Re: [PATCH v2] e1000e: using bottom half to send packets

[Li Qiang]

Jason Wang <jasowang@redhat.com> 于2020年7月21日周二 上午10:03写道：
>
>
> On 2020/7/21 上午12:45, Li Qiang wrote:
> > Alexander Bulekov reported a UAF bug related e1000e packets send.
> >
> > -->https://bugs.launchpad.net/qemu/+bug/1886362
> >
> > This is because the guest trigger a e1000e packet send and set the
> > data's address to e1000e's MMIO address. So when the e1000e do DMA
> > it will write the MMIO again and trigger re-entrancy and finally
> > causes this UAF.
> >
> > Paolo suggested to use a bottom half whenever MMIO is doing complicate
> > things in here:
> > -->https://lists.nongnu.org/archive/html/qemu-devel/2020-07/msg03342.html
> >
> > Reference here:
> > 'The easiest solution is to delay processing of descriptors to a bottom
> > half whenever MMIO is doing something complicated.  This is also better
> > for latency because it will free the vCPU thread more quickly and leave
> > the work to the I/O thread.'
> >
> > This patch fixes this UAF.
> >
> > Signed-off-by: Li Qiang <liq3ea@163.com>
> > ---
> > Change since v1:
> > Per Jason's review here:
> > -- https://lists.nongnu.org/archive/html/qemu-devel/2020-07/msg05368.html
> > 1. Cancel and schedule the tx bh when VM is stopped or resume
> > 2. Add a tx_burst for e1000e configuration to throttle the bh execution
> > 3. Add a tx_waiting to record whether the bh is pending or not
> > Don't use BQL in the tx_bh handler as when tx_bh is executed, the BQL is
> > acquired.
> >
> >   hw/net/e1000e.c      |   6 +++
> >   hw/net/e1000e_core.c | 106 ++++++++++++++++++++++++++++++++++---------
> >   hw/net/e1000e_core.h |   8 ++++
> >   3 files changed, 98 insertions(+), 22 deletions(-)
> >
> > diff --git a/hw/net/e1000e.c b/hw/net/e1000e.c
> > index fda34518c9..24e35a78bf 100644
> > --- a/hw/net/e1000e.c
> > +++ b/hw/net/e1000e.c
> > @@ -77,10 +77,14 @@ typedef struct E1000EState {
> >
> >       bool disable_vnet;
> >
> > +    int32_t tx_burst;
> > +
> >       E1000ECore core;
> >
> >   } E1000EState;
> >
> > +#define TX_BURST 256
> > +
> >   #define E1000E_MMIO_IDX     0
> >   #define E1000E_FLASH_IDX    1
> >   #define E1000E_IO_IDX       2
> > @@ -263,6 +267,7 @@ static void e1000e_core_realize(E1000EState *s)
> >   {
> >       s->core.owner = &s->parent_obj;
> >       s->core.owner_nic = s->nic;
> > +    s->core.tx_burst = s->tx_burst;
> >   }
> >
> >   static void
> > @@ -665,6 +670,7 @@ static Property e1000e_properties[] = {
> >                           e1000e_prop_subsys_ven, uint16_t),
> >       DEFINE_PROP_SIGNED("subsys", E1000EState, subsys, 0,
> >                           e1000e_prop_subsys, uint16_t),
> > +    DEFINE_PROP_INT32("x-txburst", E1000EState, tx_burst, TX_BURST),
> >       DEFINE_PROP_END_OF_LIST(),
> >   };
> >
> > diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c
> > index bcd186cac5..0a38a50cca 100644
> > --- a/hw/net/e1000e_core.c
> > +++ b/hw/net/e1000e_core.c
> > @@ -909,19 +909,18 @@ e1000e_rx_ring_init(E1000ECore *core, E1000E_RxRing 
> > *rxr, int idx)
> >       rxr->i      = &i[idx];
> >   }
> >
> > -static void
> > -e1000e_start_xmit(E1000ECore *core, const E1000E_TxRing *txr)
> > +static int32_t
> > +e1000e_start_xmit(struct e1000e_tx *q)
> >   {
> > +    E1000ECore *core = q->core;
> >       dma_addr_t base;
> >       struct e1000_tx_desc desc;
> > -    bool ide = false;
> > -    const E1000E_RingInfo *txi = txr->i;
> > -    uint32_t cause = E1000_ICS_TXQE;
> > +    const E1000E_RingInfo *txi;
