The current sys_mmap error analysis code doesn't work on 32-bit architectures
with 3G/1G userspace/kernel virtual address space split since the syscall
allocates anonymous memory above the first 2G of the address space ---
such an address is a negative integer so it's interpreted as a error code.
The problem isn't encountered on x86-64 becauase it doesn't use negative
virtual addresses in the userspace.

The 3G/1G split is used because memory allocation is currently broken for other
values of the split on ARM: the value of TASK_UNMAPPED_BASE (arch/arm/include/asm/memory.h)
isn't page-aligned if other split value is used so the value of the field
mm_struct::mmap_base is initialized with a page-unaligned value by
the function arch_pick_mmap_layout() (arch/arm/mm/mmap.c) in some circumstances
that breaks page-alignment checks in the kernel memory management code.

This patch modifies sys_mmap return value analysis code replacing tests
for negativeness of the signed return value with tests that checks that
the return value isn't greater than TASK_SIZE.
Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>