Re: [RFC PATCH 17/17] virtio_ring: Add validation for used length

[Jason Wang <jasowang@redhat.com>]

在 2021/5/18 上午7:39, Michael S. Tsirkin 写道:
> On Mon, May 17, 2021 at 05:08:36PM +0800, Xie Yongji wrote:
>> This adds validation for used length (might come
>> from an untrusted device) when it will be used by
>> virtio device driver.
>>
>> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
>> ---
>>   drivers/virtio/virtio_ring.c | 22 +++++++++++++++++++---
>>   1 file changed, 19 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index d999a1d6d271..7d4845d06f21 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -68,11 +68,13 @@
>>   struct vring_desc_state_split {
>>   	void *data;			/* Data for callback. */
>>   	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
>> +	u32 in_len;			/* Total length of writable buffer */
>>   };
>>   
>>   struct vring_desc_state_packed {
>>   	void *data;			/* Data for callback. */
>>   	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
>> +	u32 in_len;			/* Total length of writable buffer */
>>   	u16 num;			/* Descriptor list length. */
>>   	u16 last;			/* The last desc state in a list. */
>>   };
>
> Hmm for packed it's aligned to 64 bit anyway, so we are not making it
> any worse. But for split this pushes struct size up by 1/3 increasing
> cache pressure.


We can eliminate this by validating through virtio device driver instead 
of virtio core.

E.g for virtio-net we know the rx buffer size so there's no need to 
store in twice in the core.

Thanks


>
>
>> @@ -486,7 +488,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>>   	struct vring_virtqueue *vq = to_vvq(_vq);
>>   	struct scatterlist *sg;
>>   	struct vring_desc *desc;
>> -	unsigned int i, n, avail, descs_used, prev, err_idx;
>> +	unsigned int i, n, avail, descs_used, prev, err_idx, in_len = 0;
>>   	int head;
>>   	bool indirect;
>>   
>> @@ -570,6 +572,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>>   						     VRING_DESC_F_NEXT |
>>   						     VRING_DESC_F_WRITE,
>>   						     indirect);
>> +			in_len += sg->length;
>>   		}
>>   	}
>>   	/* Last one doesn't continue. */
>> @@ -604,6 +607,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>>   
>>   	/* Store token and indirect buffer state. */
>>   	vq->split.desc_state[head].data = data;
>> +	vq->split.desc_state[head].in_len = in_len;
>>   	if (indirect)
>>   		vq->split.desc_state[head].indir_desc = desc;
>>   	else
>> @@ -784,6 +788,10 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
>>   		BAD_RING(vq, "id %u is not a head!\n", i);
>>   		return NULL;
>>   	}
>> +	if (unlikely(len && vq->split.desc_state[i].in_len < *len)) {
>> +		BAD_RING(vq, "id %u has invalid length: %u!\n", i, *len);
>> +		return NULL;
>> +	}
>>   
>>   	/* detach_buf_split clears data, so grab it now. */
>>   	ret = vq->split.desc_state[i].data;
>> @@ -1059,7 +1067,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>>   {
>>   	struct vring_packed_desc *desc;
>>   	struct scatterlist *sg;
>> -	unsigned int i, n, err_idx;
>> +	unsigned int i, n, err_idx, in_len = 0;
>>   	u16 head, id;
>>   	dma_addr_t addr;
>>   
>> @@ -1084,6 +1092,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>>   			if (vring_mapping_error(vq, addr))
>>   				goto unmap_release;
>>   
>> +			in_len += (n < out_sgs) ? 0 : sg->length;
>>   			desc[i].flags = cpu_to_le16(n < out_sgs ?
>>   						0 : VRING_DESC_F_WRITE);
>>   			desc[i].addr = cpu_to_le64(addr);
>> @@ -1141,6 +1150,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>>   	vq->packed.desc_state[id].data = data;
>>   	vq->packed.desc_state[id].indir_desc = desc;
>>   	vq->packed.desc_state[id].last = id;
>> +	vq->packed.desc_state[id].in_len = in_len;
>>   
>>   	vq->num_added += 1;
>>   
>> @@ -1173,7 +1183,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>>   	struct vring_virtqueue *vq = to_vvq(_vq);
>>   	struct vring_packed_desc *desc;
>>   	struct scatterlist *sg;
>> -	unsigned int i, n, c, descs_used, err_idx;
>> +	unsigned int i, n, c, descs_used, err_idx, in_len = 0;
>>   	__le16 head_flags, flags;
>>   	u16 head, id, prev, curr, avail_used_flags;
>>   
>> @@ -1223,6 +1233,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>>   			if (vring_mapping_error(vq, addr))
>>   				goto unmap_release;
>>   
>> +			in_len += (n < out_sgs) ? 0 : sg->length;
>>   			flags = cpu_to_le16(vq->packed.avail_used_flags |
>>   				    (++c == total_sg ? 0 : VRING_DESC_F_NEXT) |
>>   				    (n < out_sgs ? 0 : VRING_DESC_F_WRITE));
>> @@ -1268,6 +1279,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>>   	vq->packed.desc_state[id].data = data;
>>   	vq->packed.desc_state[id].indir_desc = ctx;
>>   	vq->packed.desc_state[id].last = prev;
>> +	vq->packed.desc_state[id].in_len = in_len;
>>   
>>   	/*
>>   	 * A driver MUST NOT make the first descriptor in the list
>> @@ -1456,6 +1468,10 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
>>   		BAD_RING(vq, "id %u is not a head!\n", id);
>>   		return NULL;
>>   	}
>> +	if (unlikely(len && vq->packed.desc_state[id].in_len < *len)) {
>> +		BAD_RING(vq, "id %u has invalid length: %u!\n", id, *len);
>> +		return NULL;
>> +	}
>>   
>>   	/* detach_buf_packed clears data, so grab it now. */
>>   	ret = vq->packed.desc_state[id].data;
>> -- 
>> 2.11.0