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
18struct patch {
19	void *addr;
20	u32 *insn;
21	unsigned int len;
22};
23
24static DEFINE_RAW_SPINLOCK(patch_lock);
25
26static 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	raw_spin_lock_irqsave(&patch_lock, *flags);
44
45	return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
46}
47
48static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
49{
50	clear_fixmap(fixmap);
51
52	raw_spin_unlock_irqrestore(&patch_lock, *flags);
53}
54
55void __kprobes __patch_text_multiple(void *addr, u32 *insn, unsigned int len)
56{
57	unsigned long start = (unsigned long)addr;
58	unsigned long end = (unsigned long)addr + len;
59	unsigned long flags;
60	u32 *p, *fixmap;
61	int mapped;
62
63	/* Make sure we don't have any aliases in cache */
64	flush_kernel_dcache_range_asm(start, end);
65	flush_kernel_icache_range_asm(start, end);
66	flush_tlb_kernel_range(start, end);
67
68	p = fixmap = patch_map(addr, FIX_TEXT_POKE0, &flags, &mapped);
69
70	while (len >= 4) {
71		*p++ = *insn++;
72		addr += sizeof(u32);
73		len -= sizeof(u32);
74		if (len && offset_in_page(addr) == 0) {
75			/*
76			 * We're crossing a page boundary, so
77			 * need to remap
78			 */
79			flush_kernel_dcache_range_asm((unsigned long)fixmap,
80						      (unsigned long)p);
81			flush_tlb_kernel_range((unsigned long)fixmap,
82					       (unsigned long)p);
83			if (mapped)
84				patch_unmap(FIX_TEXT_POKE0, &flags);
85			p = fixmap = patch_map(addr, FIX_TEXT_POKE0, &flags,
86						&mapped);
87		}
88	}
89
90	flush_kernel_dcache_range_asm((unsigned long)fixmap, (unsigned long)p);
91	flush_tlb_kernel_range((unsigned long)fixmap, (unsigned long)p);
92	if (mapped)
93		patch_unmap(FIX_TEXT_POKE0, &flags);
94}
95
96void __kprobes __patch_text(void *addr, u32 insn)
97{
98	__patch_text_multiple(addr, &insn, sizeof(insn));
99}
100
101static int __kprobes patch_text_stop_machine(void *data)
102{
103	struct patch *patch = data;
104
105	__patch_text_multiple(patch->addr, patch->insn, patch->len);
106	return 0;
107}
108
109void __kprobes patch_text(void *addr, unsigned int insn)
110{
111	struct patch patch = {
112		.addr = addr,
113		.insn = &insn,
114		.len = sizeof(insn),
115	};
116
117	stop_machine_cpuslocked(patch_text_stop_machine, &patch, NULL);
118}
119
120void __kprobes patch_text_multiple(void *addr, u32 *insn, unsigned int len)
121{
122
123	struct patch patch = {
124		.addr = addr,
125		.insn = insn,
126		.len = len
127	};
128
129	stop_machine_cpuslocked(patch_text_stop_machine, &patch, NULL);
130}
131