1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Kernel Probes Jump Optimization (Optprobes)
4 *
5 * Copyright (C) IBM Corporation, 2002, 2004
6 * Copyright (C) Hitachi Ltd., 2012
7 * Copyright (C) Huawei Inc., 2014
8 */
9
10 #include <linux/kprobes.h>
11 #include <linux/jump_label.h>
12 #include <asm/kprobes.h>
13 #include <asm/cacheflush.h>
14 /* for arm_gen_branch */
15 #include <asm/insn.h>
16 /* for patch_text */
17 #include <asm/patch.h>
18
19 #include "core.h"
20
21 /*
22 * See register_usage_flags. If the probed instruction doesn't use PC,
23 * we can copy it into template and have it executed directly without
24 * simulation or emulation.
25 */
26 #define ARM_REG_PC 15
27 #define can_kprobe_direct_exec(m) (!test_bit(ARM_REG_PC, &(m)))
28
29 /*
30 * NOTE: the first sub and add instruction will be modified according
31 * to the stack cost of the instruction.
32 */
33 asm (
34 ".global optprobe_template_entry\n"
35 "optprobe_template_entry:\n"
36 ".global optprobe_template_sub_sp\n"
37 "optprobe_template_sub_sp:"
38 " sub sp, sp, #0xff\n"
39 " stmia sp, {r0 - r14} \n"
40 ".global optprobe_template_add_sp\n"
41 "optprobe_template_add_sp:"
42 " add r3, sp, #0xff\n"
43 " str r3, [sp, #52]\n"
44 " mrs r4, cpsr\n"
45 " str r4, [sp, #64]\n"
46 " mov r1, sp\n"
47 " ldr r0, 1f\n"
48 " ldr r2, 2f\n"
49 /*
50 * AEABI requires an 8-bytes alignment stack. If
51 * SP % 8 != 0 (SP % 4 == 0 should be ensured),
52 * alloc more bytes here.
53 */
54 " and r4, sp, #4\n"
55 " sub sp, sp, r4\n"
56 #if __LINUX_ARM_ARCH__ >= 5
57 " blx r2\n"
58 #else
59 " mov lr, pc\n"
60 " mov pc, r2\n"
61 #endif
62 " add sp, sp, r4\n"
63 " ldr r1, [sp, #64]\n"
64 " tst r1, #"__stringify(PSR_T_BIT)"\n"
65 " ldrne r2, [sp, #60]\n"
66 " orrne r2, #1\n"
67 " strne r2, [sp, #60] @ set bit0 of PC for thumb\n"
68 " msr cpsr_cxsf, r1\n"
69 ".global optprobe_template_restore_begin\n"
70 "optprobe_template_restore_begin:\n"
71 " ldmia sp, {r0 - r15}\n"
72 ".global optprobe_template_restore_orig_insn\n"
73 "optprobe_template_restore_orig_insn:\n"
74 " nop\n"
75 ".global optprobe_template_restore_end\n"
76 "optprobe_template_restore_end:\n"
77 " nop\n"
78 ".global optprobe_template_val\n"
79 "optprobe_template_val:\n"
80 "1: .long 0\n"
81 ".global optprobe_template_call\n"
82 "optprobe_template_call:\n"
83 "2: .long 0\n"
84 ".global optprobe_template_end\n"
85 "optprobe_template_end:\n");
86
87 #define TMPL_VAL_IDX \
88 ((unsigned long *)optprobe_template_val - (unsigned long *)optprobe_template_entry)
89 #define TMPL_CALL_IDX \
90 ((unsigned long *)optprobe_template_call - (unsigned long *)optprobe_template_entry)
91 #define TMPL_END_IDX \
92 ((unsigned long *)optprobe_template_end - (unsigned long *)optprobe_template_entry)
93 #define TMPL_ADD_SP \
94 ((unsigned long *)optprobe_template_add_sp - (unsigned long *)optprobe_template_entry)
95 #define TMPL_SUB_SP \
96 ((unsigned long *)optprobe_template_sub_sp - (unsigned long *)optprobe_template_entry)
97 #define TMPL_RESTORE_BEGIN \
98 ((unsigned long *)optprobe_template_restore_begin - (unsigned long *)optprobe_template_entry)
99 #define TMPL_RESTORE_ORIGN_INSN \
100 ((unsigned long *)optprobe_template_restore_orig_insn - (unsigned long *)optprobe_template_entry)
101 #define TMPL_RESTORE_END \
102 ((unsigned long *)optprobe_template_restore_end - (unsigned long *)optprobe_template_entry)
103
104 /*
105 * ARM can always optimize an instruction when using ARM ISA, except
106 * instructions like 'str r0, [sp, r1]' which store to stack and unable
107 * to determine stack space consumption statically.
