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
19 unsigned int __read_mostly vdso_enabled = 1;
20
21 extern char vdso_start[], vdso_end[];
22 extern unsigned short vdso_sync_cpuid;
23
24 extern struct page *vdso_pages[];
25 static unsigned vdso_size;
26
27 #ifdef CONFIG_X86_X32_ABI
28 extern char vdsox32_start[], vdsox32_end[];
29 extern struct page *vdsox32_pages[];
30 static unsigned vdsox32_size;
31
patch_vdsox32(void * vdso,size_t len)32 static void __init patch_vdsox32(void *vdso, size_t len)
33 {
34 Elf32_Ehdr *hdr = vdso;
35 Elf32_Shdr *sechdrs, *alt_sec = 0;
36 char *secstrings;
37 void *alt_data;
38 int i;
39
40 BUG_ON(len < sizeof(Elf32_Ehdr));
41 BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
42
43 sechdrs = (void *)hdr + hdr->e_shoff;
44 secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
45
46 for (i = 1; i < hdr->e_shnum; i++) {
47 Elf32_Shdr *shdr = &sechdrs[i];
48 if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
49 alt_sec = shdr;
50 goto found;
51 }
52 }
53
54 /* If we get here, it's probably a bug. */
55 pr_warning("patch_vdsox32: .altinstructions not found\n");
56 return; /* nothing to patch */
57
58 found:
59 alt_data = (void *)hdr + alt_sec->sh_offset;
60 apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
61 }
62 #endif
63
patch_vdso64(void * vdso,size_t len)64 static void __init patch_vdso64(void *vdso, size_t len)
65 {
66 Elf64_Ehdr *hdr = vdso;
67 Elf64_Shdr *sechdrs, *alt_sec = 0;
68 char *secstrings;
69 void *alt_data;
70 int i;
71
72 BUG_ON(len < sizeof(Elf64_Ehdr));
73 BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
74
75 sechdrs = (void *)hdr + hdr->e_shoff;
76 secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
77
78 for (i = 1; i < hdr->e_shnum; i++) {
79 Elf64_Shdr *shdr = &sechdrs[i];
80 if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
81 alt_sec = shdr;
82 goto found;
83 }
84 }
85
86 /* If we get here, it's probably a bug. */
87 pr_warning("patch_vdso64: .altinstructions not found\n");
88 return; /* nothing to patch */
89
90 found:
91 alt_data = (void *)hdr + alt_sec->sh_offset;
92 apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
93 }
94
init_vdso(void)95 static int __init init_vdso(void)
96 {
97 int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
98 int i;
99
100 patch_vdso64(vdso_start, vdso_end - vdso_start);
101
102 vdso_size = npages << PAGE_SHIFT;
103 for (i = 0; i < npages; i++)
104 vdso_pages[i] = virt_to_page(vdso_start + i*PAGE_SIZE);
105
106 #ifdef CONFIG_X86_X32_ABI
107 patch_vdsox32(vdsox32_start, vdsox32_end - vdsox32_start);
108 npages = (vdsox32_end - vdsox32_start + PAGE_SIZE - 1) / PAGE_SIZE;
109 vdsox32_size = npages << PAGE_SHIFT;
110 for (i = 0; i < npages; i++)
111 vdsox32_pages[i] = virt_to_page(vdsox32_start + i*PAGE_SIZE);
112 #endif
113
114 return 0;
115 }
116 subsys_initcall(init_vdso);
117
118 struct linux_binprm;
119
120 /* Put the vdso above the (randomized) stack with another randomized offset.
121 This way there is no hole in the middle of address space.
122 To save memory make sure it is still in the same PTE as the stack top.
123 This doesn't give that many random bits */
vdso_addr(unsigned long start,unsigned len)124 static unsigned long vdso_addr(unsigned long start, unsigned len)
125 {
126 unsigned long addr, end;
127 unsigned offset;
128 end = (start + PMD_SIZE - 1) & PMD_MASK;
129 if (end >= TASK_SIZE_MAX)
130 end = TASK_SIZE_MAX;
131 end -= len;
132 /* This loses some more bits than a modulo, but is cheaper */
133 offset = get_random_int() & (PTRS_PER_PTE - 1);
134 addr = start + (offset << PAGE_SHIFT);
135 if (addr >= end)
136 addr = end;
137
138 /*
139 * page-align it here so that get_unmapped_area doesn't
140 * align it wrongfully again to the next page. addr can come in 4K
141 * unaligned here as a result of stack start randomization.
142 */
143 addr = PAGE_ALIGN(addr);
144 addr = align_addr(addr, NULL, ALIGN_VDSO);
145
146 return addr;
147 }
148
149 /* Setup a VMA at program startup for the vsyscall page.
150 Not called for compat tasks */
setup_additional_pages(struct linux_binprm * bprm,int uses_interp,struct page ** pages,unsigned size)151 static int setup_additional_pages(struct linux_binprm *bprm,
152 int uses_interp,
153 struct page **pages,
154 unsigned size)
155 {
156 struct mm_struct *mm = current->mm;
157 unsigned long addr;
158 int ret;
159
160 if (!vdso_enabled)
161 return 0;
162
163 down_write(&mm->mmap_sem);
164 addr = vdso_addr(mm->start_stack, size);
165 addr = get_unmapped_area(NULL, addr, size, 0, 0);
166 if (IS_ERR_VALUE(addr)) {
167 ret = addr;
168 goto up_fail;
169 }
170
171 current->mm->context.vdso = (void *)addr;
172
173 ret = install_special_mapping(mm, addr, size,
174 VM_READ|VM_EXEC|
175 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
176 pages);
177 if (ret) {
178 current->mm->context.vdso = NULL;
179 goto up_fail;
180 }
181
182 up_fail:
183 up_write(&mm->mmap_sem);
184 return ret;
185 }
186
arch_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)187 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
188 {
189 return setup_additional_pages(bprm, uses_interp, vdso_pages,
190 vdso_size);
191 }
192
193 #ifdef CONFIG_X86_X32_ABI
x32_setup_additional_pages(struct linux_binprm * bprm,int uses_interp)194 int x32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
195 {
196 return setup_additional_pages(bprm, uses_interp, vdsox32_pages,
197 vdsox32_size);
198 }
199 #endif
200
vdso_setup(char * s)201 static __init int vdso_setup(char *s)
202 {
203 vdso_enabled = simple_strtoul(s, NULL, 0);
204 return 0;
205 }
206 __setup("vdso=", vdso_setup);
207