1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  Copyright (c) 2022 Helge Deller <deller@gmx.de>
4  *
5  *  based on arch/s390/kernel/vdso.c which is
6  *  Copyright IBM Corp. 2008
7  *  Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
8  */
9 
10 #include <linux/kernel.h>
11 #include <linux/mm.h>
12 #include <linux/slab.h>
13 #include <linux/elf.h>
14 #include <linux/timekeeper_internal.h>
15 #include <linux/compat.h>
16 #include <linux/nsproxy.h>
17 #include <linux/time_namespace.h>
18 #include <linux/random.h>
19 
20 #include <asm/pgtable.h>
21 #include <asm/page.h>
22 #include <asm/sections.h>
23 #include <asm/vdso.h>
24 #include <asm/cacheflush.h>
25 
26 extern char vdso32_start, vdso32_end;
27 extern char vdso64_start, vdso64_end;
28 
vdso_mremap(const struct vm_special_mapping * sm,struct vm_area_struct * vma)29 static int vdso_mremap(const struct vm_special_mapping *sm,
30 		       struct vm_area_struct *vma)
31 {
32 	current->mm->context.vdso_base = vma->vm_start;
33 	return 0;
34 }
35 
36 #ifdef CONFIG_64BIT
37 static struct vm_special_mapping vdso64_mapping = {
38 	.name = "[vdso]",
39 	.mremap = vdso_mremap,
40 };
41 #endif
42 
43 static struct vm_special_mapping vdso32_mapping = {
44 	.name = "[vdso]",
45 	.mremap = vdso_mremap,
46 };
47 
48 /*
49  * This is called from binfmt_elf, we create the special vma for the
50  * vDSO and insert it into the mm struct tree
51  */
arch_setup_additional_pages(struct linux_binprm * bprm,int executable_stack)52 int arch_setup_additional_pages(struct linux_binprm *bprm,
53 				int executable_stack)
54 {
55 
56 	unsigned long vdso_text_start, vdso_text_len, map_base;
57 	struct vm_special_mapping *vdso_mapping;
58 	struct mm_struct *mm = current->mm;
59 	struct vm_area_struct *vma;
60 	int rc;
61 
62 	if (mmap_write_lock_killable(mm))
63 		return -EINTR;
64 
65 #ifdef CONFIG_64BIT
66 	if (!is_compat_task()) {
67 		vdso_text_len = &vdso64_end - &vdso64_start;
68 		vdso_mapping = &vdso64_mapping;
69 	} else
70 #endif
71 	{
72 		vdso_text_len = &vdso32_end - &vdso32_start;
73 		vdso_mapping = &vdso32_mapping;
74 	}
75 
76 	map_base = mm->mmap_base;
77 	if (current->flags & PF_RANDOMIZE)
78 		map_base -= get_random_u32_below(0x20) * PAGE_SIZE;
79 
80 	vdso_text_start = get_unmapped_area(NULL, map_base, vdso_text_len, 0, 0);
81 
82 	/* VM_MAYWRITE for COW so gdb can set breakpoints */
83 	vma = _install_special_mapping(mm, vdso_text_start, vdso_text_len,
84 				       VM_READ|VM_EXEC|
85 				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
86 				       vdso_mapping);
87 	if (IS_ERR(vma)) {
88 		do_munmap(mm, vdso_text_start, PAGE_SIZE, NULL);
89 		rc = PTR_ERR(vma);
90 	} else {
91 		current->mm->context.vdso_base = vdso_text_start;
92 		rc = 0;
93 	}
94 
95 	mmap_write_unlock(mm);
96 	return rc;
97 }
98 
vdso_setup_pages(void * start,void * end)99 static struct page ** __init vdso_setup_pages(void *start, void *end)
100 {
101 	int pages = (end - start) >> PAGE_SHIFT;
102 	struct page **pagelist;
103 	int i;
104 
105 	pagelist = kcalloc(pages + 1, sizeof(struct page *), GFP_KERNEL);
106 	if (!pagelist)
107 		panic("%s: Cannot allocate page list for VDSO", __func__);
108 	for (i = 0; i < pages; i++)
109 		pagelist[i] = virt_to_page(start + i * PAGE_SIZE);
110 	return pagelist;
111 }
112 
vdso_init(void)113 static int __init vdso_init(void)
114 {
115 #ifdef CONFIG_64BIT
116 	vdso64_mapping.pages = vdso_setup_pages(&vdso64_start, &vdso64_end);
117 #endif
118 	if (IS_ENABLED(CONFIG_COMPAT) || !IS_ENABLED(CONFIG_64BIT))
119 		vdso32_mapping.pages = vdso_setup_pages(&vdso32_start, &vdso32_end);
120 	return 0;
121 }
122 arch_initcall(vdso_init);
123