1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * functions to patch RO kernel text during runtime
4 *
5 * Copyright (c) 2019 Sven Schnelle <svens@stackframe.org>
6 */
7
8 #include <linux/kernel.h>
9 #include <linux/spinlock.h>
10 #include <linux/kprobes.h>
11 #include <linux/mm.h>
12 #include <linux/stop_machine.h>
13
14 #include <asm/cacheflush.h>
15 #include <asm/fixmap.h>
16 #include <asm/patch.h>
17
18 struct patch {
19 void *addr;
20 u32 *insn;
21 unsigned int len;
22 };
23
24 static DEFINE_RAW_SPINLOCK(patch_lock);
25
patch_map(void * addr,int fixmap,unsigned long * flags,int * need_unmap)26 static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags,
27 int *need_unmap)
28 {
29 unsigned long uintaddr = (uintptr_t) addr;
30 bool module = !core_kernel_text(uintaddr);
31 struct page *page;
32
33 *need_unmap = 0;
34 if (module && IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
35 page = vmalloc_to_page(addr);
36 else if (!module && IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
37 page = virt_to_page(addr);
38 else
39 return addr;
40
41 *need_unmap = 1;
42 set_fixmap(fixmap, page_to_phys(page));
43 if (flags)
44 raw_spin_lock_irqsave(&patch_lock, *flags);
45 else
46 __acquire(&patch_lock);
47
48 return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
49 }
50
patch_unmap(int fixmap,unsigned long * flags)51 static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
52 {
53 clear_fixmap(fixmap);
54
55 if (flags)
56 raw_spin_unlock_irqrestore(&patch_lock, *flags);
57 else
58 __release(&patch_lock);
59 }
60
__patch_text_multiple(void * addr,u32 * insn,unsigned int len)61 void __kprobes __patch_text_multiple(void *addr, u32 *insn, unsigned int len)
62 {
63 unsigned long start = (unsigned long)addr;
64 unsigned long end = (unsigned long)addr + len;
65 unsigned long flags;
66 u32 *p, *fixmap;
67 int mapped;
68
69 /* Make sure we don't have any aliases in cache */
70 flush_kernel_vmap_range(addr, len);
71 flush_icache_range(start, end);
72
73 p = fixmap = patch_map(addr, FIX_TEXT_POKE0, &flags, &mapped);
74
75 while (len >= 4) {
76 *p++ = *insn++;
77 addr += sizeof(u32);
78 len -= sizeof(u32);
79 if (len && offset_in_page(addr) == 0) {
80 /*
81 * We're crossing a page boundary, so
82 * need to remap
83 */
84 flush_kernel_vmap_range((void *)fixmap,
85 (p-fixmap) * sizeof(*p));
86 if (mapped)
87 patch_unmap(FIX_TEXT_POKE0, &flags);
88 p = fixmap = patch_map(addr, FIX_TEXT_POKE0, &flags,
89 &mapped);
90 }
91 }
92
93 flush_kernel_vmap_range((void *)fixmap, (p-fixmap) * sizeof(*p));
94 if (mapped)
95 patch_unmap(FIX_TEXT_POKE0, &flags);
96 flush_icache_range(start, end);
97 }
98
__patch_text(void * addr,u32 insn)99 void __kprobes __patch_text(void *addr, u32 insn)
100 {
101 __patch_text_multiple(addr, &insn, sizeof(insn));
102 }
103
patch_text_stop_machine(void * data)104 static int __kprobes patch_text_stop_machine(void *data)
105 {
106 struct patch *patch = data;
107
108 __patch_text_multiple(patch->addr, patch->insn, patch->len);
109 return 0;
110 }
111
patch_text(void * addr,unsigned int insn)112 void __kprobes patch_text(void *addr, unsigned int insn)
113 {
114 struct patch patch = {
115 .addr = addr,
116 .insn = &insn,
117 .len = sizeof(insn),
118 };
119
120 stop_machine_cpuslocked(patch_text_stop_machine, &patch, NULL);
121 }
122
patch_text_multiple(void * addr,u32 * insn,unsigned int len)123 void __kprobes patch_text_multiple(void *addr, u32 *insn, unsigned int len)
124 {
125
126 struct patch patch = {
127 .addr = addr,
128 .insn = insn,
129 .len = len
130 };
131
132 stop_machine_cpuslocked(patch_text_stop_machine, &patch, NULL);
133 }
134
