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
 10enum 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
 29static inline unsigned long trap_address(s32 *p)
 30{
 31	return (unsigned long)((long)p + (long)*p);
 32}
 33
 34static 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`. */
 48void 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
 69static 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 */
 85static inline bool is_module_cfi_trap(unsigned long addr)
 86{
 87	return false;
 88}
 89#endif /* CONFIG_MODULES */
 90
 91extern s32 __start___kcfi_traps[];
 92extern s32 __stop___kcfi_traps[];
 93
 94bool 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 */