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[109.67.62.195]) by smtp.gmail.com with ESMTPSA id s22sm3235617wmc.16.2020.03.26.06.29.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2020 06:29:44 -0700 (PDT) Date: Thu, 26 Mar 2020 09:29:41 -0400 From: "Michael S. Tsirkin" To: Igor Mammedov Subject: Re: acpi_pcihp_eject_slot() bug if passed 'slots == 0' Message-ID: <20200326092845-mutt-send-email-mst@kernel.org> References: <20200326132901.7aecb9e5@redhat.com> <20200326135041.297de118@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200326135041.297de118@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 01:50:41PM +0100, Igor Mammedov wrote: > On Thu, 26 Mar 2020 13:29:01 +0100 > Igor Mammedov wrote: >=20 > > 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 > >=20 > > 0 is not valid value, we should ignore and return early in this case > > like we do with bsel. I'll post a path shortly. > well, looking more that is only true for main bus, for bridges it can be > slot number can be zero, It can but we don't allow slot zero hotplug with SHPC so it's easier if we don't allow this with ACPI either. > then AML left shifts it and writes into B0EJ > which traps into pci_write(, data) and that is supposed to eject > slot 0 according to guest(AML). >=20 > Michael, > what's your take on it? >=20 > >=20 > > >=20 > > > thanks > > > -- PMM > > > =20 > >=20 > >=20