On Mon, 2011-12-19 at 16:14 -0800, Kees Cook wrote:
On Mon, Dec 19, 2011 at 4:09 PM, Ben Hutchings ben@decadent.org.uk wrote:
Kees, in commit 01e2f533a234dc62d16c0d3d4fb9d71cf1ce50c3 ("drm: do not leak kernel addresses via /proc/dri/*/vma") you changed the logging of high_memory:
seq_printf(m, "vma use count: %d, high_memory = %p, 0x%08llx\n",
seq_printf(m, "vma use count: %d, high_memory = %pK, 0x%pK\n", atomic_read(&dev->vma_count),
high_memory, (u64)virt_to_phys(high_memory));
high_memory, (void *)virt_to_phys(high_memory));This doesn't make sense because the physical address may be truncated (in theory at least).
Leaking even a truncated address is still a problem, IMO. Or do you mean there is some side-effect causing a problem?
I mean that this the conversion to void * can be a narrowing conversion, so when printing of kernel pointers is enabled the full physical address may not be displayed.
I think it would make more sense to make this entire file readable by root only, but I don't know whether anything depends on being able to read it. Its existence is conditional on DRM_DEBUG_CODE != 0 but that is always true at the moment.
The kptr_restrict syscall (that controls %pK behavior) has 3 modes, including one that hides these values even from the root user, so I would prefer this stays as-is.
Sorry I'm being dense, but what problem is %pK causing here? I'd be happy to help get it fixed.
The problem is that it is not suitable for printing physical addresses, because they are not pointers.
Ben.