1/* 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 5 */ 6#include <linux/mm.h> 7#include <linux/err.h> 8#include <linux/sched.h> 9#include <linux/slab.h> 10#include <linux/init.h> 11#include <linux/random.h> 12#include <linux/elf.h> 13#include <asm/vsyscall.h> 14#include <asm/vgtod.h> 15#include <asm/proto.h> 16#include <asm/vdso.h> 17 18#include "vextern.h" /* Just for VMAGIC. */ 19#undef VEXTERN 20 21unsigned int __read_mostly vdso_enabled = 1; 22 23extern char vdso_start[], vdso_end[]; 24extern unsigned short vdso_sync_cpuid; 25 26static struct page **vdso_pages; 27static unsigned vdso_size; 28 29static inline void *var_ref(void *p, char *name) 30{ 31 if (*(void **)p != (void *)VMAGIC) { 32 printk("VDSO: variable %s broken\n", name); 33 vdso_enabled = 0; 34 } 35 return p; 36} 37 38static int __init init_vdso_vars(void) 39{ 40 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE; 41 int i; 42 char *vbase; 43 44 vdso_size = npages << PAGE_SHIFT; 45 vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL); 46 if (!vdso_pages) 47 goto oom; 48 for (i = 0; i < npages; i++) { 49 struct page *p; 50 p = alloc_page(GFP_KERNEL); 51 if (!p) 52 goto oom; 53 vdso_pages[i] = p; 54 copy_page(page_address(p), vdso_start + i*PAGE_SIZE); 55 } 56 57 vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL); 58 if (!vbase) 59 goto oom; 60 61 if (memcmp(vbase, "\177ELF", 4)) { 62 printk("VDSO: I'm broken; not ELF\n"); 63 vdso_enabled = 0; 64 } 65 66#define VEXTERN(x) \ 67 *(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x; 68#include "vextern.h" 69#undef VEXTERN 70 vunmap(vbase); 71 return 0; 72 73 oom: 74 printk("Cannot allocate vdso\n"); 75 vdso_enabled = 0; 76 return -ENOMEM; 77} 78subsys_initcall(init_vdso_vars); 79 80struct linux_binprm; 81 82/* Put the vdso above the (randomized) stack with another randomized offset. 83 This way there is no hole in the middle of address space. 84 To save memory make sure it is still in the same PTE as the stack top. 85 This doesn't give that many random bits */ 86static unsigned long vdso_addr(unsigned long start, unsigned len) 87{ 88 unsigned long addr, end; 89 unsigned offset; 90 end = (start + PMD_SIZE - 1) & PMD_MASK; 91 if (end >= TASK_SIZE_MAX) 92 end = TASK_SIZE_MAX; 93 end -= len; 94 /* This loses some more bits than a modulo, but is cheaper */ 95 offset = get_random_int() & (PTRS_PER_PTE - 1); 96 addr = start + (offset << PAGE_SHIFT); 97 if (addr >= end) 98 addr = end; 99 return addr; 100} 101 102/* Setup a VMA at program startup for the vsyscall page. 103 Not called for compat tasks */ 104int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp) 105{ 106 struct mm_struct *mm = current->mm; 107 unsigned long addr; 108 int ret; 109 110 if (!vdso_enabled) 111 return 0; 112 113 down_write(&mm->mmap_sem); 114 addr = vdso_addr(mm->start_stack, vdso_size); 115 addr = get_unmapped_area(NULL, addr, vdso_size, 0, 0); 116 if (IS_ERR_VALUE(addr)) { 117 ret = addr; 118 goto up_fail; 119 } 120 121 current->mm->context.vdso = (void *)addr; 122 123 ret = install_special_mapping(mm, addr, vdso_size, 124 VM_READ|VM_EXEC| 125 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC| 126 VM_ALWAYSDUMP, 127 vdso_pages); 128 if (ret) { 129 current->mm->context.vdso = NULL; 130 goto up_fail; 131 } 132 133up_fail: 134 up_write(&mm->mmap_sem); 135 return ret; 136} 137 138static __init int vdso_setup(char *s) 139{ 140 vdso_enabled = simple_strtoul(s, NULL, 0); 141 return 0; 142} 143__setup("vdso=", vdso_setup); 144