x86: PIE executable randomization

main executable of (specially compiled/linked -pie/-fpie) ET_DYN binaries
onto a random address (in cases in which mmap() is allowed to perform a
randomization).

The code has been extraced from Ingo's exec-shield patch
http://people.redhat.com/mingo/exec-shield/

[akpm@linux-foundation.org: fix used-uninitialsied warning]
[kamezawa.hiroyu@jp.fujitsu.com: fixed ia32 ELF on x86_64 handling]

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 200 insertions, 17 deletions

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 907942ee6e76..95485e63fd2f 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -12,6 +12,7 @@
 #include <linux/file.h>
 #include <linux/utsname.h>
 #include <linux/personality.h>
+#include <linux/random.h>
 
 #include <asm/uaccess.h>
 #include <asm/ia32.h>
@@ -65,6 +66,7 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
                            unsigned long *end)
 {
         if (!test_thread_flag(TIF_IA32) && (flags & MAP_32BIT)) {
+                unsigned long new_begin;
                 /* This is usually used needed to map code in small
                    model, so it needs to be in the first 31bit. Limit
                    it to that.  This means we need to move the
@@ -74,6 +76,11 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
                    of playground for now. -AK */ 
                 *begin = 0x40000000; 
                 *end = 0x80000000;              
+                if (current->flags & PF_RANDOMIZE) {
+                        new_begin = randomize_range(*begin, *begin + 0x02000000, 0);
+                        if (new_begin)
+                                *begin = new_begin;
+                }
         } else {
                 *begin = TASK_UNMAPPED_BASE;
                 *end = TASK_SIZE; 
@@ -143,6 +150,97 @@ full_search:
         }
 }
 
+
+unsigned long
+arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
+                          const unsigned long len, const unsigned long pgoff,
+                          const unsigned long flags)
+{
+        struct vm_area_struct *vma;
+        struct mm_struct *mm = current->mm;
+        unsigned long addr = addr0;
+
+        /* requested length too big for entire address space */
+        if (len > TASK_SIZE)
+                return -ENOMEM;
+
+        if (flags & MAP_FIXED)
+                return addr;
+
+        /* for MAP_32BIT mappings we force the legact mmap base */
+        if (!test_thread_flag(TIF_IA32) && (flags & MAP_32BIT))
+                goto bottomup;
+
+        /* requesting a specific address */
+        if (addr) {
+                addr = PAGE_ALIGN(addr);
+                vma = find_vma(mm, addr);
+                if (TASK_SIZE - len >= addr &&
+                                (!vma || addr + len <= vma->vm_start))
+                        return addr;
+        }
+
+        /* check if free_area_cache is useful for us */
+        if (len <= mm->cached_hole_size) {
+                mm->cached_hole_size = 0;
+                mm->free_area_cache = mm->mmap_base;
+        }
+
+        /* either no address requested or can't fit in requested address hole */
+        addr = mm->free_area_cache;
+
+        /* make sure it can fit in the remaining address space */
+        if (addr > len) {
+                vma = find_vma(mm, addr-len);
+                if (!vma || addr <= vma->vm_start)
+                        /* remember the address as a hint for next time */
+                        return (mm->free_area_cache = addr-len);
+        }
+
+        if (mm->mmap_base < len)
+                goto bottomup;
+
+        addr = mm->mmap_base-len;
+
+        do {
+                /*
+                 * Lookup failure means no vma is above this address,
+                 * else if new region fits below vma->vm_start,
+                 * return with success:
+                 */
+                vma = find_vma(mm, addr);
+                if (!vma || addr+len <= vma->vm_start)
+                        /* remember the address as a hint for next time */
+                        return (mm->free_area_cache = addr);
+
+                /* remember the largest hole we saw so far */
+                if (addr + mm->cached_hole_size < vma->vm_start)
+                        mm->cached_hole_size = vma->vm_start - addr;
+
+                /* try just below the current vma->vm_start */
+                addr = vma->vm_start-len;
+        } while (len < vma->vm_start);
+
+bottomup:
+        /*
+         * A failed mmap() very likely causes application failure,
+         * so fall back to the bottom-up function here. This scenario
+         * can happen with large stack limits and large mmap()
+         * allocations.
+         */
+        mm->cached_hole_size = ~0UL;
+        mm->free_area_cache = TASK_UNMAPPED_BASE;
+        addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
+        /*
+         * Restore the topdown base:
+         */
+        mm->free_area_cache = mm->mmap_base;
+        mm->cached_hole_size = ~0UL;
+
+        return addr;
+}
+
+
 asmlinkage long sys_uname(struct new_utsname __user * name)
 {
         int err;
diff --git a/arch/x86/mm/mmap_64.c b/arch/x86/mm/mmap_64.c
index ffb71a31bb6e..8cf03ea651f8 100644
--- a/arch/x86/mm/mmap_64.c
+++ b/arch/x86/mm/mmap_64.c
@@ -1,32 +1,117 @@
-/* Copyright 2005 Andi Kleen, SuSE Labs.
- * Licensed under GPL, v.2
+/*
+ *  linux/arch/x86-64/mm/mmap.c
+ *
+ *  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/sched.h>
 #include <linux/random.h>
+#include <linux/limits.h>
+#include <linux/sched.h>
 #include <asm/ia32.h>
 
-/* Notebook: move the mmap code from sys_x86_64.c over here. */
+/*
+ * 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)
 
-void arch_pick_mmap_layout(struct mm_struct *mm)
+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 TASK_SIZE - (gap & PAGE_MASK);
+}
+
+static inline int mmap_is_32(void)
 {
 #ifdef CONFIG_IA32_EMULATION
-        if (current_thread_info()->flags & _TIF_IA32)
-                return ia32_pick_mmap_layout(mm);
+        if (test_thread_flag(TIF_IA32))
+                return 1;
 #endif
-        mm->mmap_base = TASK_UNMAPPED_BASE;
+        return 0;
+}
+
+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;
+}
+
+/*
+ * 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)
+{
+        int rnd = 0;
         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)
+                 * 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;
+                rnd = get_random_int() & 0xfffffff;
+        }
 
-                mm->mmap_base += ((unsigned long)rnd) << PAGE_SHIFT;
+        /*
+         * Fall back to the standard layout if the personality
+         * bit is set, or if the expected stack growth is unlimited:
+         */
+        if (mmap_is_32()) {
+#ifdef CONFIG_IA32_EMULATION
+                /* ia32_pick_mmap_layout has its own. */
+                return ia32_pick_mmap_layout(mm);
+#endif
+        } else 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;
+                if (current->flags & PF_RANDOMIZE)
+                        rnd = -rnd;
+        }
+        if (current->flags & PF_RANDOMIZE) {
+                mm->mmap_base += ((long)rnd) << PAGE_SHIFT;
         }
-        mm->get_unmapped_area = arch_get_unmapped_area;
-        mm->unmap_area = arch_unmap_area;
 }
-