1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/kdebug.h>
3 #include <linux/kprobes.h>
4 #include <linux/preempt.h>
5 #include <asm/break.h>
6 
7 #define KPROBE_BP_INSN		__emit_break(BRK_KPROBE_BP)
8 #define KPROBE_SSTEPBP_INSN	__emit_break(BRK_KPROBE_SSTEPBP)
9 
10 DEFINE_PER_CPU(struct kprobe *, current_kprobe);
11 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
12 
arch_prepare_ss_slot(struct kprobe * p)13 static void arch_prepare_ss_slot(struct kprobe *p)
14 {
15 	p->ainsn.insn[0] = *p->addr;
16 	p->ainsn.insn[1] = KPROBE_SSTEPBP_INSN;
17 	p->ainsn.restore = (unsigned long)p->addr + LOONGARCH_INSN_SIZE;
18 }
19 NOKPROBE_SYMBOL(arch_prepare_ss_slot);
20 
arch_prepare_simulate(struct kprobe * p)21 static void arch_prepare_simulate(struct kprobe *p)
22 {
23 	p->ainsn.restore = 0;
24 }
25 NOKPROBE_SYMBOL(arch_prepare_simulate);
26 
arch_prepare_kprobe(struct kprobe * p)27 int arch_prepare_kprobe(struct kprobe *p)
28 {
29 	union loongarch_instruction insn;
30 
31 	if ((unsigned long)p->addr & 0x3)
32 		return -EILSEQ;
33 
34 	/* copy instruction */
35 	p->opcode = *p->addr;
36 	insn.word = p->opcode;
37 
38 	/* decode instruction */
39 	if (insns_not_supported(insn))
40 		return -EINVAL;
41 
42 	if (insns_need_simulation(insn)) {
43 		p->ainsn.insn = NULL;
44 	} else {
45 		p->ainsn.insn = get_insn_slot();
46 		if (!p->ainsn.insn)
47 			return -ENOMEM;
48 	}
49 
50 	/* prepare the instruction */
51 	if (p->ainsn.insn)
52 		arch_prepare_ss_slot(p);
53 	else
54 		arch_prepare_simulate(p);
55 
56 	return 0;
57 }
58 NOKPROBE_SYMBOL(arch_prepare_kprobe);
59 
60 /* Install breakpoint in text */
arch_arm_kprobe(struct kprobe * p)61 void arch_arm_kprobe(struct kprobe *p)
62 {
63 	*p->addr = KPROBE_BP_INSN;
64 	flush_insn_slot(p);
65 }
66 NOKPROBE_SYMBOL(arch_arm_kprobe);
67 
68 /* Remove breakpoint from text */
arch_disarm_kprobe(struct kprobe * p)69 void arch_disarm_kprobe(struct kprobe *p)
70 {
71 	*p->addr = p->opcode;
72 	flush_insn_slot(p);
73 }
74 NOKPROBE_SYMBOL(arch_disarm_kprobe);
75 
arch_remove_kprobe(struct kprobe * p)76 void arch_remove_kprobe(struct kprobe *p)
77 {
78 	if (p->ainsn.insn) {
79 		free_insn_slot(p->ainsn.insn, 0);
80 		p->ainsn.insn = NULL;
81 	}
82 }
83 NOKPROBE_SYMBOL(arch_remove_kprobe);
84 
save_previous_kprobe(struct kprobe_ctlblk * kcb)85 static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
86 {
87 	kcb->prev_kprobe.kp = kprobe_running();
88 	kcb->prev_kprobe.status = kcb->kprobe_status;
89 }
90 NOKPROBE_SYMBOL(save_previous_kprobe);
91 
restore_previous_kprobe(struct kprobe_ctlblk * kcb)92 static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
93 {
94 	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
95 	kcb->kprobe_status = kcb->prev_kprobe.status;
96 }
97 NOKPROBE_SYMBOL(restore_previous_kprobe);
98 
set_current_kprobe(struct kprobe * p)99 static void set_current_kprobe(struct kprobe *p)
100 {
101 	__this_cpu_write(current_kprobe, p);
102 }
103 NOKPROBE_SYMBOL(set_current_kprobe);
104 
105 /*
106  * Interrupts need to be disabled before single-step mode is set,
107  * and not reenabled until after single-step mode ends.
