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Re: [Qemu-devel] [PATCH] net: e1000e: fix an infinite loop issue
From: |
Dmitry Fleytman |
Subject: |
Re: [Qemu-devel] [PATCH] net: e1000e: fix an infinite loop issue |
Date: |
Wed, 8 Feb 2017 12:01:32 +0200 |
> On 8 Feb 2017, at 11:30 AM, Li Qiang <address@hidden> wrote:
>
> Hello,
>
> 2017-02-08 16:38 GMT+08:00 Dmitry Fleytman <address@hidden
> <mailto:address@hidden>>:
> Hello,
>
> Thanks for the patch!
>
> The problem of infinite loop indeed exists in e1000e, however it is different
> from the one fixed in e1000.
> Please find my comments inline.
>
>
> If I read the code correctly, I think this issue is the same. Could you
> please explain more? Thanks.
I meant that code changes needed to fix it are slightly different.
>
> ~Dmitry
>
> > On 7 Feb 2017, at 11:43 AM, Li Qiang <address@hidden
> > <mailto:address@hidden>> wrote:
> >
> > From: Li Qiang <address@hidden <mailto:address@hidden>>
> >
> > This issue is the same as e1000 network card in this commit:
> > e1000: eliminate infinite loops on out-of-bounds transfer start.
> >
> > Signed-off-by: Li Qiang <address@hidden <mailto:address@hidden>>
> > ---
> > hw/net/e1000e_core.c | 17 ++++++++++++++++-
> > 1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c
> > index 2b11499..53f2b1d 100644
> > --- a/hw/net/e1000e_core.c
> > +++ b/hw/net/e1000e_core.c
> > @@ -914,7 +914,8 @@ 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;
> > + }
>
> Part of this validity check, namely
> tdh_start >= core->mac[txi->dlen] / E1000_RING_DESC_LEN)
> already done by e1000e_ring_advance(), therefore not needed here.
>
>
> e1000e_ring_advance() check the added r->dh. Not the original one.
Oh, I see now. Right, it does not make sense to check for wraparound in case
original TDH was out of bounds.
Now I see there is one more problem - in case TDH is out of the ring,
e1000e_ring_head_descr()
called from e1000e_start_xmit() will do out of bounds read, so TDH should be
validated prior to
reading the descriptor as well.
Similar problem exists on RX also.
Besides that, as I see now, e1000e_ring_empty() is not called on RX
so validation should be done separately for TX and RX rings.
A function like e1000e_ring_validate() is needed...
>
> The second part - full wraparound protection is relevant, but it fixes more
> symptoms than the cause.
> The only possible cause for full wraparound is r->dt (tail) value bigger or
> equal to r->dlen (length),
> so I would suggest to check for this in e1000e_ring_empty() and cover both TX
> and RX cases at once.
>
>
> Do you mean 'core->mac[r->dt] >= core->mac[r->dlen]' indicate an empty ring?
>
> > }
> >
> > 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];
> > @@ -1605,6 +1616,10 @@ 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;
> > + }
> > } while (desc_offset < total_size);
> >
> > e1000e_update_rx_stats(core, size, total_size);
> > --
> > 1.8.3.1
> >