On 14.01.25 17:06, Thomas Weißschuh wrote:
The virtual_address_range selftest reads from the start of each mapping
listed in /proc/self/maps.
However not all mappings are valid to be arbitrarily accessed.
For example the vvar data used for virtual clocks on x86 [vvar_vclock]
can only be accessed if 1) the kernel configuration enables virtual
clocks and 2) the hypervisor provided the data for it.
Only the VDSO itself has the necessary information to know this.
Since commit e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
the virtual clock data was split out into its own mapping, leading
to EFAULT from read() during the validation.
Check for the VM_IO flag as a proxy.
It is present for the VVAR mappings and MMIO ranges can be dangerous to
access arbitrarily.
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202412271148.2656e485-lkp@xxxxxxxxx
Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/e97c2a5d-c815-4936-a767-ac42a3220a90@xxxxxxxxxx/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Unfortunately, vsyscall doesn't seem to set VM_IO, it only has
VmFlags: ex
Which is rather weird.
So we cannot remove that special-casing right now,
--
Cheers,
David / dhildenb
