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Wed, 13 May 2020 08:16:50 +0000 (UTC) Date: Wed, 13 May 2020 10:16:37 +0200 From: Cornelia Huck To: Janosch Frank Subject: Re: [PATCH v1 2/8] s390/sclp: check sccb len before filling in data Message-ID: <20200513101637.2f325838.cohuck@redhat.com> In-Reply-To: <5ed5bc04-e4e3-21ca-057f-a978ef411ad8@linux.ibm.com> References: <20200508230823.22956-1-walling@linux.ibm.com> <20200508230823.22956-3-walling@linux.ibm.com> <58bc496c-28bb-26f8-ab46-aba6ad141717@linux.ibm.com> <737869a8-13b2-1831-00c6-629d5a109d9c@redhat.com> <05ab2e59-10c0-c7df-c014-b54883ddccd3@linux.ibm.com> <9a39a948-91a1-7cfe-f2a5-d30e5564f318@redhat.com> <20200512180140.4be69d60.cohuck@redhat.com> <5ed5bc04-e4e3-21ca-057f-a978ef411ad8@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; boundary="Sig_/QY_q6TYpcDHvMVu7kDcSeMB"; protocol="application/pgp-signature"; micalg=pgp-sha256 Received-SPF: pass client-ip=207.211.31.81; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/13 04:17:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Collin Walling , mst@redhat.com, David Hildenbrand , qemu-devel@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, svens@linux.ibm.com, pbonzini@redhat.com, mihajlov@linux.ibm.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --Sig_/QY_q6TYpcDHvMVu7kDcSeMB Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Wed, 13 May 2020 09:43:37 +0200 Janosch Frank wrote: > On 5/12/20 6:01 PM, Cornelia Huck wrote: > > On Mon, 11 May 2020 17:02:06 +0200 > > David Hildenbrand wrote: > > =20 > >> On 11.05.20 16:50, Janosch Frank wrote: =20 > >>> On 5/11/20 4:44 PM, David Hildenbrand wrote: =20 > >>>> On 11.05.20 16:36, Janosch Frank wrote: =20 > >>>>> On 5/9/20 1:08 AM, Collin Walling wrote: =20 > >>>>>> The SCCB must be checked for a sufficient length before it is fill= ed > >>>>>> with any data. If the length is insufficient, then the SCLP comman= d > >>>>>> is suppressed and the proper response code is set in the SCCB head= er. > >>>>>> > >>>>>> Signed-off-by: Collin Walling =20 > >>>>> > >>>>> Fixes tag? =20 > >=20 > > Probably > >=20 > > Fixes: 832be0d8a3bb ("s390x: sclp: Report insufficient SCCB length") > >=20 > > ? > > =20 > >>>>> Reviewed-by: Janosch Frank =20 > >>>> > >>>> This is not a fix AFAIKs. > >>>> sclp_service_call()/sclp_service_call_protected() always supplies a = full > >>>> SCCB of exactly 4k size. > >>>> =20 > >>> > >>> We don't check for QEMU's 4k buffer here, but for the length that was > >>> specified by the guest. > >>> > >>> It's valid for the guest to request cpu info and state that its buffe= r > >>> is only 1k. We can't write everything in 1k if we have ~200 cpus, so > >>> we'll report the insufficient length rc. > >>> > >>> What he fixes here is the time of the length check, it should be done > >>> before any changes are being done to the work_sccb. =20 > >> > >> I don't have access to the spec, especially, if the guest can expect > >> nothing else in the sccb to change in case we report an error code. So > >> whatever you tell me, I have to trust you :) =20 > >=20 > > Same here. Sounds plausible, but I have to trust the folks with the > > documentation :) > > =20 >=20 > The AR states that: > * Command validity check (has prio over length, as length is dependent > on command) > * boundary (if extended-length is not available) > * Sufficient length check >=20 > are done before "any other command action is taken". > If a test fails the command is suppressed. 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