1/*
2 * arch/arm/probes/kprobes/checkers-thumb.c
3 *
4 * Copyright (C) 2014 Huawei Inc.
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13 * General Public License for more details.
14 */
15
16#include <linux/kernel.h>
17#include "../decode.h"
18#include "../decode-thumb.h"
19#include "checkers.h"
20
21static enum probes_insn __kprobes t32_check_stack(probes_opcode_t insn,
22		struct arch_probes_insn *asi,
23		const struct decode_header *h)
24{
25	/*
26	 * PROBES_T32_LDMSTM, PROBES_T32_LDRDSTRD and PROBES_T32_LDRSTR
27	 * may get here. Simply mark all normal insns as STACK_USE_NONE.
28	 */
29	static const union decode_item table[] = {
30
31		/*
32		 * First, filter out all ldr insns to make our life easier.
33		 * Following load insns may come here:
34		 * LDM, LDRD, LDR.
35		 * In T32 encoding, bit 20 is enough for distinguishing
36		 * load and store. All load insns have this bit set, when
37		 * all store insns have this bit clear.
38		 */
39		DECODE_CUSTOM	(0x00100000, 0x00100000, STACK_USE_NONE),
40
41		/*
42		 * Mark all 'STR{,B,H}, Rt, [Rn, Rm]' as STACK_USE_UNKNOWN
43		 * if Rn or Rm is SP. T32 doesn't encode STRD.
44		 */
45		/*                                 xx | Rn | Rt |         | Rm |*/
46		/* STR (register)	1111 1000 0100 xxxx xxxx 0000 00xx xxxx */
47		/* STRB (register)	1111 1000 0000 xxxx xxxx 0000 00xx xxxx */
48		/* STRH (register)	1111 1000 0010 xxxx xxxx 0000 00xx xxxx */
49		/* INVALID INSN		1111 1000 0110 xxxx xxxx 0000 00xx xxxx */
50		/* By Introducing INVALID INSN, bit 21 and 22 can be ignored. */
51		DECODE_OR	(0xff9f0fc0, 0xf80d0000),
52		DECODE_CUSTOM	(0xff900fcf, 0xf800000d, STACK_USE_UNKNOWN),
53
54
55		/*                                 xx | Rn | Rt | PUW|   imm8  |*/
56		/* STR (imm 8)		1111 1000 0100 1101 xxxx 110x xxxx xxxx */
57		/* STRB (imm 8)		1111 1000 0000 1101 xxxx 110x xxxx xxxx */
58		/* STRH (imm 8)		1111 1000 0010 1101 xxxx 110x xxxx xxxx */
59		/* INVALID INSN		1111 1000 0110 1101 xxxx 110x xxxx xxxx */
60		/* Only consider U == 0 and P == 1: strx rx, [sp, #-<imm>] */
61		DECODE_CUSTOM	(0xff9f0e00, 0xf80d0c00, STACK_USE_FIXED_0XX),
62
63		/* For STR{,B,H} (imm 12), offset is always positive, so ignore them. */
64
65		/*                              P U W | Rn | Rt | Rt2|   imm8  |*/
66		/* STRD (immediate)	1110 1001 01x0 1101 xxxx xxxx xxxx xxxx */
67		/*
68		 * Only consider U == 0 and P == 1.
69		 * Also note that STRD in T32 encoding is special:
70		 * imm = ZeroExtend(imm8:'00', 32)
71		 */
72		DECODE_CUSTOM	(0xffdf0000, 0xe94d0000, STACK_USE_T32STRD),
73
74		/*                                    | Rn | */
75		/* STMDB		1110 1001 00x0 1101 xxxx xxxx xxxx xxxx */
76		DECODE_CUSTOM	(0xffdf0000, 0xe90d0000, STACK_USE_STMDX),
77
78		/* fall through */
79		DECODE_CUSTOM	(0, 0, STACK_USE_NONE),
80		DECODE_END
81	};
82
83	return probes_decode_insn(insn, asi, table, false, false, stack_check_actions, NULL);
84}
85
86const struct decode_checker t32_stack_checker[NUM_PROBES_T32_ACTIONS] = {
87	[PROBES_T32_LDMSTM] = {.checker = t32_check_stack},
88	[PROBES_T32_LDRDSTRD] = {.checker = t32_check_stack},
89	[PROBES_T32_LDRSTR] = {.checker = t32_check_stack},
90};
91
92/*
93 * See following comments. This insn must be 'push'.
94 */
95static enum probes_insn __kprobes t16_check_stack(probes_opcode_t insn,
96		struct arch_probes_insn *asi,
97		const struct decode_header *h)
98{
99	unsigned int reglist = insn & 0x1ff;
100	asi->stack_space = hweight32(reglist) * 4;
101	return INSN_GOOD;
102}
103
104/*
105 * T16 encoding is simple: only the 'push' insn can need extra stack space.
106 * Other insns, like str, can only use r0-r7 as Rn.
107 */
108const struct decode_checker t16_stack_checker[NUM_PROBES_T16_ACTIONS] = {
109	[PROBES_T16_PUSH] = {.checker = t16_check_stack},
110};
111