Re: [kernel-hardening] [PATCH 09/38] usercopy: Mark kmalloc caches as usercopy caches

Christian Borntraeger
2020-01-29T17:20:27Z

On 29.01.20 18:09, Christoph Hellwig wrote:
> On Wed, Jan 29, 2020 at 06:07:14PM +0100, Christian Borntraeger wrote:
>>> DMA can be done to NORMAL memory as well.
>>
>> Exactly.
>> I think iucv uses GFP_DMA because z/VM needs those buffers to reside below 2GB (which is ZONA_DMA for s390).
>
> The normal way to allocate memory with addressing limits would be to
> use dma_alloc_coherent and friends. Any chance to switch iucv over to
> that? Or is there no device associated with it?

There is not necessarily a device for that. It is a hypervisor interface (an
instruction that is interpreted by z/VM). We do have the netiucv driver that
creates a virtual nic, but there is also AF_IUCV which works without a device.

But back to the original question: If we mark kmalloc caches as usercopy caches,
we should do the same for DMA kmalloc caches. As outlined by Christoph, this has
nothing to do with device DMA.