Re: [PATCH 1/1] mm/debug_vm_pgtable: fix alignment for pmd/pud_advanced_tests()

From: Anshuman Khandual
Date: Wed May 26 2021 - 08:35:50 EST

On 5/26/21 4:57 PM, Anatoly Pugachev wrote:
> On Tue, May 25, 2021 at 4:03 PM Gerald Schaefer
> <gerald.schaefer@xxxxxxxxxxxxx> wrote:
>> In pmd/pud_advanced_tests(), the vaddr is aligned up to the next pmd/pud
>> entry, and so it does not match the given pmdp/pudp and (aligned down) pfn
>> any more.
>> For s390, this results in memory corruption, because the IDTE instruction
>> used e.g. in xxx_get_and_clear() will take the vaddr for some calculations,
>> in combination with the given pmdp. It will then end up with a wrong table
>> origin, ending on ...ff8, and some of those wrongly set low-order bits will
>> also select a wrong pagetable level for the index addition. IDTE could
>> therefore invalidate (or 0x20) something outside of the page tables,
>> depending on the wrongly picked index, which in turn depends on the random
>> vaddr.
>> As result, we sometimes see "BUG task_struct (Not tainted): Padding
>> overwritten" on s390, where one 0x5a padding value got overwritten with
>> 0x7a.
>> Fix this by aligning down, similar to how the pmd/pud_aligned pfns are
>> calculated.
>> Fixes: a5c3b9ffb0f40 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers")
>> Cc: <stable@xxxxxxxxxxxxxxx> # v5.9+
>> Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> boot tested on sparc64 with quick run of stress-ng ( --class memory
> --sequential -1 --timeout 10s -v --pathological --oomable
> --metrics-brief )
> stress-ng: debug: [371408] system: Linux ttip
> 5.13.0-rc3-00043-gad9f25d33860-dirty #218 SMP Wed May 26 11:55:54 MSK
> 2021 sparc64
> Tested-by: Anatoly Pugachev <matorola@xxxxxxxxx>

spac64 does not enable ARCH_HAS_DEBUG_VM_PGTABLE, did you enable it
before running the test ? Did the entire test debug_vm_pgtable() run
successfully on sparc64 ?