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1/*
2 * arch/arm/kernel/kprobes-common.c
3 *
4 * Copyright (C) 2011 Jon Medhurst <tixy@yxit.co.uk>.
5 *
6 * Some contents moved here from arch/arm/include/asm/kprobes-arm.c which is
7 * Copyright (C) 2006, 2007 Motorola Inc.
8 *
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License version 2 as
11 * published by the Free Software Foundation.
12 */
13
14#include <linux/kernel.h>
15#include <linux/kprobes.h>
16#include <asm/system_info.h>
17
18#include "kprobes.h"
19
20
21#ifndef find_str_pc_offset
22
23/*
24 * For STR and STM instructions, an ARM core may choose to use either
25 * a +8 or a +12 displacement from the current instruction's address.
26 * Whichever value is chosen for a given core, it must be the same for
27 * both instructions and may not change. This function measures it.
28 */
29
30int str_pc_offset;
31
32void __init find_str_pc_offset(void)
33{
34 int addr, scratch, ret;
35
36 __asm__ (
37 "sub %[ret], pc, #4 \n\t"
38 "str pc, %[addr] \n\t"
39 "ldr %[scr], %[addr] \n\t"
40 "sub %[ret], %[scr], %[ret] \n\t"
41 : [ret] "=r" (ret), [scr] "=r" (scratch), [addr] "+m" (addr));
42
43 str_pc_offset = ret;
44}
45
46#endif /* !find_str_pc_offset */
47
48
49#ifndef test_load_write_pc_interworking
50
51bool load_write_pc_interworks;
52
53void __init test_load_write_pc_interworking(void)
54{
55 int arch = cpu_architecture();
56 BUG_ON(arch == CPU_ARCH_UNKNOWN);
57 load_write_pc_interworks = arch >= CPU_ARCH_ARMv5T;
58}
59
60#endif /* !test_load_write_pc_interworking */
61
62
63#ifndef test_alu_write_pc_interworking
64
65bool alu_write_pc_interworks;
66
67void __init test_alu_write_pc_interworking(void)
68{
69 int arch = cpu_architecture();
70 BUG_ON(arch == CPU_ARCH_UNKNOWN);
71 alu_write_pc_interworks = arch >= CPU_ARCH_ARMv7;
72}
73
74#endif /* !test_alu_write_pc_interworking */
75
76
77void __init arm_kprobe_decode_init(void)
78{
79 find_str_pc_offset();
80 test_load_write_pc_interworking();
81 test_alu_write_pc_interworking();
82}
83
84
85static unsigned long __kprobes __check_eq(unsigned long cpsr)
86{
87 return cpsr & PSR_Z_BIT;
88}
89
90static unsigned long __kprobes __check_ne(unsigned long cpsr)
91{
92 return (~cpsr) & PSR_Z_BIT;
93}
94
95static unsigned long __kprobes __check_cs(unsigned long cpsr)
96{
97 return cpsr & PSR_C_BIT;
98}
99
100static unsigned long __kprobes __check_cc(unsigned long cpsr)
101{
102 return (~cpsr) & PSR_C_BIT;
103}
104
105static unsigned long __kprobes __check_mi(unsigned long cpsr)
106{
107 return cpsr & PSR_N_BIT;
108}
109
110static unsigned long __kprobes __check_pl(unsigned long cpsr)
111{
112 return (~cpsr) & PSR_N_BIT;
113}
114
115static unsigned long __kprobes __check_vs(unsigned long cpsr)
116{
117 return cpsr & PSR_V_BIT;
118}
119
120static unsigned long __kprobes __check_vc(unsigned long cpsr)
121{
122 return (~cpsr) & PSR_V_BIT;
123}
124
125static unsigned long __kprobes __check_hi(unsigned long cpsr)
126{
