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| From: | Jason Wang |
| Subject: | Re: [PATCH] e1000e: using bottom half to send packets |
| Date: | Mon, 20 Jul 2020 11:59:48 +0800 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
On 2020/7/17 下午11:46, Li Qiang wrote:
Jason Wang <jasowang@redhat.com> 于2020年7月17日周五 下午1:39写道：On 2020/7/17 下午12:46, Li Qiang wrote:Jason Wang <jasowang@redhat.com> 于2020年7月17日周五 上午11:10写道：On 2020/7/17 上午12:14, 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.'I think several things were missed in this patch (take virtio-net as a reference), do we need the following things:Thanks Jason, In fact I know this, I'm scared for touching this but I want to try. Thanks for your advice.- Cancel the bh when VM is stopped.Ok. I think add a vm state change notifier for e1000e can address this.- A throttle to prevent bh from executing too much timer?Ok, I think add a config timeout and add a timer in e1000e can address this.Sorry, a typo. I meant we probably need a tx_burst as what virtio-net did.- A flag to record whether or not this a pending tx (and migrate it?)Is just a flag enough? Could you explain more about the idea behind processing the virtio-net/e1000e using bh like this?Virtio-net use a tx_waiting variable to record whether or not there's a pending bh. (E.g bh is cancelled due to vmstop, we need reschedule it after vmresume). Maybe we can do something simpler by just schecule bh unconditionally during vm resuming.For example, if the guest trigger a lot of packets send and if the bh is scheduled in IO thread. So will we lost packets?We don't since we don't populate virtqueue which means packets are queued there.This remind of me a question: If we use tx_burst like in virtion-net. For detail: If we sent out 'tx_burst' packets per bh. Then we set 'tx_waiting' and then schedule another bh. However if between two bh schedule, the guest change the e1000e register such 'r->dh' 'r->dlen'. The data is fully corrupted. In fact this issue does exist in my origin patch. That's What if following happend: vcpu thread: guest write e1000e MMIO to trigger packets send vcpu thread: schedule a bh vcpu thread: return IO thread: begin to run the bh and start send packets vcpu thread: write register again such as 'r->dh' 'r->dlen'.. So here the IO thread and vcpu thread will race the register? If I remember correctly, the virtio net has no such problem because it uses ring buffer and the backedn(virtio device) uses the shadow index to index the ring buffer data. What's your idea here?
I think we serialize them through bql? (qemu_mutex_lock_iothread()) Thanks
Thanks, Li QiangThanksHow we avoid this in virtio-net. Thanks, Li QiangThanksThis patch fixes this UAF. Signed-off-by: Li Qiang <liq3ea@163.com> --- hw/net/e1000e_core.c | 25 +++++++++++++++++-------- hw/net/e1000e_core.h | 2 ++ 2 files changed, 19 insertions(+), 8 deletions(-) diff --git a/hw/net/e1000e_core.c b/hw/net/e1000e_core.c index bcd186cac5..6165b04b68 100644 --- a/hw/net/e1000e_core.c +++ b/hw/net/e1000e_core.c @@ -2423,32 +2423,27 @@ 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); + 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); + 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); } } @@ -3322,6 +3317,16 @@ e1000e_vm_state_change(void *opaque, int running, RunState state) } } +static void e1000e_core_tx_bh(void *opaque) +{ + struct e1000e_tx *tx = opaque; + E1000ECore *core = tx->core; + E1000E_TxRing txr; + + e1000e_tx_ring_init(core, &txr, tx - &core->tx[0]); + e1000e_start_xmit(core, &txr); +} + void e1000e_core_pci_realize(E1000ECore *core, const uint16_t *eeprom_templ, @@ -3340,6 +3345,8 @@ e1000e_core_pci_realize(E1000ECore *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 +3374,8 @@ 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_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..94ddc6afc2 100644 --- a/hw/net/e1000e_core.h +++ b/hw/net/e1000e_core.h @@ -77,6 +77,8 @@ struct E1000Core { unsigned char sum_needed; bool cptse; struct NetTxPkt *tx_pkt; + QEMUBH *tx_bh; + E1000ECore *core; } tx[E1000E_NUM_QUEUES]; struct NetRxPkt *rx_pkt;
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