[PATCH v5 08/10] arm64/mmu: add contiguous bit to sanity bug check

[Ard Biesheuvel]

A mapping with the contiguous bit cannot be safely manipulated while
live, regardless of whether the bit changes between the old and new
mapping. So take this into account when deciding whether the change
is safe.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/mm/mmu.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index d3fecd20a136..a6d7a86dd2b8 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -103,7 +103,15 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
 	 */
 	static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE;
 
-	return old  == 0 || new  == 0 || ((old ^ new) & ~mask) == 0;
+	/* creating or taking down mappings is always safe */
+	if (old == 0 || new == 0)
+		return true;
+
+	/* live contiguous mappings may not be manipulated at all */
+	if ((old | new) & PTE_CONT)
+		return false;
+
+	return ((old ^ new) & ~mask) == 0;
 }
 
 static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
-- 
2.7.4