127 cpsr &= ~(cpsr >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */
128 return cpsr & PSR_C_BIT;
129}
130
131static unsigned long __kprobes __check_ls(unsigned long cpsr)
132{
133 cpsr &= ~(cpsr >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */
134 return (~cpsr) & PSR_C_BIT;
135}
136
137static unsigned long __kprobes __check_ge(unsigned long cpsr)
138{
139 cpsr ^= (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
140 return (~cpsr) & PSR_N_BIT;
141}
142
143static unsigned long __kprobes __check_lt(unsigned long cpsr)
144{
145 cpsr ^= (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
146 return cpsr & PSR_N_BIT;
147}
148
149static unsigned long __kprobes __check_gt(unsigned long cpsr)
150{
151 unsigned long temp = cpsr ^ (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
152 temp |= (cpsr << 1); /* PSR_N_BIT |= PSR_Z_BIT */
153 return (~temp) & PSR_N_BIT;
154}
155
156static unsigned long __kprobes __check_le(unsigned long cpsr)
157{
158 unsigned long temp = cpsr ^ (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
159 temp |= (cpsr << 1); /* PSR_N_BIT |= PSR_Z_BIT */
160 return temp & PSR_N_BIT;
161}
162
163static unsigned long __kprobes __check_al(unsigned long cpsr)
164{
165 return true;
166}
167
168kprobe_check_cc * const kprobe_condition_checks[16] = {
169 &__check_eq, &__check_ne, &__check_cs, &__check_cc,
170 &__check_mi, &__check_pl, &__check_vs, &__check_vc,
171 &__check_hi, &__check_ls, &__check_ge, &__check_lt,
172 &__check_gt, &__check_le, &__check_al, &__check_al
173};
174
175
176void __kprobes kprobe_simulate_nop(struct kprobe *p, struct pt_regs *regs)
177{
178}
179
180void __kprobes kprobe_emulate_none(struct kprobe *p, struct pt_regs *regs)
181{
182 p->ainsn.insn_fn();
183}
184
185static void __kprobes simulate_ldm1stm1(struct kprobe *p, struct pt_regs *regs)
186{
187 kprobe_opcode_t insn = p->opcode;
188 int rn = (insn >> 16) & 0xf;
189 int lbit = insn & (1 << 20);
190 int wbit = insn & (1 << 21);
191 int ubit = insn & (1 << 23);
192 int pbit = insn & (1 << 24);
193 long *addr = (long *)regs->uregs[rn];
194 int reg_bit_vector;
195 int reg_count;
196
197 reg_count = 0;
198 reg_bit_vector = insn & 0xffff;
199 while (reg_bit_vector) {
200 reg_bit_vector &= (reg_bit_vector - 1);
201 ++reg_count;
202 }
203
204 if (!ubit)
205 addr -= reg_count;
206 addr += (!pbit == !ubit);
207
208 reg_bit_vector = insn & 0xffff;
209 while (reg_bit_vector) {
210 int reg = __ffs(reg_bit_vector);
211 reg_bit_vector &= (reg_bit_vector - 1);
212 if (lbit)
213 regs->uregs[reg] = *addr++;
214 else
215 *addr++ = regs->uregs[reg];
216 }
217
218 if (wbit) {
219 if (!ubit)
220 addr -= reg_count;
221 addr -= (!pbit == !ubit);
222 regs->uregs[rn] = (long)addr;
223 }
224}
225
226static void __kprobes simulate_stm1_pc(struct kprobe *p, struct pt_regs *regs)
227{
228 regs->ARM_pc = (long)p->addr + str_pc_offset;
229 simulate_ldm1stm1(p, regs);
230 regs->ARM_pc = (long)p->addr + 4;
231}
232
