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Subject[PATCH v2 3/3] mm/page_table_check: Check writable zero page in page table check
Date
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 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
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