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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 #include <asm/page.h>
18 #include <asm/hpet.h>
19 
20 #if defined(CONFIG_X86_64)
21 unsigned int __read_mostly vdso64_enabled = 1;
22 
23 extern unsigned short vdso_sync_cpuid;
24 #endif
25 
init_vdso_image(const struct vdso_image * image)26 void __init init_vdso_image(const struct vdso_image *image)
27 {
28 	int i;
29 	int npages = (image->size) / PAGE_SIZE;
30 
31 	BUG_ON(image->size % PAGE_SIZE != 0);
32 	for (i = 0; i < npages; i++)
33 		image->text_mapping.pages[i] =
34 			virt_to_page(image->data + i*PAGE_SIZE);
35 
36 	apply_alternatives((struct alt_instr *)(image->data + image->alt),
37 			   (struct alt_instr *)(image->data + image->alt +
38 						image->alt_len));
39 }
40 
41 #if defined(CONFIG_X86_64)
init_vdso(void)42 static int __init init_vdso(void)
43 {
44 	init_vdso_image(&vdso_image_64);
45 
46 #ifdef CONFIG_X86_X32_ABI
47 	init_vdso_image(&vdso_image_x32);
48 #endif
49 
50 	return 0;
51 }
52 subsys_initcall(init_vdso);
53 #endif
54 
55 struct linux_binprm;
56 
57 /*
58  * Put the vdso above the (randomized) stack with another randomized
59  * offset.  This way there is no hole in the middle of address space.
60  * To save memory make sure it is still in the same PTE as the stack
61  * top.  This doesn't give that many random bits.
62  *
63  * Note that this algorithm is imperfect: the distribution of the vdso
64  * start address within a PMD is biased toward the end.
65  *
66  * Only used for the 64-bit and x32 vdsos.
67  */
vdso_addr(unsigned long start,unsigned len)68 static unsigned long vdso_addr(unsigned long start, unsigned len)
69 {
70 #ifdef CONFIG_X86_32
71 	return 0;
72 #else
73 	unsigned long addr, end;
74 	unsigned offset;
75 
76 	/*
77 	 * Round up the start address.  It can start out unaligned as a result
78 	 * of stack start randomization.
79 	 */
80 	start = PAGE_ALIGN(start);
81 
82 	/* Round the lowest possible end address up to a PMD boundary. */
83 	end = (start + len + PMD_SIZE - 1) & PMD_MASK;
84 	if (end >= TASK_SIZE_MAX)
85 		end = TASK_SIZE_MAX;
86 	end -= len;
87 
88 	if (end > start) {
89 		offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
90 		addr = start + (offset << PAGE_SHIFT);
91 	} else {
92 		addr = start;
93 	}
94 
95 	/*
96 	 * Forcibly align the final address in case we have a hardware
97 	 * issue that requires alignment for performance reasons.
98 	 */
99 	addr = align_vdso_addr(addr);
100 
101 	return addr;
102 #endif
103 }
104 
map_vdso(const struct vdso_image * image,bool calculate_addr)105 static int map_vdso(const struct vdso_image *image, bool calculate_addr)
106 {
107 	struct mm_struct *mm = current->mm;
108 	struct vm_area_struct *vma;
109 	unsigned long addr, text_start;
110 	int ret = 0;
111 	static struct page *no_pages[] = {NULL};
112 	static struct vm_special_mapping vvar_mapping = {
113 		.name = "[vvar]",
114 		.pages = no_pages,
115 	};
116 
117 	if (calculate_addr) {
118 		addr = vdso_addr(current->mm->start_stack,
119 				 image->size - image->sym_vvar_start);
120 	} else {
121 		addr = 0;
122 	}
123 
124 	down_write(&mm->mmap_sem);
125 
126 	addr = get_unmapped_area(NULL, addr,
127 				 image->size - image->sym_vvar_start, 0, 0);
128 	if (IS_ERR_VALUE(addr)) {
129 		ret = addr;
130 		goto up_fail;
131 	}
132 
133 	text_start = addr - image->sym_vvar_start;
134 	current->mm->context.vdso = (void __user *)text_start;
135 
136 	/*
137 	 * MAYWRITE to allow gdb to COW and set breakpoints
138 	 */
139 	vma = _install_special_mapping(mm,
140 				       text_start,
141 				       image->size,
142 				       VM_READ|VM_EXEC|
143 				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
144 				       &image->text_mapping);
145 
146 	if (IS_ERR(vma)) {
147 		ret = PTR_ERR(vma);
148 		goto up_fail;
149 	}
150 
151 	vma = _install_special_mapping(mm,
152 				       addr,
153 				       -image->sym_vvar_start,
154 				       VM_READ|VM_MAYREAD,
155 				       &vvar_mapping);
156 
157 	if (IS_ERR(vma)) {
158 		ret = PTR_ERR(vma);
159 		goto up_fail;
160 	}
161 
162 	if (image->sym_vvar_page)
163 		ret = remap_pfn_range(vma,
164 				      text_start + image->sym_vvar_page,
165 				      __pa_symbol(&__vvar_page) >> PAGE_SHIFT,
166 				      PAGE_SIZE,
167 				      PAGE_READONLY);
168 
169 	if (ret)
170 		goto up_fail;
171 
172 #ifdef CONFIG_HPET_TIMER
173 	if (hpet_address && image->sym_hpet_page) {
174 		ret = io_remap_pfn_range(vma,
175 			text_start + image->sym_hpet_page,
176 			hpet_address >> PAGE_SHIFT,
177 			PAGE_SIZE,
178 			pgprot_noncached(PAGE_READONLY));
179 
180 		if (ret)
181 			goto up_fail;
182 	}
183 #endif
184 
185 up_fail:
186 	if (ret)
187 		current->mm->context.vdso = NULL;
188 
189 	up_write(&mm->mmap_sem);
190 	return ret;
191 }
192 
193 #if defined(CONFIG_X86_32) || defined(CONFIG_COMPAT)
load_vdso32(void)194 static int load_vdso32(void)
195 {
196 	int ret;
197 
198 	if (vdso32_enabled != 1)  /* Other values all mean "disabled" */
199 		return 0;
200 
201 	ret = map_vdso(selected_vdso32, false);
202 	if (ret)
203 		return ret;
204 
205 	if (selected_vdso32->sym_VDSO32_SYSENTER_RETURN)
206 		current_thread_info()->sysenter_return =
207 			current->mm->context.vdso +
208 			selected_vdso32->sym_VDSO32_SYSENTER_RETURN;
209 
210 	return 0;
211 }
212 #endif
213 
214 #ifdef CONFIG_X86_64
arch_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)215 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
216 {
217 	if (!vdso64_enabled)
218 		return 0;
219 
220 	return map_vdso(&vdso_image_64, true);
221 }
222 
223 #ifdef CONFIG_COMPAT
compat_arch_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)224 int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
225 				       int uses_interp)
226 {
227 #ifdef CONFIG_X86_X32_ABI
228 	if (test_thread_flag(TIF_X32)) {
229 		if (!vdso64_enabled)
230 			return 0;
231 
232 		return map_vdso(&vdso_image_x32, true);
233 	}
234 #endif
235 
236 	return load_vdso32();
237 }
238 #endif
239 #else
arch_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)240 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
241 {
242 	return load_vdso32();
243 }
244 #endif
245 
246 #ifdef CONFIG_X86_64
vdso_setup(char * s)247 static __init int vdso_setup(char *s)
248 {
249 	vdso64_enabled = simple_strtoul(s, NULL, 0);
250 	return 0;
251 }
252 __setup("vdso=", vdso_setup);
253 #endif
254