From: Gerald Schaefer gerald.schaefer@linux.ibm.com Subject: mm/debug_vm_pgtable: fix alignment for pmd/pud_advanced_tests()

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.

Link: https://lkml.kernel.org/r/20210525130043.186290-2-gerald.schaefer@linux.ibm.... Fixes: a5c3b9ffb0f40 ("mm/debug_vm_pgtable: add tests validating advanced arch page table helpers") Signed-off-by: Gerald Schaefer gerald.schaefer@linux.ibm.com Reviewed-by: Anshuman Khandual anshuman.khandual@arm.com Cc: Vineet Gupta vgupta@synopsys.com Cc: Palmer Dabbelt palmer@dabbelt.com Cc: Paul Walmsley paul.walmsley@sifive.com Cc: stable@vger.kernel.org [5.9+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/debug_vm_pgtable.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/debug_vm_pgtable.c~mm-debug_vm_pgtable-fix-alignment-for-pmd-pud_advanced_tests +++ a/mm/debug_vm_pgtable.c @@ -192,7 +192,7 @@ static void __init pmd_advanced_tests(st

pr_debug("Validating PMD advanced\n"); /* Align the address wrt HPAGE_PMD_SIZE */ - vaddr = (vaddr & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE; + vaddr &= HPAGE_PMD_MASK;

pgtable_trans_huge_deposit(mm, pmdp, pgtable);

@@ -330,7 +330,7 @@ static void __init pud_advanced_tests(st

pr_debug("Validating PUD advanced\n"); /* Align the address wrt HPAGE_PUD_SIZE */ - vaddr = (vaddr & HPAGE_PUD_MASK) + HPAGE_PUD_SIZE; + vaddr &= HPAGE_PUD_MASK;

set_pud_at(mm, vaddr, pudp, pud); pudp_set_wrprotect(mm, vaddr, pudp); _