On 13.01.25 10:09, Thomas Weißschuh wrote:
On Fri, Jan 10, 2025 at 04:41:03PM +0100, David Hildenbrand wrote:
On 10.01.25 14:05, 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.
Skip the various vvar mappings in virtual_address_range to avoid the issue.
Fixes: e93d2521b27f ("x86/vdso: Split virtual clock pages into dedicated mapping")
Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202412271148.2656e485-lkp@xxxxxxxxx
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
---
tools/testing/selftests/mm/virtual_address_range.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
index 4fc1c21a5e218eaec4d059b75c31a21dd4e8a215..993990aba56fc986c42084ffa91973558aa07e87 100644
--- a/tools/testing/selftests/mm/virtual_address_range.c
+++ b/tools/testing/selftests/mm/virtual_address_range.c
@@ -152,6 +152,10 @@ static int validate_complete_va_space(void)
if (prot[0] != 'r')
continue;
+ /* Only the VDSO can know if a VVAR mapping is really readable */
+ if (vma_name && !strncmp(vma_name, "[vvar", 5))
+ continue;
I'm wondering if there is a more generic way ... but likely not when staring
at /proc/self/maps.
/proc/self/smaps would indicate this as
VM_IO: "io"
VM_DONTDUMP: "dd"
VM_PFNMAP: "pf"
Especially checking for VM_IO sounds reasonable ...
Agreed.
Can we instead rely on madvise(MADV_DOFORK) returning EINVAL iff VM_IO?
That might be one option indeed, although it feels like this is
something that might change in the future ... not sure.
MADV_POPULATE_READ fails with -EFAULT on VM_IO, but also on VM_PFNMAP
and some other conditions, and might not be completely what we want.
We do have some initial smaps parsing in vm_util.c:__check_huge(), maybe
that could be factored out / reused, not sure how hard that would be to
extend to return the flags.
--
Cheers,
David / dhildenb
