[PATCH 3.16 026/132] arm64: compat: Reduce address limit

[Ben Hutchings]

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>

commit d263119387de9975d2acba1dfd3392f7c5979c18 upstream.

Currently, compat tasks running on arm64 can allocate memory up to
TASK_SIZE_32 (UL(0x100000000)).

This means that mmap() allocations, if we treat them as returning an
array, are not compliant with the sections 6.5.8 of the C standard
(C99) which states that: "If the expression P points to an element of
an array object and the expression Q points to the last element of the
same array object, the pointer expression Q+1 compares greater than P".

Redefine TASK_SIZE_32 to address the issue.

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
[will: fixed typo in comment]
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/arm64/include/asm/memory.h | 8 ++++++++
 1 file changed, 8 insertions(+)

--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -53,7 +53,15 @@
 #define TASK_SIZE_64		(UL(1) << VA_BITS)
 
 #ifdef CONFIG_COMPAT
+#ifdef CONFIG_ARM64_64K_PAGES
+/*
+ * With CONFIG_ARM64_64K_PAGES enabled, the last page is occupied
+ * by the compat vectors page.
+ */
 #define TASK_SIZE_32		UL(0x100000000)
+#else
+#define TASK_SIZE_32		(UL(0x100000000) - PAGE_SIZE)
+#endif /* CONFIG_ARM64_64K_PAGES */
 #define TASK_SIZE		(test_thread_flag(TIF_32BIT) ? \
 				TASK_SIZE_32 : TASK_SIZE_64)
 #define TASK_SIZE_OF(tsk)	(test_tsk_thread_flag(tsk, TIF_32BIT) ? \