233static void __kprobes simulate_ldm1_pc(struct kprobe *p, struct pt_regs *regs)
234{
235 simulate_ldm1stm1(p, regs);
236 load_write_pc(regs->ARM_pc, regs);
237}
238
239static void __kprobes
240emulate_generic_r0_12_noflags(struct kprobe *p, struct pt_regs *regs)
241{
242 register void *rregs asm("r1") = regs;
243 register void *rfn asm("lr") = p->ainsn.insn_fn;
244
245 __asm__ __volatile__ (
246 "stmdb sp!, {%[regs], r11} \n\t"
247 "ldmia %[regs], {r0-r12} \n\t"
248#if __LINUX_ARM_ARCH__ >= 6
249 "blx %[fn] \n\t"
250#else
251 "str %[fn], [sp, #-4]! \n\t"
252 "adr lr, 1f \n\t"
253 "ldr pc, [sp], #4 \n\t"
254 "1: \n\t"
255#endif
256 "ldr lr, [sp], #4 \n\t" /* lr = regs */
257 "stmia lr, {r0-r12} \n\t"
258 "ldr r11, [sp], #4 \n\t"
259 : [regs] "=r" (rregs), [fn] "=r" (rfn)
260 : "0" (rregs), "1" (rfn)
261 : "r0", "r2", "r3", "r4", "r5", "r6", "r7",
262 "r8", "r9", "r10", "r12", "memory", "cc"
263 );
264}
265
266static void __kprobes
267emulate_generic_r2_14_noflags(struct kprobe *p, struct pt_regs *regs)
268{
269 emulate_generic_r0_12_noflags(p, (struct pt_regs *)(regs->uregs+2));
270}
271
272static void __kprobes
273emulate_ldm_r3_15(struct kprobe *p, struct pt_regs *regs)
274{
275 emulate_generic_r0_12_noflags(p, (struct pt_regs *)(regs->uregs+3));
276 load_write_pc(regs->ARM_pc, regs);
277}
278
279enum kprobe_insn __kprobes
280kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_specific_insn *asi)
281{
282 kprobe_insn_handler_t *handler = 0;
283 unsigned reglist = insn & 0xffff;
284 int is_ldm = insn & 0x100000;
285 int rn = (insn >> 16) & 0xf;
286
287 if (rn <= 12 && (reglist & 0xe000) == 0) {
288 /* Instruction only uses registers in the range R0..R12 */
289 handler = emulate_generic_r0_12_noflags;
290
291 } else if (rn >= 2 && (reglist & 0x8003) == 0) {
292 /* Instruction only uses registers in the range R2..R14 */
293 rn -= 2;
294 reglist >>= 2;
295 handler = emulate_generic_r2_14_noflags;
296
297 } else if (rn >= 3 && (reglist & 0x0007) == 0) {
298 /* Instruction only uses registers in the range R3..R15 */
299 if (is_ldm && (reglist & 0x8000)) {
300 rn -= 3;
301 reglist >>= 3;
302 handler = emulate_ldm_r3_15;
303 }
304 }
305
306 if (handler) {
307 /* We can emulate the instruction in (possibly) modified form */
308 asi->insn[0] = (insn & 0xfff00000) | (rn << 16) | reglist;
309 asi->insn_handler = handler;
310 return INSN_GOOD;
311 }
312
313 /* Fallback to slower simulation... */
314 if (reglist & 0x8000)
315 handler = is_ldm ? simulate_ldm1_pc : simulate_stm1_pc;
316 else
317 handler = simulate_ldm1stm1;
318 asi->insn_handler = handler;
319 return INSN_GOOD_NO_SLOT;
320}
321
322
323/*
324 * Prepare an instruction slot to receive an instruction for emulating.
325 * This is done by placing a subroutine return after the location where the
326 * instruction will be placed. We also modify ARM instructions to be
327 * unconditional as the condition code will already be checked before any
328 * emulation handler is called.
