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[109.64.41.91]) by smtp.gmail.com with ESMTPSA id x205sm22956704wmx.21.2020.06.08.00.08.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jun 2020 00:08:06 -0700 (PDT) Date: Mon, 8 Jun 2020 03:08:04 -0400 From: "Michael S. Tsirkin" To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Jason Wang , Pankaj Gupta , virtualization@lists.linux-foundation.org, teawater Subject: Re: [PATCH] virtio_mem: prevent overflow with subblock size Message-ID: <20200608030423-mutt-send-email-mst@kernel.org> References: <20200608061406.709211-1-mst@redhat.com> <0930c9d0-0708-c079-29bd-b80d4e3ce446@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0930c9d0-0708-c079-29bd-b80d4e3ce446@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 08, 2020 at 08:58:31AM +0200, David Hildenbrand wrote: > On 08.06.20 08:14, Michael S. Tsirkin wrote: > > If subblock size is large (e.g. 1G) 32 bit math involving it > > can overflow. Rather than try to catch all instances of that, > > let's tweak block size to 64 bit. > > I fail to see where we could actually trigger an overflow. The reported > warning looked like a false positive to me. So const uint64_t size = count * vm->subblock_size; is it unreasonable for count to be 4K with subblock_size being 1M? > > > > It ripples through UAPI which is an ABI change, but it's not too late to > > make it, and it will allow supporting >4Gbyte blocks while might > > become necessary down the road. > > > > This might break cloud-hypervisor, who's already implementing this > protocol upstream (ccing Hui). > https://github.com/cloud-hypervisor/cloud-hypervisor/blob/master/vm-virtio/src/mem.rs > > (blocks in the gigabyte range were never the original intention of > virtio-mem, but I am not completely opposed to that) So in that case, can you code up validation in the probe function? > > Fixes: 5f1f79bbc9e26 ("virtio-mem: Paravirtualized memory hotplug") > > Signed-off-by: Michael S. Tsirkin > > --- > > drivers/virtio/virtio_mem.c | 14 +++++++------- > > include/uapi/linux/virtio_mem.h | 4 ++-- > > 2 files changed, 9 insertions(+), 9 deletions(-) > > > > diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c > > index 2f357142ea5e..7b1bece8a331 100644 > > --- a/drivers/virtio/virtio_mem.c > > +++ b/drivers/virtio/virtio_mem.c > > @@ -77,7 +77,7 @@ struct virtio_mem { > > uint64_t requested_size; > > > > /* The device block size (for communicating with the device). */ > > - uint32_t device_block_size; > > + uint64_t device_block_size; > > /* The translated node id. NUMA_NO_NODE in case not specified. */ > > int nid; > > /* Physical start address of the memory region. */ > > @@ -86,7 +86,7 @@ struct virtio_mem { > > uint64_t region_size; > > > > /* The subblock size. */ > > - uint32_t subblock_size; > > + uint64_t subblock_size; > > /* The number of subblocks per memory block. */ > > uint32_t nb_sb_per_mb; > > > > @@ -1698,9 +1698,9 @@ static int virtio_mem_init(struct virtio_mem *vm) > > * - At least the device block size. > > * In the worst case, a single subblock per memory block. > > */ > > - vm->subblock_size = PAGE_SIZE * 1u << max_t(uint32_t, MAX_ORDER - 1, > > - pageblock_order); > > - vm->subblock_size = max_t(uint32_t, vm->device_block_size, > > + vm->subblock_size = PAGE_SIZE * 1ul << max_t(uint32_t, MAX_ORDER - 1, > > + pageblock_order); > > + vm->subblock_size = max_t(uint64_t, vm->device_block_size, > > vm->subblock_size); > > vm->nb_sb_per_mb = memory_block_size_bytes() / vm->subblock_size; > > > > @@ -1713,8 +1713,8 @@ static int virtio_mem_init(struct virtio_mem *vm) > > > > dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr); > > dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size); > > - dev_info(&vm->vdev->dev, "device block size: 0x%x", > > - vm->device_block_size); > > + dev_info(&vm->vdev->dev, "device block size: 0x%llx", > > + (unsigned long long)vm->device_block_size); > > dev_info(&vm->vdev->dev, "memory block size: 0x%lx", > > memory_block_size_bytes()); > > dev_info(&vm->vdev->dev, "subblock size: 0x%x", > > diff --git a/include/uapi/linux/virtio_mem.h b/include/uapi/linux/virtio_mem.h > > index a455c488a995..a9ffe041843c 100644 > > --- a/include/uapi/linux/virtio_mem.h > > +++ b/include/uapi/linux/virtio_mem.h > > @@ -185,10 +185,10 @@ struct virtio_mem_resp { > > > > struct virtio_mem_config { > > /* Block size and alignment. Cannot change. */ > > - __u32 block_size; > > + __u64 block_size; > > /* Valid with VIRTIO_MEM_F_ACPI_PXM. Cannot change. */ > > __u16 node_id; > > - __u16 padding; > > + __u8 padding[6]; > > /* Start address of the memory region. Cannot change. */ > > __u64 addr; > > /* Region size (maximum). Cannot change. */ > > > > > -- > Thanks, > > David / dhildenb