From b28e0506fafd9c987bba7a6a71ea02a37fcabdea Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Thu, 25 Dec 2014 16:03:27 +0200 Subject: [PATCH 1/2] virtio_ring: document alignment requirements Host needs to know vring element alignment requirements: simply doing alignof on structures doesn't work reliably: on some platforms gcc has alignof(uint32_t) == 2. Add macros for alignment as specified in virtio 1.0 cs01, export them to userspace as well. Acked-by: Rusty Russell Signed-off-by: Michael S. Tsirkin --- include/uapi/linux/virtio_ring.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h index 61c818a7fe70d..a3318f31e8e7f 100644 --- a/include/uapi/linux/virtio_ring.h +++ b/include/uapi/linux/virtio_ring.h @@ -101,6 +101,13 @@ struct vring { struct vring_used *used; }; +/* Alignment requirements for vring elements. + * When using pre-virtio 1.0 layout, these fall out naturally. + */ +#define VRING_AVAIL_ALIGN_SIZE 2 +#define VRING_USED_ALIGN_SIZE 4 +#define VRING_DESC_ALIGN_SIZE 16 + /* The standard layout for the ring is a continuous chunk of memory which looks * like this. We assume num is a power of 2. * From 5d9a07b0de512b77bf28d2401e5fe3351f00a240 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Sun, 21 Dec 2014 01:00:23 +0200 Subject: [PATCH 2/2] vhost: relax used address alignment virtio 1.0 only requires used address to be 4 byte aligned, vhost required 8 bytes (size of vring_used_elem). Fix up vhost to match that. Additionally, while vhost correctly requires 8 byte alignment for log, it's unconnected to used ring: it's a consequence that log has u64 entries. Tweak code to make that clearer. Signed-off-by: Michael S. Tsirkin --- drivers/vhost/vhost.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index ed71b5347a766..cb807d0ea498d 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -713,9 +713,13 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp) r = -EFAULT; break; } - if ((a.avail_user_addr & (sizeof *vq->avail->ring - 1)) || - (a.used_user_addr & (sizeof *vq->used->ring - 1)) || - (a.log_guest_addr & (sizeof *vq->used->ring - 1))) { + + /* Make sure it's safe to cast pointers to vring types. */ + BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE); + BUILD_BUG_ON(__alignof__ *vq->used > VRING_USED_ALIGN_SIZE); + if ((a.avail_user_addr & (VRING_AVAIL_ALIGN_SIZE - 1)) || + (a.used_user_addr & (VRING_USED_ALIGN_SIZE - 1)) || + (a.log_guest_addr & (sizeof(u64) - 1))) { r = -EINVAL; break; }