Re: [PATCH 01/12] iommu/vt-d: Use iommu_get_domain_for_dev() in debugfs

[Robin Murphy]

On 2022-05-31 16:59, Jason Gunthorpe wrote:
> On Tue, May 31, 2022 at 02:52:28PM +0100, Robin Murphy wrote:
>
> > > +                break;
> > > +            pgtable_walk_level(m, phys_to_virt(phys_addr),
> >
> > Also, obligatory reminder that pfn_valid() only means that pfn_to_page()
> > gets you a valid struct page. Whether that page is direct-mapped kernel
> > memory or not is a different matter.
>
> Even though this is debugfs, if the operation is sketchy like that and
> can theortically crash the kernel the driver should test capabilities,
> CAP_SYS_RAWIO or something may be appropriate. I don't think we have a
> better cap for 'userspace may crash the kernel'

It shouldn't be insurmountable to make this safe, it just needs a bit 
more than pfn_valid(), which can still return true off the ends of the 
memory map if they're not perfectly section-aligned, and for random 
reserved holes in the middle.

Robin.