Messages in this thread | | | From | Alexander Shishkin <> | Subject | Re: [PATCH v1 2/6] virtio console: Harden port adding | Date | Fri, 27 Jan 2023 13:55:43 +0200 |
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"Michael S. Tsirkin" <mst@redhat.com> writes:
> On Thu, Jan 19, 2023 at 10:13:18PM +0200, Alexander Shishkin wrote: >> When handling control messages, instead of peeking at the device memory >> to obtain bits of the control structure, > > Except the message makes it seem that we are getting data from > device memory, when we do nothing of the kind.
We can be, see below.
>> take a snapshot of it once and >> use it instead, to prevent it from changing under us. This avoids races >> between port id validation and control event decoding, which can lead >> to, for example, a NULL dereference in port removal of a nonexistent >> port. >> >> The control structure is small enough (8 bytes) that it can be cached >> directly on the stack. > > I still have no real idea why we want a copy here. > If device can poke anywhere at memory then it can crash kernel anyway. > If there's a bounce buffer or an iommu or some other protection > in place, then this memory can no longer change by the time > we look at it.
We can have shared pages between the host and guest without bounce buffers in between, so they can be both looking directly at the same page.
Regards, -- Alex
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