Re: [Qemu-devel] [PATCH v2] net: e1000e: fix an infinite loop issue

[Dmitry Fleytman]

> On 9 Feb 2017, at 04:11 AM, Li Qiang <address@hidden> wrote:
> 
> From: Li Qiang <address@hidden>
> 
> This issue is like the issue in e1000 network card addressed in
> this commit:
> e1000: eliminate infinite loops on out-of-bounds transfer start.

Hi,

Please see my comments below.

> 
> Signed-off-by: Li Qiang <address@hidden>
> ---
> 
> Changes since v1:
> make wraparound detect in e1000e_ring_empty
> 
> hw/net/e1000e_core.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c
> index 2b11499..d4c56c3 100644
> --- a/hw/net/e1000e_core.c
> +++ b/hw/net/e1000e_core.c
> @@ -806,7 +806,8 @@ typedef struct E1000E_RingInfo_st {
> static inline bool
> e1000e_ring_empty(E1000ECore *core, const E1000E_RingInfo *r)
> {
> -    return core->mac[r->dh] == core->mac[r->dt];
> +    return core->mac[r->dh] == core->mac[r->dt] ||
> +                core->mac[r->dt] >= core->mac[r->dlen];

Here r->dt is index while r->dlen is length in bytes,
so r->dlen should be divided by E1000_RING_DESC_LEN

The same way as you do below while checking for wrap around.

> }
> 
> static inline uint64_t
> @@ -914,7 +915,7 @@ e1000e_start_xmit(E1000ECore *core, const E1000E_TxRing 
> *txr)
>     struct e1000_tx_desc desc;
>     bool ide = false;
>     const E1000E_RingInfo *txi = txr->i;
> -    uint32_t cause = E1000_ICS_TXQE;
> +    uint32_t tdh_start = core->mac[txi->dh], cause = E1000_ICS_TXQE;
> 
>     if (!(core->mac[TCTL] & E1000_TCTL_EN)) {
>         trace_e1000e_tx_disabled();
> @@ -933,6 +934,14 @@ e1000e_start_xmit(E1000ECore *core, const E1000E_TxRing 
> *txr)
>         cause |= e1000e_txdesc_writeback(core, base, &desc, &ide, txi->idx);
> 
>         e1000e_ring_advance(core, txi, 1);
> +
> +        /*
> +         * The following avoid infinite loop, just as the e1000
> +         */
> +        if (core->mac[txi->dh] == tdh_start ||
> +            tdh_start >= core->mac[txi->dlen] / E1000_RING_DESC_LEN) {
> +            break;
> +            }

IIUC infinite loop protection already implemented by your changes for 
e1000e_ring_empty()

>     }
> 
>     if (!ide || !e1000e_intrmgr_delay_tx_causes(core, &cause)) {
> @@ -1500,6 +1509,7 @@ e1000e_write_packet_to_guest(E1000ECore *core, struct 
> NetRxPkt *pkt,
>     size_t desc_size;
>     size_t desc_offset = 0;
>     size_t iov_ofs = 0;
> +    uint32_t rdh_start;
> 
>     struct iovec *iov = net_rx_pkt_get_iovec(pkt);
>     size_t size = net_rx_pkt_get_total_len(pkt);
> @@ -1509,6 +1519,7 @@ e1000e_write_packet_to_guest(E1000ECore *core, struct 
> NetRxPkt *pkt,
>     bool do_ps = e1000e_do_ps(core, pkt, &ps_hdr_len);
> 
>     rxi = rxr->i;
> +    rdh_start = core->mac[rxi->dh];
> 
>     do {
>         hwaddr ba[MAX_PS_BUFFERS];
> @@ -1522,6 +1533,10 @@ e1000e_write_packet_to_guest(E1000ECore *core, struct 
> NetRxPkt *pkt,
>             desc_size = core->rx_desc_buf_size;
>         }
> 
> +        if (e1000e_ring_empty(core, rxi)) {
> +            return;
> +        }
> +
>         base = e1000e_ring_head_descr(core, rxi);
> 
>         pci_dma_read(d, base, &desc, core->rx_desc_len);
> @@ -1605,6 +1620,10 @@ e1000e_write_packet_to_guest(E1000ECore *core, struct 
> NetRxPkt *pkt,
>         e1000e_ring_advance(core, rxi,
>                             core->rx_desc_len / E1000_MIN_RX_DESC_LEN);
> 
> +        if (core->mac[rxi->dh] == rdh_start ||
> +            rdh_start >= core->mac[rxi->dlen] / E1000_RING_DESC_LEN) {
> +            break;
> +            }


IIUC, infinite loop protection here is covered by newly introduced call to 
e1000e_ring_empty().

~Dmitry

>     } while (desc_offset < total_size);
> 
>     e1000e_update_rx_stats(core, size, total_size);
> -- 
> 1.8.3.1
>