108 */
arch_prepared_optinsn(struct arch_optimized_insn * optinsn)109 int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
110 {
111 return optinsn->insn != NULL;
112 }
113
114 /*
115 * In ARM ISA, kprobe opt always replace one instruction (4 bytes
116 * aligned and 4 bytes long). It is impossible to encounter another
117 * kprobe in the address range. So always return 0.
118 */
arch_check_optimized_kprobe(struct optimized_kprobe * op)119 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
120 {
121 return 0;
122 }
123
124 /* Caller must ensure addr & 3 == 0 */
can_optimize(struct kprobe * kp)125 static int can_optimize(struct kprobe *kp)
126 {
127 if (kp->ainsn.stack_space < 0)
128 return 0;
129 /*
130 * 255 is the biggest imm can be used in 'sub r0, r0, #<imm>'.
131 * Number larger than 255 needs special encoding.
132 */
133 if (kp->ainsn.stack_space > 255 - sizeof(struct pt_regs))
134 return 0;
135 return 1;
136 }
137
138 /* Free optimized instruction slot */
139 static void
__arch_remove_optimized_kprobe(struct optimized_kprobe * op,int dirty)140 __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
141 {
142 if (op->optinsn.insn) {
143 free_optinsn_slot(op->optinsn.insn, dirty);
144 op->optinsn.insn = NULL;
145 }
146 }
147
148 extern void kprobe_handler(struct pt_regs *regs);
149
150 static void
optimized_callback(struct optimized_kprobe * op,struct pt_regs * regs)151 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
152 {
153 unsigned long flags;
154 struct kprobe *p = &op->kp;
155 struct kprobe_ctlblk *kcb;
156
157 /* Save skipped registers */
158 regs->ARM_pc = (unsigned long)op->kp.addr;
159 regs->ARM_ORIG_r0 = ~0UL;
160
161 local_irq_save(flags);
162 kcb = get_kprobe_ctlblk();
163
164 if (kprobe_running()) {
165 kprobes_inc_nmissed_count(&op->kp);
166 } else {
167 __this_cpu_write(current_kprobe, &op->kp);
168 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
169 opt_pre_handler(&op->kp, regs);
170 __this_cpu_write(current_kprobe, NULL);
171 }
172
173 /*
174 * We singlestep the replaced instruction only when it can't be
175 * executed directly during restore.
176 */
177 if (!p->ainsn.kprobe_direct_exec)
178 op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
179
180 local_irq_restore(flags);
181 }
NOKPROBE_SYMBOL(optimized_callback)182 NOKPROBE_SYMBOL(optimized_callback)
183
184 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
185 {
186 kprobe_opcode_t *code;
187 unsigned long rel_chk;
188 unsigned long val;
189 unsigned long stack_protect = sizeof(struct pt_regs);
190
191 if (!can_optimize(orig))
192 return -EILSEQ;
193
194 code = get_optinsn_slot();
195 if (!code)
196 return -ENOMEM;
197
198 /*
199 * Verify if the address gap is in 32MiB range, because this uses
200 * a relative jump.
201 *
202 * kprobe opt use a 'b' instruction to branch to optinsn.insn.
203 * According to ARM manual, branch instruction is:
204 *
205 * 31 28 27 24 23 0
206 * +------+---+---+---+---+----------------+
207 * | cond | 1 | 0 | 1 | 0 | imm24 |
208 * +------+---+---+---+---+----------------+
209 *
210 * imm24 is a signed 24 bits integer. The real branch offset is computed
211 * by: imm32 = SignExtend(imm24:'00', 32);
212 *
213 * So the maximum forward branch should be:
214 * (0x007fffff << 2) = 0x01fffffc = 0x1fffffc
215 * The maximum backword branch should be:
216 * (0xff800000 << 2) = 0xfe000000 = -0x2000000
217 *
218 * We can simply check (rel & 0xfe000003):
219 * if rel is positive, (rel & 0xfe000000) shoule be 0
220 * if rel is negitive, (rel & 0xfe000000) should be 0xfe000000
221 * the last '3' is used for alignment checking.
222 */
223 rel_chk = (unsigned long)((long)code -
224 (long)orig->addr + 8) & 0xfe000003;
225
226 if ((rel_chk != 0) && (rel_chk != 0xfe000000)) {
227 /*
228 * Different from x86, we free code buf directly instead of
229 * calling __arch_remove_optimized_kprobe() because
230 * we have not fill any field in op.
