[RFC,v2,2/2] Architecture defined limit on memory region random shift.

diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index fa1a392..0ab9f31 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -1301,6 +1301,7 @@  arch_get_unmapped_area_1(unsigned long addr, unsigned long len,
 	info.high_limit = limit;
 	info.align_mask = 0;
 	info.align_offset = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
diff --git a/arch/arc/mm/mmap.c b/arch/arc/mm/mmap.c
index 2e13683..45225fc 100644
--- a/arch/arc/mm/mmap.c
+++ b/arch/arc/mm/mmap.c
@@ -75,5 +75,6 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.high_limit = TASK_SIZE;
 	info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index eb1de66..1eb660c 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -101,6 +101,7 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.high_limit = TASK_SIZE;
 	info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
@@ -152,6 +153,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.high_limit = mm->mmap_base;
 	info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*
diff --git a/arch/frv/mm/elf-fdpic.c b/arch/frv/mm/elf-fdpic.c
index 46aa289..a2ce2ce 100644
--- a/arch/frv/mm/elf-fdpic.c
+++ b/arch/frv/mm/elf-fdpic.c
@@ -86,6 +86,7 @@  unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
 	info.high_limit = (current->mm->start_stack - 0x00200000);
 	info.align_mask = 0;
 	info.align_offset = 0;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 	if (!(addr & ~PAGE_MASK))
 		goto success;
diff --git a/arch/ia64/kernel/sys_ia64.c b/arch/ia64/kernel/sys_ia64.c
index 085adfc..15fa4fb 100644
--- a/arch/ia64/kernel/sys_ia64.c
+++ b/arch/ia64/kernel/sys_ia64.c
@@ -64,6 +64,7 @@  arch_get_unmapped_area (struct file *filp, unsigned long addr, unsigned long len
 	info.high_limit = TASK_SIZE;
 	info.align_mask = align_mask;
 	info.align_offset = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
diff --git a/arch/ia64/mm/hugetlbpage.c b/arch/ia64/mm/hugetlbpage.c
index d16e419..ec7822d 100644
--- a/arch/ia64/mm/hugetlbpage.c
+++ b/arch/ia64/mm/hugetlbpage.c
@@ -162,6 +162,7 @@  unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr, u
 	info.high_limit = HPAGE_REGION_BASE + RGN_MAP_LIMIT;
 	info.align_mask = PAGE_MASK & (HPAGE_SIZE - 1);
 	info.align_offset = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
diff --git a/arch/metag/mm/hugetlbpage.c b/arch/metag/mm/hugetlbpage.c
index 012ee4c..babd325 100644
--- a/arch/metag/mm/hugetlbpage.c
+++ b/arch/metag/mm/hugetlbpage.c
@@ -191,6 +191,7 @@  hugetlb_get_unmapped_area_new_pmd(unsigned long len)
 	info.high_limit = TASK_SIZE;
 	info.align_mask = PAGE_MASK & HUGEPT_MASK;
 	info.align_offset = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
index 33d3251..5a3d384 100644
--- a/arch/mips/mm/mmap.c
+++ b/arch/mips/mm/mmap.c
@@ -122,6 +122,7 @@  static unsigned long arch_get_unmapped_area_common(struct file *filp,
 	info.flags = 0;
 	info.low_limit = mm->mmap_base;
 	info.high_limit = TASK_SIZE;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
index 378a754..abf4b05 100644
--- a/arch/parisc/kernel/sys_parisc.c
+++ b/arch/parisc/kernel/sys_parisc.c
@@ -130,6 +130,7 @@  unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.high_limit = mmap_upper_limit();
 	info.align_mask = last_mmap ? (PAGE_MASK & (SHM_COLOUR - 1)) : 0;
 	info.align_offset = shared_align_offset(last_mmap, pgoff);
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 found_addr:
@@ -192,6 +193,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.high_limit = mm->mmap_base;
 	info.align_mask = last_mmap ? (PAGE_MASK & (SHM_COLOUR - 1)) : 0;
 	info.align_offset = shared_align_offset(last_mmap, pgoff);
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 	if (!(addr & ~PAGE_MASK))
 		goto found_addr;
diff --git a/arch/powerpc/mm/hugetlbpage-radix.c b/arch/powerpc/mm/hugetlbpage-radix.c
index 2486bee..1d61a88 100644
--- a/arch/powerpc/mm/hugetlbpage-radix.c
+++ b/arch/powerpc/mm/hugetlbpage-radix.c
@@ -87,6 +87,7 @@  radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	info.high_limit = mm->mmap_base + (high_limit - DEFAULT_MAP_WINDOW);
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = 0;
 
