1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Clang Control Flow Integrity (CFI) error handling.
4 *
5 * Copyright (C) 2022 Google LLC
6 */
7
8 #include <linux/cfi.h>
9
10 bool cfi_warn __ro_after_init = IS_ENABLED(CONFIG_CFI_PERMISSIVE);
11
report_cfi_failure(struct pt_regs * regs,unsigned long addr,unsigned long * target,u32 type)12 enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
13 unsigned long *target, u32 type)
14 {
15 if (target)
16 pr_err("CFI failure at %pS (target: %pS; expected type: 0x%08x)\n",
17 (void *)addr, (void *)*target, type);
18 else
19 pr_err("CFI failure at %pS (no target information)\n",
20 (void *)addr);
21
22 if (cfi_warn) {
23 __warn(NULL, 0, (void *)addr, 0, regs, NULL);
24 return BUG_TRAP_TYPE_WARN;
25 }
26
27 return BUG_TRAP_TYPE_BUG;
28 }
29
30 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
trap_address(s32 * p)31 static inline unsigned long trap_address(s32 *p)
32 {
33 return (unsigned long)((long)p + (long)*p);
34 }
35
is_trap(unsigned long addr,s32 * start,s32 * end)36 static bool is_trap(unsigned long addr, s32 *start, s32 *end)
37 {
38 s32 *p;
39
40 for (p = start; p < end; ++p) {
41 if (trap_address(p) == addr)
42 return true;
43 }
44
45 return false;
46 }
47
48 #ifdef CONFIG_MODULES
49 /* Populates `kcfi_trap(_end)?` fields in `struct module`. */
module_cfi_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)50 void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
51 struct module *mod)
52 {
53 char *secstrings;
54 unsigned int i;
55
56 mod->kcfi_traps = NULL;
57 mod->kcfi_traps_end = NULL;
58
59 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
60
61 for (i = 1; i < hdr->e_shnum; i++) {
62 if (strcmp(secstrings + sechdrs[i].sh_name, "__kcfi_traps"))
63 continue;
64
65 mod->kcfi_traps = (s32 *)sechdrs[i].sh_addr;
66 mod->kcfi_traps_end = (s32 *)(sechdrs[i].sh_addr + sechdrs[i].sh_size);
67 break;
68 }
69 }
70
is_module_cfi_trap(unsigned long addr)71 static bool is_module_cfi_trap(unsigned long addr)
72 {
73 struct module *mod;
74 bool found = false;
75
76 guard(rcu)();
77 mod = __module_address(addr);
78 if (mod)
79 found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end);
80
81 return found;
82 }
83 #else /* CONFIG_MODULES */
is_module_cfi_trap(unsigned long addr)84 static inline bool is_module_cfi_trap(unsigned long addr)
85 {
86 return false;
87 }
88 #endif /* CONFIG_MODULES */
89
90 extern s32 __start___kcfi_traps[];
91 extern s32 __stop___kcfi_traps[];
92
is_cfi_trap(unsigned long addr)93 bool is_cfi_trap(unsigned long addr)
94 {
95 if (is_trap(addr, __start___kcfi_traps, __stop___kcfi_traps))
96 return true;
97
98 return is_module_cfi_trap(addr);
99 }
100 #endif /* CONFIG_ARCH_USES_CFI_TRAPS */
101