1 files changed, 109 insertions, 0 deletions
diff --git a/arch/powerpc/mm/mmap_64.c b/arch/powerpc/mm/mmap_64.c
new file mode 100644
index 00000000000..0d957a4c70f
--- /dev/null
+++ b/arch/powerpc/mm/mmap_64.c
@@ -0,0 +1,109 @@
+/*
+ *  flexible mmap layout support
+ *
+ * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
+ * All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ *
+ * Started by Ingo Molnar <mingo@elte.hu>
+ */
+
+#include <linux/personality.h>
+#include <linux/mm.h>
+#include <linux/random.h>
+#include <linux/sched.h>
+
+/*
+ * Top of mmap area (just below the process stack).
+ *
+ * Leave at least a ~128 MB hole on 32bit applications.
+ *
+ * On 64bit applications we randomise the stack by 1GB so we need to
+ * space our mmap start address by a further 1GB, otherwise there is a
+ * chance the mmap area will end up closer to the stack than our ulimit
+ * requires.
+ */
+#define MIN_GAP32 (128*1024*1024)
+#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
+#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
+#define MAX_GAP (TASK_SIZE/6*5)
+
+static inline int mmap_is_legacy(void)
+{
+	if (current->personality & ADDR_COMPAT_LAYOUT)
+		return 1;
+
+	if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
+		return 1;
+
+	return sysctl_legacy_va_layout;
+}
+
+/*
+ * Since get_random_int() returns the same value within a 1 jiffy window,
+ * we will almost always get the same randomisation for the stack and mmap
+ * region. This will mean the relative distance between stack and mmap will
+ * be the same.
+ *
+ * To avoid this we can shift the randomness by 1 bit.
+ */
+static unsigned long mmap_rnd(void)
+{
+	unsigned long rnd = 0;
+
+	if (current->flags & PF_RANDOMIZE) {
+		/* 8MB for 32bit, 1GB for 64bit */
+		if (is_32bit_task())
+			rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
+		else
+			rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
+	}
+	return (rnd << PAGE_SHIFT) * 2;
+}
+
+static inline unsigned long mmap_base(void)
+{
+	unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
+
+	if (gap < MIN_GAP)
+		gap = MIN_GAP;
+	else if (gap > MAX_GAP)
+		gap = MAX_GAP;
+
+	return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
+}
+
+/*
+ * This function, called very early during the creation of a new
+ * process VM image, sets up which VM layout function to use:
+ */
+void arch_pick_mmap_layout(struct mm_struct *mm)
+{
+	/*
+	 * Fall back to the standard layout if the personality
+	 * bit is set, or if the expected stack growth is unlimited:
+	 */
+	if (mmap_is_legacy()) {
+		mm->mmap_base = TASK_UNMAPPED_BASE;
+		mm->get_unmapped_area = arch_get_unmapped_area;
+		mm->unmap_area = arch_unmap_area;
+	} else {
+		mm->mmap_base = mmap_base();
+		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
+		mm->unmap_area = arch_unmap_area_topdown;
+	}
+}