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Wed, 18 Nov 2020 00:53:24 -0800 (PST) X-Google-Smtp-Source: ABdhPJxgJD1o8ywEY4t4OQIueQbAmql3gTIcIP3ShzGrCx4YODX1q4Qn+IpCiMfdyPRRZSprJkgIxZPBIAhVZGzZUaA= X-Received: by 2002:a50:9b02:: with SMTP id o2mr1251194edi.208.1605689604221; Wed, 18 Nov 2020 00:53:24 -0800 (PST) MIME-Version: 1.0 References: <20201113103113.223239-1-mcascell@redhat.com> In-Reply-To: From: Mauro Matteo Cascella Date: Wed, 18 Nov 2020 09:53:13 +0100 Message-ID: Subject: Re: [PATCH v2] net/e1000e_core: adjust count if RDH exceeds RDT in e1000e_ring_advance() To: Jason Wang Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mcascell@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=63.128.21.124; envelope-from=mcascell@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/17 19:41:43 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_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: gaoning.pgn@antgroup.com, 330cjfdn@gmail.com, Dmitry Fleytman , Laszlo Ersek , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Nov 18, 2020 at 4:56 AM Jason Wang wrote: > > > On 2020/11/13 =E4=B8=8B=E5=8D=886:31, Mauro Matteo Cascella wrote: > > The e1000e_write_packet_to_guest() function iterates over a set of > > receive descriptors by advancing rx descriptor head register (RDH) from > > its initial value to rx descriptor tail register (RDT). The check in > > e1000e_ring_empty() is responsible for detecting whether RDH has reache= d > > RDT, terminating the loop if that's the case. Additional checks have > > been added in the past to deal with bogus values submitted by the guest > > to prevent possible infinite loop. This is done by "wrapping around" RD= H > > at some point and detecting whether it assumes the original value durin= g > > the loop. > > > > However, when e1000e is configured to use the packet split feature, RDH= is > > incremented by two instead of one, as the packet split descriptors are > > 32 bytes while regular descriptors are 16 bytes. A malicious or buggy > > guest may set RDT to an odd value and transmit only null RX descriptors= . > > This corner case would prevent RDH from ever matching RDT, leading to a= n > > infinite loop. This patch adds a check in e1000e_ring_advance() to make= sure > > RDH does not exceed RDT in a single incremental step, adjusting the cou= nt > > value accordingly. > > > Can this patch solve this issue in another way? > > https://patchew.org/QEMU/20201111130636.2208620-1-ppandit@redhat.com/ > > Thanks > Yes, it does work nicely. Still, I think this patch is useful to avoid possible inconsistent state in e1000e_ring_advance() when count > 1. Thank you, --=20 Mauro Matteo Cascella Red Hat Product Security PGP-Key ID: BB3410B0