> > +    E1000E_TxRing txr;
> > +    int32_t num_packets = 0;
> >
> > -    if (!(core->mac[TCTL] & E1000_TCTL_EN)) {
> > -        trace_e1000e_tx_disabled();
> > -        return;
> > -    }
> > +    e1000e_tx_ring_init(core, &txr, q - &core->tx[0]);
> > +    txi = txr.i;
> >
> >       while (!e1000e_ring_empty(core, txi)) {
> >           base = e1000e_ring_head_descr(core, txi);
> > @@ -931,15 +930,17 @@ e1000e_start_xmit(E1000ECore *core, const 
> > E1000E_TxRing *txr)
> >           trace_e1000e_tx_descr((void *)(intptr_t)desc.buffer_addr,
> >                                 desc.lower.data, desc.upper.data);
> >
> > -        e1000e_process_tx_desc(core, txr->tx, &desc, txi->idx);
> > -        cause |= e1000e_txdesc_writeback(core, base, &desc, &ide, 
> > txi->idx);
> > +        e1000e_process_tx_desc(core, txr.tx, &desc, txi->idx);
> > +        q->cause |= e1000e_txdesc_writeback(core, base, &desc,
> > +                                            &q->ide, txi->idx);
> >
> >           e1000e_ring_advance(core, txi, 1);
> > +        if (++num_packets >= core->tx_burst) {
> > +            break;
> > +        }
> >       }
> >
> > -    if (!ide || !e1000e_intrmgr_delay_tx_causes(core, &cause)) {
> > -        e1000e_set_interrupt_cause(core, cause);
> > -    }
> > +    return num_packets;
> >   }
> >
> >   static bool
> > @@ -2423,32 +2424,41 @@ e1000e_set_dbal(E1000ECore *core, int index, 
> > uint32_t val)
> >   static void
> >   e1000e_set_tctl(E1000ECore *core, int index, uint32_t val)
> >   {
> > -    E1000E_TxRing txr;
> >       core->mac[index] = val;
> >
> >       if (core->mac[TARC0] & E1000_TARC_ENABLE) {
> > -        e1000e_tx_ring_init(core, &txr, 0);
> > -        e1000e_start_xmit(core, &txr);
> > +        if (core->tx[0].tx_waiting) {
> > +            return;
> > +        }
> > +        core->tx[0].tx_waiting = 1;
> > +        if (!core->vm_running) {
> > +            return;
> > +        }
> > +        qemu_bh_schedule(core->tx[0].tx_bh);
> >       }
> >
> >       if (core->mac[TARC1] & E1000_TARC_ENABLE) {
> > -        e1000e_tx_ring_init(core, &txr, 1);
> > -        e1000e_start_xmit(core, &txr);
> > +        if (core->tx[1].tx_waiting) {
> > +            return;
> > +        }
> > +        core->tx[1].tx_waiting = 1;
> > +        if (!core->vm_running) {
> > +            return;
> > +        }
> > +        qemu_bh_schedule(core->tx[1].tx_bh);
> >       }
> >   }
> >
> >   static void
> >   e1000e_set_tdt(E1000ECore *core, int index, uint32_t val)
> >   {
> > -    E1000E_TxRing txr;
> >       int qidx = e1000e_mq_queue_idx(TDT, index);
> >       uint32_t tarc_reg = (qidx == 0) ? TARC0 : TARC1;
> >
> >       core->mac[index] = val & 0xffff;
> >
> >       if (core->mac[tarc_reg] & E1000_TARC_ENABLE) {
> > -        e1000e_tx_ring_init(core, &txr, qidx);
> > -        e1000e_start_xmit(core, &txr);
> > +        qemu_bh_schedule(core->tx[qidx].tx_bh);
> >       }
> >   }
> >
> > @@ -3315,10 +3325,56 @@ e1000e_vm_state_change(void *opaque, int running, 
> > RunState state)
> >           trace_e1000e_vm_state_running();
> >           e1000e_intrmgr_resume(core);
> >           e1000e_autoneg_resume(core);
> > +        core->vm_running = 1;
> > +
> > +        for (int i = 0; i < E1000E_NUM_QUEUES; i++) {
> > +            qemu_bh_schedule(core->tx[i].tx_bh);
>
>
> I guess the reason for the unconditional scheduling of bh is to make
> sure tx work after live migration since we don't migrate tx_waiting.
>
> If yes, better add a comment here.

