x86: unify mmap_{32|64}.c

mmap_is_ia32 always true for X86_32, or while emulating IA32 on X86_64

Randomization not supported on X86_32 in legacy layout.  Both layouts allow
randomization on X86_64.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 123 insertions, 0 deletions

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
new file mode 100644
index 000000000000..56fe7124fbec
--- /dev/null
+++ b/arch/x86/mm/mmap.c
@@ -0,0 +1,123 @@
+/*
+ * Flexible mmap layout support
+ *
+ * Based on code by Ingo Molnar and Andi Kleen, copyrighted
+ * as follows:
+ *
+ * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
+ * All Rights Reserved.
+ * Copyright 2005 Andi Kleen, SUSE Labs.
+ * Copyright 2007 Jiri Kosina, SUSE Labs.
+ *
+ * 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
+ */
+
+#include <linux/personality.h>
+#include <linux/mm.h>
+#include <linux/random.h>
+#include <linux/limits.h>
+#include <linux/sched.h>
+
+/*
+ * Top of mmap area (just below the process stack).
+ *
+ * Leave an at least ~128 MB hole.
+ */
+#define MIN_GAP (128*1024*1024)
+#define MAX_GAP (TASK_SIZE/6*5)
+
+/*
+ * True on X86_32 or when emulating IA32 on X86_64
+ */
+static int mmap_is_ia32(void)
+{
+#ifdef CONFIG_X86_32
+        return 1;
+#endif
+#ifdef CONFIG_IA32_EMULATION
+        if (test_thread_flag(TIF_IA32))
+                return 1;
+#endif
+        return 0;
+}
+
+static 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;
+}
+
+static unsigned long mmap_rnd(void)
+{
+        unsigned long rnd = 0;
+
+        /*
+        *  8 bits of randomness in 32bit mmaps, 20 address space bits
+        * 28 bits of randomness in 64bit mmaps, 40 address space bits
+        */
+        if (current->flags & PF_RANDOMIZE) {
+                if (mmap_is_ia32())
+                        rnd = (long)get_random_int() % (1<<8);
+                else
+                        rnd = (long)(get_random_int() % (1<<28));
+        }
+        return rnd << PAGE_SHIFT;
+}
+
+static 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());
+}
+
+/*
+ * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
+ * does, but not when emulating X86_32
+ */
+static unsigned long mmap_legacy_base(void)
+{
+        if (mmap_is_ia32())
+                return TASK_UNMAPPED_BASE;
+        else
+                return TASK_UNMAPPED_BASE + 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)
+{
+        if (mmap_is_legacy()) {
+                mm->mmap_base = mmap_legacy_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;
+        }
+}