1 /*
2 * livepatch.c - x86-specific Kernel Live Patching Core
3 *
4 * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
5 * Copyright (C) 2014 SUSE
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version 2
10 * of the License, or (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, see <http://www.gnu.org/licenses/>.
19 */
20
21 #include <linux/module.h>
22 #include <linux/uaccess.h>
23 #include <asm/cacheflush.h>
24 #include <asm/page_types.h>
25 #include <asm/elf.h>
26 #include <asm/livepatch.h>
27
28 /**
29 * klp_write_module_reloc() - write a relocation in a module
30 * @mod: module in which the section to be modified is found
31 * @type: ELF relocation type (see asm/elf.h)
32 * @loc: address that the relocation should be written to
33 * @value: relocation value (sym address + addend)
34 *
35 * This function writes a relocation to the specified location for
36 * a particular module.
37 */
klp_write_module_reloc(struct module * mod,unsigned long type,unsigned long loc,unsigned long value)38 int klp_write_module_reloc(struct module *mod, unsigned long type,
39 unsigned long loc, unsigned long value)
40 {
41 int ret, numpages, size = 4;
42 bool readonly;
43 unsigned long val;
44 unsigned long core = (unsigned long)mod->module_core;
45 unsigned long core_ro_size = mod->core_ro_size;
46 unsigned long core_size = mod->core_size;
47
48 switch (type) {
49 case R_X86_64_NONE:
50 return 0;
51 case R_X86_64_64:
52 val = value;
53 size = 8;
54 break;
55 case R_X86_64_32:
56 val = (u32)value;
57 break;
58 case R_X86_64_32S:
59 val = (s32)value;
60 break;
61 case R_X86_64_PC32:
62 val = (u32)(value - loc);
63 break;
64 default:
65 /* unsupported relocation type */
66 return -EINVAL;
67 }
68
69 if (loc < core || loc >= core + core_size)
70 /* loc does not point to any symbol inside the module */
71 return -EINVAL;
72
73 if (loc < core + core_ro_size)
74 readonly = true;
75 else
76 readonly = false;
77
78 /* determine if the relocation spans a page boundary */
79 numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
80
81 if (readonly)
82 set_memory_rw(loc & PAGE_MASK, numpages);
83
84 ret = probe_kernel_write((void *)loc, &val, size);
85
86 if (readonly)
87 set_memory_ro(loc & PAGE_MASK, numpages);
88
89 return ret;
90 }
91