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/text-patching.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}