Re: [PATCH v3] e1000e: using bottom half to send packets

[P J P <ppandit@redhat.com>]

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+-- On Wed, 22 Jul 2020, Jason Wang wrote --+
| On 2020/7/21 下午11:17, 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.
| >
| > Reported-by: Alexander Bulekov <alxndr@bu.edu>
| > Signed-off-by: Li Qiang <liq3ea@163.com>
| > ---
| > Change since v2:
| > 1. Add comments for the tx bh schdule when VM resumes
| > 2. Leave the set ics code in 'e1000e_start_xmit'
| > 3. Cancel the tx bh and reset tx_waiting in e1000e_core_reset
| 
| 
| So based on our discussion this is probably not sufficient. It solves the
| issue TX re-entrancy but not RX (e.g RX DMA to RDT?) Or is e1000e's RX is
| reentrant?

Fixes: (CVE-2020-15859) -> https://bugzilla.redhat.com/show_bug.cgi?id=1859168

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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