 	return vm_unmapped_area(&info);
 }
diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
index d503f34..7fe98c7 100644
--- a/arch/powerpc/mm/mmap.c
+++ b/arch/powerpc/mm/mmap.c
@@ -136,6 +136,7 @@  radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.low_limit = mm->mmap_base;
 	info.high_limit = high_limit;
 	info.align_mask = 0;
+	info.random_shift = 0;
 
 	return vm_unmapped_area(&info);
 }
@@ -180,6 +181,7 @@  radix__arch_get_unmapped_area_topdown(struct file *filp,
 	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 	info.high_limit = mm->mmap_base + (high_limit - DEFAULT_MAP_WINDOW);
 	info.align_mask = 0;
+	info.random_shift = 0;
 
 	addr = vm_unmapped_area(&info);
 	if (!(addr & ~PAGE_MASK))
diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index 23ec2c5..2005845 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c
@@ -284,6 +284,7 @@  static unsigned long slice_find_area_bottomup(struct mm_struct *mm,
 	info.length = len;
 	info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
 	info.align_offset = 0;
+	info.random_shift = 0;
 
 	addr = TASK_UNMAPPED_BASE;
 	/*
@@ -330,6 +331,7 @@  static unsigned long slice_find_area_topdown(struct mm_struct *mm,
 	info.length = len;
 	info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
 	info.align_offset = 0;
+	info.random_shift = 0;
 
 	addr = mm->mmap_base;
 	/*
diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 831bdcf..141823f 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -95,6 +95,7 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.length = len;
 	info.low_limit = mm->mmap_base;
 	info.high_limit = TASK_SIZE;
+	info.random_shift = 0;
 	if (filp || (flags & MAP_SHARED))
 		info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
 	else
@@ -146,6 +147,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.length = len;
 	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 	info.high_limit = mm->mmap_base;
+	info.random_shift = 0;
 	if (filp || (flags & MAP_SHARED))
 		info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
 	else
diff --git a/arch/sh/mm/mmap.c b/arch/sh/mm/mmap.c
index 6a1a129..d9206c2 100644
--- a/arch/sh/mm/mmap.c
+++ b/arch/sh/mm/mmap.c
@@ -74,6 +74,7 @@  unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.high_limit = TASK_SIZE;
 	info.align_mask = do_colour_align ? (PAGE_MASK & shm_align_mask) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
@@ -124,6 +125,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.high_limit = mm->mmap_base;
 	info.align_mask = do_colour_align ? (PAGE_MASK & shm_align_mask) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*
diff --git a/arch/sparc/kernel/sys_sparc_32.c b/arch/sparc/kernel/sys_sparc_32.c
index 990703b7..af664ba3 100644
--- a/arch/sparc/kernel/sys_sparc_32.c
+++ b/arch/sparc/kernel/sys_sparc_32.c
@@ -66,6 +66,7 @@  unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
 	info.align_mask = (flags & MAP_SHARED) ?
 		(PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
index 55416db..3d12e3d 100644
--- a/arch/sparc/kernel/sys_sparc_64.c
+++ b/arch/sparc/kernel/sys_sparc_64.c
@@ -131,6 +131,7 @@  unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, unsi
 	info.high_limit = min(task_size, VA_EXCLUDE_START);
 	info.align_mask = do_color_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	if ((addr & ~PAGE_MASK) && task_size > VA_EXCLUDE_END) {
@@ -194,6 +195,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.high_limit = mm->mmap_base;
 	info.align_mask = do_color_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*
diff --git a/arch/sparc/mm/hugetlbpage.c b/arch/sparc/mm/hugetlbpage.c
index 0112d69..6d0c032 100644
--- a/arch/sparc/mm/hugetlbpage.c
+++ b/arch/sparc/mm/hugetlbpage.c
@@ -43,6 +43,7 @@  static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *filp,
 	info.high_limit = min(task_size, VA_EXCLUDE_START);
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	if ((addr & ~PAGE_MASK) && task_size > VA_EXCLUDE_END) {
@@ -75,6 +76,7 @@  hugetlb_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.high_limit = mm->mmap_base;
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*
diff --git a/arch/tile/mm/hugetlbpage.c b/arch/tile/mm/hugetlbpage.c
index 0986d42..2b3a9b6 100644
--- a/arch/tile/mm/hugetlbpage.c
+++ b/arch/tile/mm/hugetlbpage.c
@@ -176,6 +176,7 @@  static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
 	info.high_limit = TASK_SIZE;
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 
@@ -193,6 +194,7 @@  static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
 	info.high_limit = current->mm->mmap_base;
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = 0;
 	addr = vm_unmapped_area(&info);
 