231 */
232 free_optinsn_slot(code, 0);
233 return -ERANGE;
234 }
235
236 /* Copy arch-dep-instance from template. */
237 memcpy(code, (unsigned long *)optprobe_template_entry,
238 TMPL_END_IDX * sizeof(kprobe_opcode_t));
239
240 /* Adjust buffer according to instruction. */
241 BUG_ON(orig->ainsn.stack_space < 0);
242
243 stack_protect += orig->ainsn.stack_space;
244
245 /* Should have been filtered by can_optimize(). */
246 BUG_ON(stack_protect > 255);
247
248 /* Create a 'sub sp, sp, #<stack_protect>' */
249 code[TMPL_SUB_SP] = __opcode_to_mem_arm(0xe24dd000 | stack_protect);
250 /* Create a 'add r3, sp, #<stack_protect>' */
251 code[TMPL_ADD_SP] = __opcode_to_mem_arm(0xe28d3000 | stack_protect);
252
253 /* Set probe information */
254 val = (unsigned long)op;
255 code[TMPL_VAL_IDX] = val;
256
257 /* Set probe function call */
258 val = (unsigned long)optimized_callback;
259 code[TMPL_CALL_IDX] = val;
260
261 /* If possible, copy insn and have it executed during restore */
262 orig->ainsn.kprobe_direct_exec = false;
263 if (can_kprobe_direct_exec(orig->ainsn.register_usage_flags)) {
264 kprobe_opcode_t final_branch = arm_gen_branch(
265 (unsigned long)(&code[TMPL_RESTORE_END]),
266 (unsigned long)(op->kp.addr) + 4);
267 if (final_branch != 0) {
268 /*
269 * Replace original 'ldmia sp, {r0 - r15}' with
270 * 'ldmia {r0 - r14}', restore all registers except pc.
271 */
272 code[TMPL_RESTORE_BEGIN] = __opcode_to_mem_arm(0xe89d7fff);
273
274 /* The original probed instruction */
275 code[TMPL_RESTORE_ORIGN_INSN] = __opcode_to_mem_arm(orig->opcode);
276
277 /* Jump back to next instruction */
278 code[TMPL_RESTORE_END] = __opcode_to_mem_arm(final_branch);
279 orig->ainsn.kprobe_direct_exec = true;
280 }
281 }
282
283 flush_icache_range((unsigned long)code,
284 (unsigned long)(&code[TMPL_END_IDX]));
285
286 /* Set op->optinsn.insn means prepared. */
287 op->optinsn.insn = code;
288 return 0;
289 }
290
arch_optimize_kprobes(struct list_head * oplist)291 void __kprobes arch_optimize_kprobes(struct list_head *oplist)
292 {
293 struct optimized_kprobe *op, *tmp;
294
295 list_for_each_entry_safe(op, tmp, oplist, list) {
296 unsigned long insn;
297 WARN_ON(kprobe_disabled(&op->kp));
298
299 /*
300 * Backup instructions which will be replaced
301 * by jump address
302 */
303 memcpy(op->optinsn.copied_insn, op->kp.addr,
304 RELATIVEJUMP_SIZE);
305
306 insn = arm_gen_branch((unsigned long)op->kp.addr,
307 (unsigned long)op->optinsn.insn);
308 BUG_ON(insn == 0);
309
310 /*
311 * Make it a conditional branch if replaced insn
312 * is consitional
313 */
314 insn = (__mem_to_opcode_arm(
315 op->optinsn.copied_insn[0]) & 0xf0000000) |
316 (insn & 0x0fffffff);
317
318 /*
319 * Similar to __arch_disarm_kprobe, operations which
320 * removing breakpoints must be wrapped by stop_machine
321 * to avoid racing.
322 */
323 kprobes_remove_breakpoint(op->kp.addr, insn);
324
325 list_del_init(&op->list);
326 }
327 }
328
arch_unoptimize_kprobe(struct optimized_kprobe * op)329 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
330 {
331 arch_arm_kprobe(&op->kp);
332 }
333
334 /*
335 * Recover original instructions and breakpoints from relative jumps.
336 * Caller must call with locking kprobe_mutex.
337 */
arch_unoptimize_kprobes(struct list_head * oplist,struct list_head * done_list)338 void arch_unoptimize_kprobes(struct list_head *oplist,
339 struct list_head *done_list)
340 {
341 struct optimized_kprobe *op, *tmp;
342
343 list_for_each_entry_safe(op, tmp, oplist, list) {
344 arch_unoptimize_kprobe(op);
345 list_move(&op->list, done_list);
346 }
347 }
348
arch_within_optimized_kprobe(struct optimized_kprobe * op,unsigned long addr)349 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
350 unsigned long addr)
351 {
352 return ((unsigned long)op->kp.addr <= addr &&
353 (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
354 }
355
arch_remove_optimized_kprobe(struct optimized_kprobe * op)356 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
357 {
358 __arch_remove_optimized_kprobe(op, 1);
359 }
360