Messages in this thread Patch in this message | | | From | Pasha Tatashin <> | Subject | [PATCH 1/3] mm/page_table_check: Check writable zero page in page table check | Date | Sun, 11 Sep 2022 09:59:21 +0000 |
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From: Rick Edgecombe <rick.p.edgecombe@intel.com>
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@intel.com> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com> --- 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 e2062748791a..665ece0d55d4 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -102,6 +102,8 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr, if (!pfn_valid(pfn)) return; + BUG_ON(is_zero_pfn(pfn) && rw); + page = pfn_to_page(pfn); page_ext = lookup_page_ext(page); anon = PageAnon(page); -- 2.37.2.789.g6183377224-goog
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