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Diffstat (limited to 'arch/x86/mm/mmap.c')
| -rw-r--r-- | arch/x86/mm/mmap.c | 123 |
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; + } +} |