108  * Without disabling interrupt on local CPU, there is a chance of
109  * interrupt occurrence in the period of exception return and start
110  * of out-of-line single-step, that result in wrongly single stepping
111  * into the interrupt handler.
112  */
save_local_irqflag(struct kprobe_ctlblk * kcb,struct pt_regs * regs)113 static void save_local_irqflag(struct kprobe_ctlblk *kcb,
114 			       struct pt_regs *regs)
115 {
116 	kcb->saved_status = regs->csr_prmd;
117 	regs->csr_prmd &= ~CSR_PRMD_PIE;
118 }
119 NOKPROBE_SYMBOL(save_local_irqflag);
120 
restore_local_irqflag(struct kprobe_ctlblk * kcb,struct pt_regs * regs)121 static void restore_local_irqflag(struct kprobe_ctlblk *kcb,
122 				  struct pt_regs *regs)
123 {
124 	regs->csr_prmd = kcb->saved_status;
125 }
126 NOKPROBE_SYMBOL(restore_local_irqflag);
127 
post_kprobe_handler(struct kprobe * cur,struct kprobe_ctlblk * kcb,struct pt_regs * regs)128 static void post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb,
129 				struct pt_regs *regs)
130 {
131 	/* return addr restore if non-branching insn */
132 	if (cur->ainsn.restore != 0)
133 		instruction_pointer_set(regs, cur->ainsn.restore);
134 
135 	/* restore back original saved kprobe variables and continue */
136 	if (kcb->kprobe_status == KPROBE_REENTER) {
137 		restore_previous_kprobe(kcb);
138 		preempt_enable_no_resched();
139 		return;
140 	}
141 
142 	/*
143 	 * update the kcb status even if the cur->post_handler is
144 	 * not set because reset_curent_kprobe() doesn't update kcb.
145 	 */
146 	kcb->kprobe_status = KPROBE_HIT_SSDONE;
147 	if (cur->post_handler)
148 		cur->post_handler(cur, regs, 0);
149 
150 	reset_current_kprobe();
151 	preempt_enable_no_resched();
152 }
153 NOKPROBE_SYMBOL(post_kprobe_handler);
154 
setup_singlestep(struct kprobe * p,struct pt_regs * regs,struct kprobe_ctlblk * kcb,int reenter)155 static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
156 			     struct kprobe_ctlblk *kcb, int reenter)
157 {
158 	union loongarch_instruction insn;
159 
160 	if (reenter) {
161 		save_previous_kprobe(kcb);
162 		set_current_kprobe(p);
163 		kcb->kprobe_status = KPROBE_REENTER;
164 	} else {
165 		kcb->kprobe_status = KPROBE_HIT_SS;
166 	}
167 
168 	if (p->ainsn.insn) {
169 		/* IRQs and single stepping do not mix well */
170 		save_local_irqflag(kcb, regs);
171 		/* set ip register to prepare for single stepping */
172 		regs->csr_era = (unsigned long)p->ainsn.insn;
173 	} else {
174 		/* simulate single steping */
175 		insn.word = p->opcode;
176 		arch_simulate_insn(insn, regs);
177 		/* now go for post processing */
178 		post_kprobe_handler(p, kcb, regs);
179 	}
180 }
181 NOKPROBE_SYMBOL(setup_singlestep);
182 
reenter_kprobe(struct kprobe * p,struct pt_regs * regs,struct kprobe_ctlblk * kcb)183 static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
184 			   struct kprobe_ctlblk *kcb)
185 {
186 	switch (kcb->kprobe_status) {
187 	case KPROBE_HIT_SS:
188 	case KPROBE_HIT_SSDONE:
189 	case KPROBE_HIT_ACTIVE:
190 		kprobes_inc_nmissed_count(p);
191 		setup_singlestep(p, regs, kcb, 1);
192 		break;
193 	case KPROBE_REENTER:
194 		pr_warn("Failed to recover from reentered kprobes.\n");
195 		dump_kprobe(p);
196 		WARN_ON_ONCE(1);
197 		break;
198 	default:
199 		WARN_ON(1);
200 		return false;
201 	}
202 
203 	return true;
204 }
205 NOKPROBE_SYMBOL(reenter_kprobe);
206 
kprobe_breakpoint_handler(struct pt_regs * regs)207 bool kprobe_breakpoint_handler(struct pt_regs *regs)
208 {
209 	struct kprobe_ctlblk *kcb;
210 	struct kprobe *p, *cur_kprobe;
211 	kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->csr_era;
212 
213 	/*
214 	 * We don't want to be preempted for the entire
215 	 * duration of kprobe processing.
