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/bpf.h>
9#include <linux/cfi_types.h>
10#include <linux/cfi.h>
11
12bool cfi_warn __ro_after_init = IS_ENABLED(CONFIG_CFI_PERMISSIVE);
13
14enum bug_trap_type report_cfi_failure(struct pt_regs *regs, unsigned long addr,
15 unsigned long *target, u32 type)
16{
17 if (target)
18 pr_err("CFI failure at %pS (target: %pS; expected type: 0x%08x)\n",
19 (void *)addr, (void *)*target, type);
20 else
21 pr_err("CFI failure at %pS (no target information)\n",
22 (void *)addr);
23
24 if (cfi_warn) {
25 __warn(NULL, line: 0, caller: (void *)addr, taint: 0, regs, NULL);
26 return BUG_TRAP_TYPE_WARN;
27 }
28
29 return BUG_TRAP_TYPE_BUG;
30}
31
32/*
33 * Declare two non-existent functions with types that match bpf_func_t and
34 * bpf_callback_t pointers, and use DEFINE_CFI_TYPE to define type hash
35 * variables for each function type. The cfi_bpf_* variables are used by
36 * arch-specific BPF JIT implementations to ensure indirectly callable JIT
37 * code has matching CFI type hashes.
38 */
39extern typeof(*(bpf_func_t)0) __bpf_prog_runX;
40DEFINE_CFI_TYPE(cfi_bpf_hash, __bpf_prog_runX);
41
42extern typeof(*(bpf_callback_t)0) __bpf_callback_fn;
43DEFINE_CFI_TYPE(cfi_bpf_subprog_hash, __bpf_callback_fn);
44
45#ifdef CONFIG_ARCH_USES_CFI_TRAPS
46static inline unsigned long trap_address(s32 *p)
47{
48 return (unsigned long)((long)p + (long)*p);
49}
50
51static bool is_trap(unsigned long addr, s32 *start, s32 *end)
52{
53 s32 *p;
54
55 for (p = start; p < end; ++p) {
56 if (trap_address(p) == addr)
57 return true;
58 }
59
60 return false;
61}
62
63#ifdef CONFIG_MODULES
64/* Populates `kcfi_trap(_end)?` fields in `struct module`. */
65void module_cfi_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
66 struct module *mod)
67{
68 char *secstrings;
69 unsigned int i;
70
71 mod->kcfi_traps = NULL;
72 mod->kcfi_traps_end = NULL;
73
74 secstrings = (char *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
75
76 for (i = 1; i < hdr->e_shnum; i++) {
77 if (strcmp(secstrings + sechdrs[i].sh_name, "__kcfi_traps"))
78 continue;
79
80 mod->kcfi_traps = (s32 *)sechdrs[i].sh_addr;
81 mod->kcfi_traps_end = (s32 *)(sechdrs[i].sh_addr + sechdrs[i].sh_size);
82 break;
83 }
84}
85
86static bool is_module_cfi_trap(unsigned long addr)
87{
88 struct module *mod;
89 bool found = false;
90
91 guard(rcu)();
92 mod = __module_address(addr);
93 if (mod)
94 found = is_trap(addr, mod->kcfi_traps, mod->kcfi_traps_end);
95
96 return found;
97}
98#else /* CONFIG_MODULES */
99static inline bool is_module_cfi_trap(unsigned long addr)
100{
101 return false;
102}
103#endif /* CONFIG_MODULES */
104
105extern s32 __start___kcfi_traps[];
106extern s32 __stop___kcfi_traps[];
107
108bool is_cfi_trap(unsigned long addr)
109{
110 if (is_trap(addr, __start___kcfi_traps, __stop___kcfi_traps))
111 return true;
112
113 return is_module_cfi_trap(addr);
114}
115#endif /* CONFIG_ARCH_USES_CFI_TRAPS */
116

source code of linux/kernel/cfi.c