Ok will do in next revision.

And do we need to clear tx_waiting here?

I think there is no need as the tx_bh handler will do this.

>
>
> > +        }
> > +
> >       } else {
> >           trace_e1000e_vm_state_stopped();
> > +
> > +        for (int i = 0; i < E1000E_NUM_QUEUES; i++) {
> > +            qemu_bh_cancel(core->tx[i].tx_bh);
> > +        }
> > +
> >           e1000e_autoneg_pause(core);
> >           e1000e_intrmgr_pause(core);
> > +        core->vm_running = 0;
> > +    }
> > +}
> > +
> > +
> > +static void e1000e_core_tx_bh(void *opaque)
> > +{
> > +    struct e1000e_tx *q = opaque;
> > +    E1000ECore *core = q->core;
> > +    int32_t ret;
> > +
> > +    if (!core->vm_running) {
> > +        assert(q->tx_waiting);
> > +        return;
> > +    }
> > +
> > +    q->tx_waiting = 0;
> > +
> > +    if (!(core->mac[TCTL] & E1000_TCTL_EN)) {
> > +        trace_e1000e_tx_disabled();
> > +        return;
> > +    }
> > +
> > +    q->cause = E1000_ICS_TXQE;
> > +    q->ide = false;
> > +
> > +    ret = e1000e_start_xmit(q);
> > +    if (ret >= core->tx_burst) {
> > +        qemu_bh_schedule(q->tx_bh);
> > +        q->tx_waiting = 1;
> > +        return;
> > +    }
> > +
> > +    if (!q->ide || !e1000e_intrmgr_delay_tx_causes(core, &q->cause)) {
> > +        e1000e_set_interrupt_cause(core, q->cause);
>
>
> So I think this will cause some delay of the interrupt delivering.

Exactly. if tx burst occurs, the interrupt won't be triggered in the
first tx_bh handler.
As we give the vcpu more time and this may acceptable?

It
> looks to be it's better to leave the set ics in e1000e_start_xmit().

I think let e1000e_start_xmit just send packets is more clean.
Leave setting ics in it will not improve the performance as far as I can see.
What's your idea here to leave it in e1000e_start_xmit?

>
>
> >       }
> >   }
> >
> > @@ -3334,12 +3390,15 @@ e1000e_core_pci_realize(E1000ECore     *core,
> >                                          e1000e_autoneg_timer, core);
> >       e1000e_intrmgr_pci_realize(core);
> >
> > +    core->vm_running = runstate_is_running();
> >       core->vmstate =
> >           qemu_add_vm_change_state_handler(e1000e_vm_state_change, core);
> >
> >       for (i = 0; i < E1000E_NUM_QUEUES; i++) {
> >           net_tx_pkt_init(&core->tx[i].tx_pkt, core->owner,
> >                           E1000E_MAX_TX_FRAGS, core->has_vnet);
> > +        core->tx[i].core = core;
> > +        core->tx[i].tx_bh = qemu_bh_new(e1000e_core_tx_bh, &core->tx[i]);
> >       }
> >
> >       net_rx_pkt_init(&core->rx_pkt, core->has_vnet);
> > @@ -3367,6 +3426,9 @@ e1000e_core_pci_uninit(E1000ECore *core)
> >       for (i = 0; i < E1000E_NUM_QUEUES; i++) {
> >           net_tx_pkt_reset(core->tx[i].tx_pkt);
> >           net_tx_pkt_uninit(core->tx[i].tx_pkt);
> > +        qemu_bh_cancel(core->tx[i].tx_bh);
> > +        qemu_bh_delete(core->tx[i].tx_bh);
> > +        core->tx[i].tx_bh = NULL;
> >       }
> >
> >       net_rx_pkt_uninit(core->rx_pkt);
> > diff --git a/hw/net/e1000e_core.h b/hw/net/e1000e_core.h
> > index aee32f7e48..0c16dce3a6 100644
> > --- a/hw/net/e1000e_core.h
> > +++ b/hw/net/e1000e_core.h
> > @@ -77,10 +77,18 @@ struct E1000Core {
> >           unsigned char sum_needed;
> >           bool cptse;
> >           struct NetTxPkt *tx_pkt;
> > +        QEMUBH *tx_bh;
> > +        uint32_t tx_waiting;
> > +        uint32_t cause;
> > +        bool ide;
> > +        E1000ECore *core;
> >       } tx[E1000E_NUM_QUEUES];
> >
> >       struct NetRxPkt *rx_pkt;
> >
> > +    int32_t tx_burst;
> > +
> > +    bool vm_running;
> >       bool has_vnet;
> >       int max_queue_num;
> >
>
>
> Do we need to cancel the bh and reset tx_waiting in e1000e_core_reset()?

I think we need. But why the virtio net doesn't do this? Maybe it also
lack of this?


Thanks,
Li Qiang

>
> Thanks
>