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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id q4sm5765337wrs.56.2021.11.04.11.18.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Nov 2021 11:18:12 -0700 (PDT) Date: Thu, 4 Nov 2021 18:18:10 +0000 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH 1/3] sev/i386: Allow launching with -kernel if no OVMF hashes table found Message-ID: References: <20211101102136.1706421-1-dovmurik@linux.ibm.com> <20211101102136.1706421-2-dovmurik@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.648, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: , Cc: Tom Lendacky , Ashish Kalra , Brijesh Singh , Eduardo Habkost , James Bottomley , Marcelo Tosatti , qemu-devel@nongnu.org, Dov Murik , Tobin Feldman-Fitzthum , Paolo Bonzini , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrangé (berrange@redhat.com) wrote: > On Mon, Nov 01, 2021 at 10:21:34AM +0000, Dov Murik wrote: > > Commit cff03145ed3c ("sev/i386: Introduce sev_add_kernel_loader_hashes > > for measured linux boot", 2021-09-30) introduced measured direct boot > > with -kernel, using an OVMF-designated hashes table which QEMU fills. > > > > However, if OVMF doesn't designate such an area, QEMU would completely > > abort the VM launch. This breaks launching with -kernel using older > > OVMF images which don't publish the SEV_HASH_TABLE_RV_GUID. > > > > Instead, just warn the user that -kernel was supplied by OVMF doesn't > > specify the GUID for the hashes table. The following warning will be > > displayed during VM launch: > > > > qemu-system-x86_64: warning: SEV: kernel specified but OVMF has no hash table guid > > > > Signed-off-by: Dov Murik > > Reported-by: Tom Lendacky > > --- > > target/i386/sev.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/target/i386/sev.c b/target/i386/sev.c > > index eede07f11d..682b8ccf6c 100644 > > --- a/target/i386/sev.c > > +++ b/target/i386/sev.c > > @@ -1204,7 +1204,7 @@ bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp) > > int aligned_len; > > > > if (!pc_system_ovmf_table_find(SEV_HASH_TABLE_RV_GUID, &data, NULL)) { > > - error_setg(errp, "SEV: kernel specified but OVMF has no hash table guid"); > > + warn_report("SEV: kernel specified but OVMF has no hash table guid"); > > return false; > > I'm pretty wary of doing this kind of thing. > > If someone is using QEMU and they required to have the hashes populated > for their use case, they now don't get a fatal error if something goes > wrong with the process. This is bad as it hides a serious mistake. > > If someone is using QEMU and they don't require to have the hashes > populated and they knowingly use a firmware that doesn't support > this, they'll now get a irrelevant warning every time they boot > QEMU. This is bad because IME users will file bugs complaining > about this bogus warning. > > > If we genuinely need to support both uses cases, then we should have > an explicit command line flag to request the desired behaviour. > > This could be a -machine option to indicate that the hashes must > be populated. > > - unset: try to populate hashes, *silently* ignore missing table > in ovmf > - set == on: try to populate hashes, report error on missing > table in ovmf > -set == off: never try to populate hashes, nor look for the > table in ovmf Or as a property on the sev-guest object. Dave > 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 :| > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK