From: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> The zero page should remain all zero, so that it can be mapped as read-only for read faults of memory that should be zeroed. If it is ever mapped writable to userspace, it could become non-zero and so other apps would unexpectedly get non-zero data. So the zero page should never be mapped writable to userspace. Check for this condition in page_table_check_set(). Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> --- mm/page_table_check.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/page_table_check.c b/mm/page_table_check.c index ad4447e999f8..db1ed36f7203 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -114,6 +114,8 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr, if (!pfn_valid(pfn)) return; + PAGE_TABLE_CHECK_WARN(is_zero_pfn(pfn) && rw); + page = pfn_to_page(pfn); page_ext = page_ext_get(page); -- 2.41.0.487.g6d72f3e995-goog
