Re: [PATCH] iommu/dma: Fix MSI reservation allocation

[Marc Zyngier]

On 2020-03-03 17:23, Robin Murphy wrote:
> On 03/03/2020 11:51 am, Marc Zyngier wrote:
> > The way cookie_init_hw_msi_region() allocates the iommu_dma_msi_page
> > structures doesn't match the way iommu_put_dma_cookie() frees them.
> >
> > The former performs a single allocation of all the required 
> > structures,
> > while the latter tries to free them one at a time. It doesn't quite
> > work for the main use case (the GICv3 ITS where the range is 64kB)
> > when the base ganule size is 4kB.
> >
> > This leads to a nice slab corruption on teardown, which is easily
> > observable by simply creating a VF on a SRIOV-capable device, and
> > tearing it down immediately (no need to even make use of it).
> >
> > Fix it by allocating iommu_dma_msi_page structures one at a time.
>
> Bleh, you know you're supposed to be using 64K pages on those things, 
> right? :P

lalalala... ;-)

[...]

> > +		if (!msi_page) {
> > +			ret = -ENOMEM;
>
> I think we can just return here and skip the cleanup below - by the
> time we get here the cookie itself has already been allocated and
> initialised, so even if iommu_dma_init_domain() fails someone else has
> already accepted the responsibility of calling iommu_put_dma_cookie()
> at some point later, which will clean up properly.

Ah, that's a very good point. I'll refresh the patch with a simplified
error handling.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...