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[109.67.62.195]) by smtp.gmail.com with ESMTPSA id l83sm3497881wmf.43.2020.03.26.06.28.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2020 06:28:26 -0700 (PDT) Date: Thu, 26 Mar 2020 09:28:23 -0400 From: "Michael S. Tsirkin" To: Igor Mammedov Subject: Re: acpi_pcihp_eject_slot() bug if passed 'slots == 0' Message-ID: <20200326092535-mutt-send-email-mst@kernel.org> References: <20200326142317.018c13e1@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200326142317.018c13e1@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 63.128.21.74 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: Peter Maydell , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Mar 26, 2020 at 02:23:17PM +0100, Igor Mammedov wrote: > On Thu, 26 Mar 2020 11:52:36 +0000 > Peter Maydell wrote: >=20 > > Hi; Coverity spots that if hw/acpi/pcihp.c:acpi_pcihp_eject_slot() > > is passed a zero 'slots' argument then ctz32(slots) will return 32, > > and then the code that does '1U << slot' is C undefined behaviour > > because it's an oversized shift. (This is CID 1421896.) > >=20 > > Since the pci_write() function in this file can call > > acpi_pcihp_eject_slot() with an arbitrary value from the guest, > > I think we need to handle 'slots =3D=3D 0' safely. But what should > > the behaviour be? >=20 > it also uncovers a bug, where we are not able to eject slot 0 on bridge, And that is by design. A standard PCI SHPC register can support up to 31 hotpluggable slots. So we chose slot 0 as non hotpluggable. It's consistent across SHPC, PCI-E, so I made ACPI match. You can't hot-add it either. > can be reproduced with: >=20 > -enable-kvm -m 4G -device pci-bridge,chassis_nr=3D1 -global PIIX4_PM.acp= i-pci-hotplug-with-bridge-support=3Don -device virtio-net-pci,bus=3Dpci.1,a= ddr=3D0,id=3Dnetdev12 >=20 > (monitor) device_del netdev12 > (monitor) qtree # still shows the device >=20 > reason is that acpi_pcihp_eject_slot() > if (PCI_SLOT(dev->devfn) =3D=3D slot) { # doesn't match (0 !=3D 32) >=20 > so device is not deleted We should probably teach QEMU that some slots aren't hotpluggable even if device in it is hotpluggable in theory. But that is a separate issue. > > thanks > > -- PMM > >=20