-QK; Thu, 19 Dec 2024 13:01:43 -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 1tOKq5-0006qi-IB for qemu-devel@nongnu.org; Thu, 19 Dec 2024 13:01:34 -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 1tOKq1-0005cZ-8v for qemu-devel@nongnu.org; Thu, 19 Dec 2024 13:01:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1734631286; 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=54pDTFQxW9OpbnsdR+FouKMaCByKwry4P/Ob9hi5NVg=; b=gEKaR7g4348rDL9e0AIrElGJ8nZIILCf6YMTqTI5fQ6gHVGJYW5JMIQuidnwXNEEJsJmlk E0mHzA8xhpI2k20OB3v4T4VXOpJ12QlzfGPgx/tDqa3K3dVhDp5klJNJDrt94tNlp+eACC eMpZzgsAlxymiSzOuo/ptisLb4Ckzn4= Received: from mx-prod-mc-02.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-411-q64UCY0rPkuXH02NgZt-VA-1; Thu, 19 Dec 2024 13:01:23 -0500 X-MC-Unique: q64UCY0rPkuXH02NgZt-VA-1 X-Mimecast-MFC-AGG-ID: q64UCY0rPkuXH02NgZt-VA Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D279E1956057; Thu, 19 Dec 2024 18:01:20 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.54]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9FED730044C1; Thu, 19 Dec 2024 18:01:17 +0000 (UTC) Date: Thu, 19 Dec 2024 18:01:14 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Michael Roth Cc: qemu-devel@nongnu.org, pbonzini@redhat.com, eduardo@habkost.net, armbru@redhat.com, pankaj.gupta@amd.com, huibo.wang@amd.com, jroedel@suse.com, dionnaglaze@google.com Subject: Re: [PATCH v1 3/3] i386/sev: Add KVM_EXIT_SNP_REQ_CERTS support for certificate-fetching Message-ID: References: <20241218154939.1114831-1-michael.roth@amd.com> <20241218154939.1114831-4-michael.roth@amd.com> <20241218222951.v6yjhcd7j6uojcs4@amd.com> <20241219131601.ckebfuxy5ukpdcml@amd.com> <20241219174949.wtmw7gosb4hkfjxg@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241219174949.wtmw7gosb4hkfjxg@amd.com> User-Agent: Mutt/2.2.13 (2024-03-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 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=-1.116, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Dec 19, 2024 at 11:49:49AM -0600, Michael Roth wrote: > On Thu, Dec 19, 2024 at 01:37:18PM +0000, Daniel P. Berrangé wrote: > > IMHO we msut consider unlink() to be a valid thing, because the right > > way for apps to perform crash safe atomic updates of existing files, > > is to use rename() from a temporary file, and the rename() in has an > > implicit unlink as part of its operation. ie apps would be doing: > > > > fd = open("foo.tmp") > > write(fd, ...) > > fsync(fd) > > close(fd) > > rename("foo.tmp", "foo") > > If we still want to allow for this rather than enforcing in-place > update, one alternative would be to just allow a separate lock file > to be specified rather than locking the certificate file itself. That > would provide a bit more flexibility. > > I can update the QEMU implementation to take -certs-lock-file in > addition to -certs-file so they can be specified separately. And if > -certs-lock-file is not specified then QEMU will just assume > management handles things different or has agreed to not do endorsement > key updates while SNP guests are running. > > I think we'd considered something like that originally but the thinking > was that locking the certs themselves was more organic in terms of an > "obvious"/natural solution. But it does end up being a bit more > inflexible WRT how libraries/etc. might manage file updates underneath > the covers, so maybe a lock file is the better approach after all. If we want locking, I think locking the certs file directly is a nicer idea, as it avoids everyone having to agree on the location of the lock file, relative to the certs file. The current locking code just needs to go inside a while(1) loop and have fstat + stat added to detect the recreation race. For example: https://gitlab.com/libvirt/libvirt/-/blob/master/src/util/virpidfile.c#L376 With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|