 	/*
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 676774b..0eda047 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -163,6 +163,8 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.high_limit = end;
 	info.align_mask = 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = in_compat_syscall() ?
+		256 : 0x1000000;
 	if (filp) {
 		info.align_mask = get_align_mask();
 		info.align_offset += get_align_bits();
@@ -224,6 +226,8 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 
 	info.align_mask = 0;
 	info.align_offset = pgoff << PAGE_SHIFT;
+	info.random_shift = in_compat_syscall() ?
+		256 : 0x1000000;
 	if (filp) {
 		info.align_mask = get_align_mask();
 		info.align_offset += get_align_bits();
diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 00b2966..f4f6436 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -97,6 +97,8 @@  static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
 
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = in_compat_syscall() ?
+		256 : 0x1000000;
 	return vm_unmapped_area(&info);
 }
 
@@ -121,6 +123,8 @@  static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
 
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = in_compat_syscall() ?
+		256 : 0x1000000;
 	addr = vm_unmapped_area(&info);
 
 	/*
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 8fe1b0a..83e962e 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -200,6 +200,7 @@  hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	info.high_limit = TASK_SIZE;
 	info.align_mask = PAGE_MASK & ~huge_page_mask(h);
 	info.align_offset = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 #endif
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c716257..f869e6d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2252,6 +2252,7 @@  struct vm_unmapped_area_info {
 	unsigned long high_limit;
 	unsigned long align_mask;
 	unsigned long align_offset;
+	unsigned long random_shift;
 };
 
 #ifndef CONFIG_MMU
diff --git a/mm/mmap.c b/mm/mmap.c
index ba9cebb..425fa09 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1938,7 +1938,7 @@  unsigned long unmapped_area_random(struct vm_unmapped_area_info *info)
 	if (gap_end ==  gap_start)
 		return gap_start;
 	addr = entropy[1] % (min((gap_end - gap_start) >> PAGE_SHIFT,
-							 0x10000UL));
+							 info->random_shift));
 	addr = gap_end - (addr << PAGE_SHIFT);
 	addr += (info->align_offset - addr) & info->align_mask;
 	return addr;
@@ -2186,6 +2186,7 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.low_limit = mm->mmap_base;
 	info.high_limit = TASK_SIZE;
 	info.align_mask = 0;
+	info.random_shift = 0;
 	return vm_unmapped_area(&info);
 }
 #endif