arm64: compat: Reduce address limit

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@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Jann Horn <jannh@google.com>
Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
[will: fixed typo in comment]
Signed-off-by: Will Deacon <will.deacon@arm.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 902eb708804a55a91dbb51c451fac39a37aec9fe..6401f275e62f3145ba240bdaf634b217111b48b8 100644 (file)
--- 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) ? \