1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * Clang Control Flow Integrity (CFI) support.
 4 *
 5 * Copyright (C) 2022 Google LLC
 6 */
 7#include <asm/cfi.h>
 8#include <asm/insn.h>
 9#include <asm/insn-eval.h>
10#include <linux/string.h>
11
12/*
13 * Returns the target address and the expected type when regs->ip points
14 * to a compiler-generated CFI trap.
15 */
16static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
17			    u32 *type)
18{
19	char buffer[MAX_INSN_SIZE];
20	struct insn insn;
21	int offset = 0;
22
23	*target = *type = 0;
24
25	/*
26	 * The compiler generates the following instruction sequence
27	 * for indirect call checks:
28	 *
29	 *   movl    -<id>, %r10d       ; 6 bytes
30	 *   addl    -4(%reg), %r10d    ; 4 bytes
31	 *   je      .Ltmp1             ; 2 bytes
32	 *   ud2                        ; <- regs->ip
33	 *   .Ltmp1:
34	 *
35	 * We can decode the expected type and the target address from the
36	 * movl/addl instructions.
37	 */
38	if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 12, MAX_INSN_SIZE))
39		return false;
40	if (insn_decode_kernel(&insn, &buffer[offset]))
41		return false;
42	if (insn.opcode.value != 0xBA)
43		return false;
44
45	*type = -(u32)insn.immediate.value;
46
47	if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 6, MAX_INSN_SIZE))
48		return false;
49	if (insn_decode_kernel(&insn, &buffer[offset]))
50		return false;
51	if (insn.opcode.value != 0x3)
52		return false;
53
54	/* Read the target address from the register. */
55	offset = insn_get_modrm_rm_off(&insn, regs);
56	if (offset < 0)
57		return false;
58
59	*target = *(unsigned long *)((void *)regs + offset);
60
61	return true;
62}
63
64/*
65 * Checks if a ud2 trap is because of a CFI failure, and handles the trap
66 * if needed. Returns a bug_trap_type value similarly to report_bug.
67 */
68enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
69{
70	unsigned long target;
71	u32 type;
72
73	if (!is_cfi_trap(regs->ip))
74		return BUG_TRAP_TYPE_NONE;
75
76	if (!decode_cfi_insn(regs, &target, &type))
77		return report_cfi_failure_noaddr(regs, regs->ip);
78
79	return report_cfi_failure(regs, regs->ip, &target, type);
80}
81
82/*
83 * Ensure that __kcfi_typeid_ symbols are emitted for functions that may
84 * not be indirectly called with all configurations.
85 */
86__ADDRESSABLE(__memcpy)