arch/sh/kernel/vsyscall/vsyscall.c

   1 /*
   2  * arch/sh/kernel/vsyscall/vsyscall.c
   3  *
   4  *  Copyright (C) 2006 Paul Mundt
   5  *
   6  * vDSO randomization
   7  * Copyright(C) 2005-2006, Red Hat, Inc., Ingo Molnar
   8  *
   9  * This file is subject to the terms and conditions of the GNU General Public
  10  * License.  See the file "COPYING" in the main directory of this archive
  11  * for more details.
  12  */
  13 #include <linux/mm.h>
  14 #include <linux/kernel.h>
  15 #include <linux/init.h>
  16 #include <linux/gfp.h>
  17 #include <linux/module.h>
  18 #include <linux/elf.h>
  19 #include <linux/sched.h>
  20 #include <linux/err.h>
  21
  22 /*
  23  * Should the kernel map a VDSO page into processes and pass its
  24  * address down to glibc upon exec()?
  25  */
  26 unsigned int __read_mostly vdso_enabled = 1;
  27 EXPORT_SYMBOL_GPL(vdso_enabled);
  28
  29 static int __init vdso_setup(char *s)
  30 {
  31         vdso_enabled = simple_strtoul(s, NULL, 0);
  32         return 1;
  33 }
  34 __setup("vdso=", vdso_setup);
  35
  36 /*
  37  * These symbols are defined by vsyscall.o to mark the bounds
  38  * of the ELF DSO images included therein.
  39  */
  40 extern const char vsyscall_trapa_start, vsyscall_trapa_end;
  41 static struct page *syscall_pages[1];
  42
  43 int __init vsyscall_init(void)
  44 {
  45         void *syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
  46         syscall_pages[0] = virt_to_page(syscall_page);
  47
  48         /*
  49          * XXX: Map this page to a fixmap entry if we get around
  50          * to adding the page to ELF core dumps
  51          */
  52
  53         memcpy(syscall_page,
  54                &vsyscall_trapa_start,
  55                &vsyscall_trapa_end - &vsyscall_trapa_start);
  56
  57         return 0;
  58 }
  59
  60 /* Setup a VMA at program startup for the vsyscall page */
  61 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
  62 {
  63         struct mm_struct *mm = current->mm;
  64         unsigned long addr;
  65         int ret;
  66
  67         down_write(&mm->mmap_sem);
  68         addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
  69         if (IS_ERR_VALUE(addr)) {
  70                 ret = addr;
  71                 goto up_fail;
  72         }
  73
  74         ret = install_special_mapping(mm, addr, PAGE_SIZE,
  75                                       VM_READ | VM_EXEC |
  76                                       VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
  77                                       syscall_pages);
  78         if (unlikely(ret))
  79                 goto up_fail;
  80
  81         current->mm->context.vdso = (void *)addr;
  82
  83 up_fail:
  84         up_write(&mm->mmap_sem);
  85         return ret;
  86 }
  87
  88 const char *arch_vma_name(struct vm_area_struct *vma)
  89 {
  90         if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
  91                 return "[vdso]";
  92
  93         return NULL;
  94 }