[PATCH] x86_64: Flexmap for 32bit and randomized mappings for 64bit

Another try at this.

For 32bit follow the 32bit implementation from Ingo -
mappings are growing down from the end of stack now
and vary randomly by 1GB.

Randomized mappings for 64bit just vary the normal mmap break
by 1TB. I didn't bother implementing full flex mmap for 64bit
because it shouldn't be needed there.

Cc: mingo@elte.hu

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/arch/x86_64/mm/mmap.c b/arch/x86_64/mm/mmap.c
new file mode 100644
index 000000000000..43e9b99bdf25
--- /dev/null
+++ b/arch/x86_64/mm/mmap.c
@@ -0,0 +1,30 @@
+/* Copyright 2005 Andi Kleen, SuSE Labs.
+ * Licensed under GPL, v.2
+ */
+#include <linux/config.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/random.h>
+#include <asm/ia32.h>
+
+/* Notebook: move the mmap code from sys_x86_64.c over here. */
+
+void arch_pick_mmap_layout(struct mm_struct *mm)
+{
+#ifdef CONFIG_IA32_EMULATION
+        if (current_thread_info()->flags & _TIF_IA32)
+                return ia32_pick_mmap_layout(mm);
+#endif
+        mm->mmap_base = TASK_UNMAPPED_BASE;
+        if (current->flags & PF_RANDOMIZE) {
+                /* Add 28bit randomness which is about 40bits of address space
+                   because mmap base has to be page aligned.
+                   or ~1/128 of the total user VM
+                   (total user address space is 47bits) */
+                unsigned rnd = get_random_int() & 0xfffffff;
+                mm->mmap_base += ((unsigned long)rnd) << PAGE_SHIFT;
+        }
+        mm->get_unmapped_area = arch_get_unmapped_area;
+        mm->unmap_area = arch_unmap_area;
+}
+