216 	 */
217 	preempt_disable();
218 	kcb = get_kprobe_ctlblk();
219 	cur_kprobe = kprobe_running();
220 
221 	p = get_kprobe(addr);
222 	if (p) {
223 		if (cur_kprobe) {
224 			if (reenter_kprobe(p, regs, kcb))
225 				return true;
226 		} else {
227 			/* Probe hit */
228 			set_current_kprobe(p);
229 			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
230 
231 			/*
232 			 * If we have no pre-handler or it returned 0, we
233 			 * continue with normal processing.  If we have a
234 			 * pre-handler and it returned non-zero, it will
235 			 * modify the execution path and no need to single
236 			 * stepping. Let's just reset current kprobe and exit.
237 			 *
238 			 * pre_handler can hit a breakpoint and can step thru
239 			 * before return.
240 			 */
241 			if (!p->pre_handler || !p->pre_handler(p, regs)) {
242 				setup_singlestep(p, regs, kcb, 0);
243 			} else {
244 				reset_current_kprobe();
245 				preempt_enable_no_resched();
246 			}
247 			return true;
248 		}
249 	}
250 
251 	if (*addr != KPROBE_BP_INSN) {
252 		/*
253 		 * The breakpoint instruction was removed right
254 		 * after we hit it.  Another cpu has removed
255 		 * either a probepoint or a debugger breakpoint
256 		 * at this address.  In either case, no further
257 		 * handling of this interrupt is appropriate.
258 		 * Return back to original instruction, and continue.
259 		 */
260 		regs->csr_era = (unsigned long)addr;
261 		preempt_enable_no_resched();
262 		return true;
263 	}
264 
265 	preempt_enable_no_resched();
266 	return false;
267 }
268 NOKPROBE_SYMBOL(kprobe_breakpoint_handler);
269 
kprobe_singlestep_handler(struct pt_regs * regs)270 bool kprobe_singlestep_handler(struct pt_regs *regs)
271 {
272 	struct kprobe *cur = kprobe_running();
273 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
274 	unsigned long addr = instruction_pointer(regs);
275 
276 	if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
277 	    ((unsigned long)&cur->ainsn.insn[1] == addr)) {
278 		restore_local_irqflag(kcb, regs);
279 		post_kprobe_handler(cur, kcb, regs);
280 		return true;
281 	}
282 
283 	preempt_enable_no_resched();
284 	return false;
285 }
286 NOKPROBE_SYMBOL(kprobe_singlestep_handler);
287 
kprobe_fault_handler(struct pt_regs * regs,int trapnr)288 bool kprobe_fault_handler(struct pt_regs *regs, int trapnr)
289 {
290 	struct kprobe *cur = kprobe_running();
291 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
292 
293 	switch (kcb->kprobe_status) {
294 	case KPROBE_HIT_SS:
295 	case KPROBE_REENTER:
296 		/*
297 		 * We are here because the instruction being single
298 		 * stepped caused a page fault. We reset the current
299 		 * kprobe and the ip points back to the probe address
300 		 * and allow the page fault handler to continue as a
301 		 * normal page fault.
302 		 */
303 		regs->csr_era = (unsigned long)cur->addr;
304 		WARN_ON_ONCE(!instruction_pointer(regs));
305 
306 		if (kcb->kprobe_status == KPROBE_REENTER) {
307 			restore_previous_kprobe(kcb);
308 		} else {
309 			restore_local_irqflag(kcb, regs);
310 			reset_current_kprobe();
311 		}
312 		preempt_enable_no_resched();
313 		break;
314 	}
315 	return false;
316 }
317 NOKPROBE_SYMBOL(kprobe_fault_handler);
318 
319 /*
320  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
321  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
322  */
arch_populate_kprobe_blacklist(void)323 int __init arch_populate_kprobe_blacklist(void)
324 {
325 	return kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
326 					 (unsigned long)__irqentry_text_end);
327 }
328 
arch_init_kprobes(void)329 int __init arch_init_kprobes(void)
330 {
331 	return 0;
332 }
333 
arch_trampoline_kprobe(struct kprobe * p)334 int arch_trampoline_kprobe(struct kprobe *p)
335 {
336 	return 0;
337 }
338 NOKPROBE_SYMBOL(arch_trampoline_kprobe);
339