329 */
330static kprobe_opcode_t __kprobes
331prepare_emulated_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi,
332 bool thumb)
333{
334#ifdef CONFIG_THUMB2_KERNEL
335 if (thumb) {
336 u16 *thumb_insn = (u16 *)asi->insn;
337 thumb_insn[1] = 0x4770; /* Thumb bx lr */
338 thumb_insn[2] = 0x4770; /* Thumb bx lr */
339 return insn;
340 }
341 asi->insn[1] = 0xe12fff1e; /* ARM bx lr */
342#else
343 asi->insn[1] = 0xe1a0f00e; /* mov pc, lr */
344#endif
345 /* Make an ARM instruction unconditional */
346 if (insn < 0xe0000000)
347 insn = (insn | 0xe0000000) & ~0x10000000;
348 return insn;
349}
350
351/*
352 * Write a (probably modified) instruction into the slot previously prepared by
353 * prepare_emulated_insn
354 */
355static void __kprobes
356set_emulated_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi,
357 bool thumb)
358{
359#ifdef CONFIG_THUMB2_KERNEL
360 if (thumb) {
361 u16 *ip = (u16 *)asi->insn;
362 if (is_wide_instruction(insn))
363 *ip++ = insn >> 16;
364 *ip++ = insn;
365 return;
366 }
367#endif
368 asi->insn[0] = insn;
369}
370
371/*
372 * When we modify the register numbers encoded in an instruction to be emulated,
373 * the new values come from this define. For ARM and 32-bit Thumb instructions
374 * this gives...
375 *
376 * bit position 16 12 8 4 0
377 * ---------------+---+---+---+---+---+
378 * register r2 r0 r1 -- r3
379 */
380#define INSN_NEW_BITS 0x00020103
381
382/* Each nibble has same value as that at INSN_NEW_BITS bit 16 */
383#define INSN_SAMEAS16_BITS 0x22222222
384
385/*
386 * Validate and modify each of the registers encoded in an instruction.
387 *
388 * Each nibble in regs contains a value from enum decode_reg_type. For each
389 * non-zero value, the corresponding nibble in pinsn is validated and modified
390 * according to the type.
391 */
392static bool __kprobes decode_regs(kprobe_opcode_t* pinsn, u32 regs)
393{
394 kprobe_opcode_t insn = *pinsn;
395 kprobe_opcode_t mask = 0xf; /* Start at least significant nibble */
396
397 for (; regs != 0; regs >>= 4, mask <<= 4) {
398
399 kprobe_opcode_t new_bits = INSN_NEW_BITS;
400
401 switch (regs & 0xf) {
402
403 case REG_TYPE_NONE:
404 /* Nibble not a register, skip to next */
405 continue;
406
407 case REG_TYPE_ANY:
408 /* Any register is allowed */
409 break;
410
411 case REG_TYPE_SAMEAS16:
412 /* Replace register with same as at bit position 16 */
413 new_bits = INSN_SAMEAS16_BITS;
414 break;
415
416 case REG_TYPE_SP:
417 /* Only allow SP (R13) */
418 if ((insn ^ 0xdddddddd) & mask)
419 goto reject;
420 break;
421
422 case REG_TYPE_PC:
423 /* Only allow PC (R15) */
424 if ((insn ^ 0xffffffff) & mask)
425 goto reject;
426 break;
427
428 case REG_TYPE_NOSP:
429 /* Reject SP (R13) */
430 if (((insn ^ 0xdddddddd) & mask) == 0)
431 goto reject;
432 break;
433
434 case REG_TYPE_NOSPPC:
435 case REG_TYPE_NOSPPCX:
436 /* Reject SP and PC (R13 and R15) */
437 if (((insn ^ 0xdddddddd) & 0xdddddddd & mask) == 0)
438 goto reject;
439 break;
440
441 case REG_TYPE_NOPCWB:
442 if (!is_writeback(insn))
443 break; /* No writeback, so any register is OK */
444 /* fall through... */
445 case REG_TYPE_NOPC:
446 case REG_TYPE_NOPCX:
447 /* Reject PC (R15) */
448 if (((insn ^ 0xffffffff) & mask) == 0)
449 goto reject;
450 break;
451 }
452
453 /* Replace value of nibble with new register number... */
454 insn &= ~mask;
455 insn |= new_bits & mask;
456 }
457
458 *pinsn = insn;
459 return true;
460
461reject:
462 return false;
463}
464
465static const int decode_struct_sizes[NUM_DECODE_TYPES] = {
466 [DECODE_TYPE_TABLE] = sizeof(struct decode_table),
467 [DECODE_TYPE_CUSTOM] = sizeof(struct decode_custom),
468 [DECODE_TYPE_SIMULATE] = sizeof(struct decode_simulate),
469 [DECODE_TYPE_EMULATE] = sizeof(struct decode_emulate),
470 [DECODE_TYPE_OR] = sizeof(struct decode_or),
471 [DECODE_TYPE_REJECT] = sizeof(struct decode_reject)
472};
473
474/*
475 * kprobe_decode_insn operates on data tables in order to decode an ARM
476 * architecture instruction onto which a kprobe has been placed.
