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
report_cfi_failure(struct pt_regs * regs,unsigned long addr,unsigned long * target,u32 type)10 enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
11 unsigned long *target, u32 type)
12 {
13 if (target)
14 pr_err("CFI failure at %pS (target: %pS; expected type: 0x%08x)\n",
15 (void *)addr, (void *)*target, type);
16 else
17 pr_err("CFI failure at %pS (no target information)\n",
18 (void *)addr);
19
20 if (IS_ENABLED(CONFIG_CFI_PERMISSIVE)) {
21 __warn(NULL, 0, (void *)addr, 0, regs, NULL);
22 return BUG_TRAP_TYPE_WARN;
23 }
24
25 return BUG_TRAP_TYPE_BUG;
26 }
27
28 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
trap_address(s32 * p)29 static inline unsigned long trap_address(s32 *p)
30 {
31 return (unsigned long)((long)p + (long)*p);
32 }
33
is_trap(unsigned long addr,s32 * start,s32 * end)34 static bool is_trap(unsigned long addr, s32 *start, s32 *end)
35 {
36 s32 *p;
37
38 for (p = start; p < end; ++p) {
39 if (trap_address(p) == addr)
40 return true;
41 }
42
43 return false;
44 }
45
46 #ifdef CONFIG_MODULES
47 /* Populates `kcfi_trap(_end)?` fields in `struct module`. */
module_cfi_finalize(const Elf_Ehdr * hdr,const Elf_Shdr * sechdrs,struct module * mod)48 void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
49 struct module *mod)
50 {
51 char *secstrings;
52 unsigned int i;
53
54 mod->kcfi_traps = NULL;
55 mod->kcfi_traps_end = NULL;
56
57 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
58
59 for (i = 1; i < hdr->e_shnum; i++) {
60 if (strcmp(secstrings + sechdrs[i].sh_name, "__kcfi_traps"))
61 continue;
62
63 mod->kcfi_traps = (s32 *)sechdrs[i].sh_addr;
64 mod->kcfi_traps_end = (s32 *)(sechdrs[i].sh_addr + sechdrs[i].sh_size);
65 break;
66 }
67 }
68
is_module_cfi_trap(unsigned long addr)69 static bool is_module_cfi_trap(unsigned long addr)
70 {
71 struct module *mod;
72 bool found = false;
73
74 rcu_read_lock_sched_notrace();
75
76 mod = __module_address(addr);
77 if (mod)
78 found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end);
79
80 rcu_read_unlock_sched_notrace();
81
82 return found;
83 }
84 #else /* CONFIG_MODULES */
is_module_cfi_trap(unsigned long addr)85 static inline bool is_module_cfi_trap(unsigned long addr)
86 {
87 return false;
88 }
89 #endif /* CONFIG_MODULES */
90
91 extern s32 __start___kcfi_traps[];
92 extern s32 __stop___kcfi_traps[];
93
is_cfi_trap(unsigned long addr)94 bool is_cfi_trap(unsigned long addr)
95 {
96 if (is_trap(addr, __start___kcfi_traps, __stop___kcfi_traps))
97 return true;
98
99 return is_module_cfi_trap(addr);
100 }
101 #endif /* CONFIG_ARCH_USES_CFI_TRAPS */
102
