Re: [PATCH] kni: fix possible kernel crash with va2pa

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 2/28/2019 7:30 AM, Yangchao Zhou wrote:
> va2pa depends on the physical address and virtual address offset of
> current mbuf. It may get the wrong physical address of next mbuf which
> allocated in another hugepage segment.

Hi Yangchao,

The problem you described seems valid, when current mbuf and the mbuf pointed bu
next pointer from different (huge)pages, address calculation will be wrong.

Can you able to reproduce the issue, or recognized the problem theoretically?

> 
> Signed-off-by: Yangchao Zhou <zhouyates@gmail.com>
> ---
>  kernel/linux/kni/kni_net.c                       | 16 ++--------------
>  .../eal/include/exec-env/rte_kni_common.h        |  4 ++++
>  lib/librte_kni/rte_kni.c                         | 15 ++++++++++++++-
>  3 files changed, 20 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/linux/kni/kni_net.c b/kernel/linux/kni/kni_net.c
> index 7371b6d58..caef8754f 100644
> --- a/kernel/linux/kni/kni_net.c
> +++ b/kernel/linux/kni/kni_net.c
> @@ -61,18 +61,6 @@ kva2data_kva(struct rte_kni_mbuf *m)
>  	return phys_to_virt(m->buf_physaddr + m->data_off);
>  }
>  
> -/* virtual address to physical address */
> -static void *
> -va2pa(void *va, struct rte_kni_mbuf *m)
> -{
> -	void *pa;
> -
> -	pa = (void *)((unsigned long)va -
> -			((unsigned long)m->buf_addr -
> -			 (unsigned long)m->buf_physaddr));
> -	return pa;
> -}
> -
>  /*
>   * It can be called to process the request.
>   */
> @@ -363,7 +351,7 @@ kni_net_rx_normal(struct kni_dev *kni)
>  				if (!kva->next)
>  					break;
>  
> -				kva = pa2kva(va2pa(kva->next, kva));
> +				kva = pa2kva(kva->next_pa);
>  				data_kva = kva2data_kva(kva);
>  			}
>  		}
> @@ -545,7 +533,7 @@ kni_net_rx_lo_fifo_skb(struct kni_dev *kni)
>  				if (!kva->next)
>  					break;
>  
> -				kva = pa2kva(va2pa(kva->next, kva));
> +				kva = pa2kva(kva->next_pa);
>  				data_kva = kva2data_kva(kva);
>  			}
>  		}
> diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> index 5afa08713..608f5c13f 100644
> --- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> +++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> @@ -87,6 +87,10 @@ struct rte_kni_mbuf {
>  	char pad3[8] __attribute__((__aligned__(RTE_CACHE_LINE_MIN_SIZE)));
>  	void *pool;
>  	void *next;
> +	union {
> +		uint64_t tx_offload;
> +		void *next_pa;      /**< Physical address of next mbuf. */
> +	};

This will cause overwrite the 'tx_offload' via 'next_pa', we don't use
tx_offload in KNI but not sure about removing potential use for future.

What do you think about converting 'm->next' to physical address before putting
them into 'rx_q', and in kernel side after data copied to skb convert 'm->next'
back to virtual address before putting it into 'free_q' ?
I think both address conversion can be possible to do, a little tricky because
address conversion should be calculated in next mbuf and previous mbuf->next in
the chain should be updated.

>  };
>  
>  /*
> diff --git a/lib/librte_kni/rte_kni.c b/lib/librte_kni/rte_kni.c
> index 73aeccccf..1aaebcfa1 100644
> --- a/lib/librte_kni/rte_kni.c
> +++ b/lib/librte_kni/rte_kni.c
> @@ -353,6 +353,17 @@ va2pa(struct rte_mbuf *m)
>  			 (unsigned long)m->buf_iova));
>  }
>  
> +static void *
> +va2pa_all(struct rte_mbuf *m)
> +{
> +	struct rte_kni_mbuf *mbuf = (struct rte_kni_mbuf *)m;
> +	while (mbuf->next) {
> +		mbuf->next_pa = va2pa(mbuf->next);
> +		mbuf = mbuf->next;
> +	}
> +	return va2pa(m);
> +}
> +
>  static void
>  obj_free(struct rte_mempool *mp __rte_unused, void *opaque, void *obj,
>  		unsigned obj_idx __rte_unused)
> @@ -550,7 +561,7 @@ rte_kni_tx_burst(struct rte_kni *kni, struct rte_mbuf **mbufs, unsigned num)
>  	unsigned int i;
>  
>  	for (i = 0; i < num; i++)
> -		phy_mbufs[i] = va2pa(mbufs[i]);
> +		phy_mbufs[i] = va2pa_all(mbufs[i]);
>  
>  	ret = kni_fifo_put(kni->rx_q, phy_mbufs, num);
>  
> @@ -607,6 +618,8 @@ kni_allocate_mbufs(struct rte_kni *kni)
>  			 offsetof(struct rte_kni_mbuf, pkt_len));
>  	RTE_BUILD_BUG_ON(offsetof(struct rte_mbuf, ol_flags) !=
>  			 offsetof(struct rte_kni_mbuf, ol_flags));
> +	RTE_BUILD_BUG_ON(offsetof(struct rte_mbuf, tx_offload) !=
> +			 offsetof(struct rte_kni_mbuf, tx_offload));
>  
>  	/* Check if pktmbuf pool has been configured */
>  	if (kni->pktmbuf_pool == NULL) {
>