477 *
478 * These instruction decoding tables are a concatenation of entries each
479 * of which consist of one of the following structs:
480 *
481 * decode_table
482 * decode_custom
483 * decode_simulate
484 * decode_emulate
485 * decode_or
486 * decode_reject
487 *
488 * Each of these starts with a struct decode_header which has the following
489 * fields:
490 *
491 * type_regs
492 * mask
493 * value
494 *
495 * The least significant DECODE_TYPE_BITS of type_regs contains a value
496 * from enum decode_type, this indicates which of the decode_* structs
497 * the entry contains. The value DECODE_TYPE_END indicates the end of the
498 * table.
499 *
500 * When the table is parsed, each entry is checked in turn to see if it
501 * matches the instruction to be decoded using the test:
502 *
503 * (insn & mask) == value
504 *
505 * If no match is found before the end of the table is reached then decoding
506 * fails with INSN_REJECTED.
507 *
508 * When a match is found, decode_regs() is called to validate and modify each
509 * of the registers encoded in the instruction; the data it uses to do this
510 * is (type_regs >> DECODE_TYPE_BITS). A validation failure will cause decoding
511 * to fail with INSN_REJECTED.
512 *
513 * Once the instruction has passed the above tests, further processing
514 * depends on the type of the table entry's decode struct.
515 *
516 */
517int __kprobes
518kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi,
519 const union decode_item *table, bool thumb)
520{
521 const struct decode_header *h = (struct decode_header *)table;
522 const struct decode_header *next;
523 bool matched = false;
524
525 insn = prepare_emulated_insn(insn, asi, thumb);
526
527 for (;; h = next) {
528 enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK;
529 u32 regs = h->type_regs.bits >> DECODE_TYPE_BITS;
530
531 if (type == DECODE_TYPE_END)
532 return INSN_REJECTED;
533
534 next = (struct decode_header *)
535 ((uintptr_t)h + decode_struct_sizes[type]);
536
537 if (!matched && (insn & h->mask.bits) != h->value.bits)
538 continue;
539
540 if (!decode_regs(&insn, regs))
541 return INSN_REJECTED;
542
543 switch (type) {
544
545 case DECODE_TYPE_TABLE: {
546 struct decode_table *d = (struct decode_table *)h;
547 next = (struct decode_header *)d->table.table;
548 break;
549 }
550
551 case DECODE_TYPE_CUSTOM: {
552 struct decode_custom *d = (struct decode_custom *)h;
553 return (*d->decoder.decoder)(insn, asi);
554 }
555
556 case DECODE_TYPE_SIMULATE: {
557 struct decode_simulate *d = (struct decode_simulate *)h;
558 asi->insn_handler = d->handler.handler;
559 return INSN_GOOD_NO_SLOT;
560 }
561
562 case DECODE_TYPE_EMULATE: {
563 struct decode_emulate *d = (struct decode_emulate *)h;
564 asi->insn_handler = d->handler.handler;
565 set_emulated_insn(insn, asi, thumb);
566 return INSN_GOOD;
567 }
568
569 case DECODE_TYPE_OR:
570 matched = true;
571 break;
572
573 case DECODE_TYPE_REJECT:
574 default:
575 return INSN_REJECTED;
576 }
577 }
578 }