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.
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