2 * Set up the VMAs to tell the VM about the vDSO.
3 * Copyright 2007 Andi Kleen, SUSE Labs.
4 * Subject to the GPL, v.2
8 #include <linux/sched.h>
9 #include <linux/init.h>
10 #include <linux/random.h>
11 #include <asm/vsyscall.h>
12 #include <asm/vgtod.h>
13 #include <asm/proto.h>
16 #include "vextern.h" /* Just for VMAGIC. */
19 unsigned int __read_mostly vdso_enabled
= 1;
21 extern char vdso_start
[], vdso_end
[];
22 extern unsigned short vdso_sync_cpuid
;
24 static struct page
**vdso_pages
;
25 static unsigned vdso_size
;
27 static inline void *var_ref(void *p
, char *name
)
29 if (*(void **)p
!= (void *)VMAGIC
) {
30 printk("VDSO: variable %s broken\n", name
);
36 static int __init
init_vdso_vars(void)
38 int npages
= (vdso_end
- vdso_start
+ PAGE_SIZE
- 1) / PAGE_SIZE
;
42 vdso_size
= npages
<< PAGE_SHIFT
;
43 vdso_pages
= kmalloc(sizeof(struct page
*) * npages
, GFP_KERNEL
);
46 for (i
= 0; i
< npages
; i
++) {
48 p
= alloc_page(GFP_KERNEL
);
52 copy_page(page_address(p
), vdso_start
+ i
*PAGE_SIZE
);
55 vbase
= vmap(vdso_pages
, npages
, 0, PAGE_KERNEL
);
59 if (memcmp(vbase
, "\177ELF", 4)) {
60 printk("VDSO: I'm broken; not ELF\n");
65 *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
71 printk("Cannot allocate vdso\n");
75 __initcall(init_vdso_vars
);
79 /* Put the vdso above the (randomized) stack with another randomized offset.
80 This way there is no hole in the middle of address space.
81 To save memory make sure it is still in the same PTE as the stack top.
82 This doesn't give that many random bits */
83 static unsigned long vdso_addr(unsigned long start
, unsigned len
)
85 unsigned long addr
, end
;
87 end
= (start
+ PMD_SIZE
- 1) & PMD_MASK
;
88 if (end
>= TASK_SIZE_MAX
)
91 /* This loses some more bits than a modulo, but is cheaper */
92 offset
= get_random_int() & (PTRS_PER_PTE
- 1);
93 addr
= start
+ (offset
<< PAGE_SHIFT
);
99 /* Setup a VMA at program startup for the vsyscall page.
100 Not called for compat tasks */
101 int arch_setup_additional_pages(struct linux_binprm
*bprm
, int uses_interp
)
103 struct mm_struct
*mm
= current
->mm
;
110 down_write(&mm
->mmap_sem
);
111 addr
= vdso_addr(mm
->start_stack
, vdso_size
);
112 addr
= get_unmapped_area(NULL
, addr
, vdso_size
, 0, 0);
113 if (IS_ERR_VALUE(addr
)) {
118 current
->mm
->context
.vdso
= (void *)addr
;
120 ret
= install_special_mapping(mm
, addr
, vdso_size
,
122 VM_MAYREAD
|VM_MAYWRITE
|VM_MAYEXEC
|
126 current
->mm
->context
.vdso
= NULL
;
131 up_write(&mm
->mmap_sem
);
135 static __init
int vdso_setup(char *s
)
137 vdso_enabled
= simple_strtoul(s
, NULL
, 0);
140 __setup("vdso=", vdso_setup
);