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Mon, 24 Feb 2020 16:05:02 +0000 (UTC) Received: from w520.home (ovpn-116-28.phx2.redhat.com [10.3.116.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id 65B7F5C1D6; Mon, 24 Feb 2020 16:04:59 +0000 (UTC) Date: Mon, 24 Feb 2020 09:04:58 -0700 From: Alex Williamson To: "Longpeng(Mike)" Subject: Re: [PATCH RESEND 1/3] vfio/pci: fix a null pointer reference in vfio_rom_read Message-ID: <20200224090458.080152c0@w520.home> In-Reply-To: <20200224064219.1434-2-longpeng2@huawei.com> References: <20200224064219.1434-1-longpeng2@huawei.com> <20200224064219.1434-2-longpeng2@huawei.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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: weifuqiang@huawei.com, arei.gonglei@huawei.com, huangzhichao@huawei.com, qemu-devel@nongnu.org, mst@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 24 Feb 2020 14:42:17 +0800 "Longpeng(Mike)" wrote: > From: Longpeng > > vfio_pci_load_rom() maybe failed and then the vdev->rom is NULL in > some situation (though I've not encountered yet), maybe we should > avoid the VM abort. > > Signed-off-by: Longpeng > --- > hw/vfio/pci.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c > index 5e75a95..ed798ae 100644 > --- a/hw/vfio/pci.c > +++ b/hw/vfio/pci.c > @@ -768,7 +768,7 @@ static void vfio_update_msi(VFIOPCIDevice *vdev) > } > } > > -static void vfio_pci_load_rom(VFIOPCIDevice *vdev) > +static bool vfio_pci_load_rom(VFIOPCIDevice *vdev) > { > struct vfio_region_info *reg_info; > uint64_t size; > @@ -778,7 +778,7 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev) > if (vfio_get_region_info(&vdev->vbasedev, > VFIO_PCI_ROM_REGION_INDEX, ®_info)) { > error_report("vfio: Error getting ROM info: %m"); > - return; > + return false; > } > > trace_vfio_pci_load_rom(vdev->vbasedev.name, (unsigned long)reg_info->size, > @@ -797,7 +797,7 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev) > error_printf("Device option ROM contents are probably invalid " > "(check dmesg).\nSkip option ROM probe with rombar=0, " > "or load from file with romfile=\n"); > - return; > + return false; > } > > vdev->rom = g_malloc(size); > @@ -849,6 +849,8 @@ static void vfio_pci_load_rom(VFIOPCIDevice *vdev) > data[6] = -csum; > } > } > + > + return true; > } > > static uint64_t vfio_rom_read(void *opaque, hwaddr addr, unsigned size) > @@ -863,8 +865,9 @@ static uint64_t vfio_rom_read(void *opaque, hwaddr addr, unsigned size) > uint64_t data = 0; > > /* Load the ROM lazily when the guest tries to read it */ > - if (unlikely(!vdev->rom && !vdev->rom_read_failed)) { > - vfio_pci_load_rom(vdev); > + if (unlikely(!vdev->rom && !vdev->rom_read_failed) && > + !vfio_pci_load_rom(vdev)) { > + return 0; > } > > memcpy(&val, vdev->rom + addr, Looks like an obvious bug, until you look at the rest of this memcpy(): memcpy(&val, vdev->rom + addr, (addr < vdev->rom_size) ? MIN(size, vdev->rom_size - addr) : 0); IOW, we'll do a zero sized memcpy() if rom_size is zero, so there's no risk of the concern identified in the commit log. This patch is unnecessary. Thanks, Alex