m68knommu: set ZERO_PAGE() to the allocated zeroed page

[ Upstream commit dc068f46217970d9516f16cd37972a01d50dc055 ]

The non-MMU m68k pagetable ZERO_PAGE() macro is being set to the
somewhat non-sensical value of "virt_to_page(0)". The zeroth page
is not in any way guaranteed to be a page full of "0". So the result
is that ZERO_PAGE() will almost certainly contain random values.

We already allocate a real "empty_zero_page" in the mm setup code shared
between MMU m68k and non-MMU m68k. It is just not hooked up to the
ZERO_PAGE() macro for the non-MMU m68k case.

Fix ZERO_PAGE() to use the allocated "empty_zero_page" pointer.

I am not aware of any specific issues caused by the old code.

Link: https://lore.kernel.org/linux-m68k/2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@google.com/T/#t
Reported-by: Hugh Dickens <hughd@google.com>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/m68k/include/asm/pgtable_no.h b/arch/m68k/include/asm/pgtable_no.h
index ac7d87a02335e2280281ec99e5e60fe30532e81d..269443e1084b3935552a3f07806b966c345be52d 100644 (file)
--- a/arch/m68k/include/asm/pgtable_no.h
+++ b/arch/m68k/include/asm/pgtable_no.h
@@ -41,7 +41,8 @@ extern void paging_init(void);
  * ZERO_PAGE is a global shared page that is always zero: used
  * for zero-mapped memory areas etc..
  */
-#define ZERO_PAGE(vaddr)       (virt_to_page(0))
+extern void *empty_zero_page;
+#define ZERO_PAGE(vaddr)       (virt_to_page(empty_zero_page))
 
 /*
  * No page table caches to initialise.