xref: /openbmc/linux/arch/sh/kernel/hw_breakpoint.c (revision 3a83e4e6) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * arch/sh/kernel/hw_breakpoint.c
4  *
5  * Unified kernel/user-space hardware breakpoint facility for the on-chip UBC.
6  *
7  * Copyright (C) 2009 - 2010  Paul Mundt
8  */
9 #include <linux/init.h>
10 #include <linux/perf_event.h>
11 #include <linux/sched/signal.h>
12 #include <linux/hw_breakpoint.h>
13 #include <linux/percpu.h>
14 #include <linux/kallsyms.h>
15 #include <linux/notifier.h>
16 #include <linux/kprobes.h>
17 #include <linux/kdebug.h>
18 #include <linux/io.h>
19 #include <linux/clk.h>
20 #include <asm/hw_breakpoint.h>
21 #include <asm/mmu_context.h>
22 #include <asm/ptrace.h>
23 #include <asm/traps.h>
24 
25 /*
26  * Stores the breakpoints currently in use on each breakpoint address
27  * register for each cpus
28  */
29 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
30 
31 /*
32  * A dummy placeholder for early accesses until the CPUs get a chance to
33  * register their UBCs later in the boot process.
34  */
35 static struct sh_ubc ubc_dummy = { .num_events = 0 };
36 
37 static struct sh_ubc *sh_ubc __read_mostly = &ubc_dummy;
38 
39 /*
40  * Install a perf counter breakpoint.
41  *
42  * We seek a free UBC channel and use it for this breakpoint.
43  *
44  * Atomic: we hold the counter->ctx->lock and we only handle variables
45  * and registers local to this cpu.
46  */
47 int arch_install_hw_breakpoint(struct perf_event *bp)
48 {
49 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
50 	int i;
51 
52 	for (i = 0; i < sh_ubc->num_events; i++) {
53 		struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
54 
55 		if (!*slot) {
56 			*slot = bp;
57 			break;
58 		}
59 	}
60 
61 	if (WARN_ONCE(i == sh_ubc->num_events, "Can't find any breakpoint slot"))
62 		return -EBUSY;
63 
64 	clk_enable(sh_ubc->clk);
65 	sh_ubc->enable(info, i);
66 
67 	return 0;
68 }
69 
70 /*
71  * Uninstall the breakpoint contained in the given counter.
72  *
73  * First we search the debug address register it uses and then we disable
74  * it.
75  *
76  * Atomic: we hold the counter->ctx->lock and we only handle variables
77  * and registers local to this cpu.
78  */
79 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
80 {
81 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
82 	int i;
83 
84 	for (i = 0; i < sh_ubc->num_events; i++) {
85 		struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
86 
87 		if (*slot == bp) {
88 			*slot = NULL;
89 			break;
90 		}
91 	}
92 
93 	if (WARN_ONCE(i == sh_ubc->num_events, "Can't find any breakpoint slot"))
94 		return;
95 
96 	sh_ubc->disable(info, i);
97 	clk_disable(sh_ubc->clk);
98 }
99 
100 static int get_hbp_len(u16 hbp_len)
101 {
102 	unsigned int len_in_bytes = 0;
103 
104 	switch (hbp_len) {
105 	case SH_BREAKPOINT_LEN_1:
106 		len_in_bytes = 1;
107 		break;
108 	case SH_BREAKPOINT_LEN_2:
109 		len_in_bytes = 2;
110 		break;
111 	case SH_BREAKPOINT_LEN_4:
112 		len_in_bytes = 4;
113 		break;
114 	case SH_BREAKPOINT_LEN_8:
115 		len_in_bytes = 8;
116 		break;
117 	}
118 	return len_in_bytes;
119 }
120 
121 /*
122  * Check for virtual address in kernel space.
123  */
124 int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
125 {
126 	unsigned int len;
127 	unsigned long va;
128 
129 	va = hw->address;
130 	len = get_hbp_len(hw->len);
131 
132 	return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
133 }
134 
135 int arch_bp_generic_fields(int sh_len, int sh_type,
136 			   int *gen_len, int *gen_type)
137 {
138 	/* Len */
139 	switch (sh_len) {
140 	case SH_BREAKPOINT_LEN_1:
141 		*gen_len = HW_BREAKPOINT_LEN_1;
142 		break;
143 	case SH_BREAKPOINT_LEN_2:
144 		*gen_len = HW_BREAKPOINT_LEN_2;
145 		break;
146 	case SH_BREAKPOINT_LEN_4:
147 		*gen_len = HW_BREAKPOINT_LEN_4;
148 		break;
149 	case SH_BREAKPOINT_LEN_8:
150 		*gen_len = HW_BREAKPOINT_LEN_8;
151 		break;
152 	default:
153 		return -EINVAL;
154 	}
155 
156 	/* Type */
157 	switch (sh_type) {
158 	case SH_BREAKPOINT_READ:
159 		*gen_type = HW_BREAKPOINT_R;
160 		break;
161 	case SH_BREAKPOINT_WRITE:
162 		*gen_type = HW_BREAKPOINT_W;
163 		break;
164 	case SH_BREAKPOINT_RW:
165 		*gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
166 		break;
167 	default:
168 		return -EINVAL;
169 	}
170 
171 	return 0;
172 }
173 
174 static int arch_build_bp_info(struct perf_event *bp,
175 			      const struct perf_event_attr *attr,
176 			      struct arch_hw_breakpoint *hw)
177 {
178 	hw->address = attr->bp_addr;
179 
180 	/* Len */
181 	switch (attr->bp_len) {
182 	case HW_BREAKPOINT_LEN_1:
183 		hw->len = SH_BREAKPOINT_LEN_1;
184 		break;
185 	case HW_BREAKPOINT_LEN_2:
186 		hw->len = SH_BREAKPOINT_LEN_2;
187 		break;
188 	case HW_BREAKPOINT_LEN_4:
189 		hw->len = SH_BREAKPOINT_LEN_4;
190 		break;
191 	case HW_BREAKPOINT_LEN_8:
192 		hw->len = SH_BREAKPOINT_LEN_8;
193 		break;
194 	default:
195 		return -EINVAL;
196 	}
197 
198 	/* Type */
199 	switch (attr->bp_type) {
200 	case HW_BREAKPOINT_R:
201 		hw->type = SH_BREAKPOINT_READ;
202 		break;
203 	case HW_BREAKPOINT_W:
204 		hw->type = SH_BREAKPOINT_WRITE;
205 		break;
206 	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
207 		hw->type = SH_BREAKPOINT_RW;
208 		break;
209 	default:
210 		return -EINVAL;
211 	}
212 
213 	return 0;
214 }
215 
216 /*
217  * Validate the arch-specific HW Breakpoint register settings
218  */
219 int hw_breakpoint_arch_parse(struct perf_event *bp,
220 			     const struct perf_event_attr *attr,
221 			     struct arch_hw_breakpoint *hw)
222 {
223 	unsigned int align;
224 	int ret;
225 
226 	ret = arch_build_bp_info(bp, attr, hw);
227 	if (ret)
228 		return ret;
229 
230 	ret = -EINVAL;
231 
232 	switch (hw->len) {
233 	case SH_BREAKPOINT_LEN_1:
234 		align = 0;
235 		break;
236 	case SH_BREAKPOINT_LEN_2:
237 		align = 1;
238 		break;
239 	case SH_BREAKPOINT_LEN_4:
240 		align = 3;
241 		break;
242 	case SH_BREAKPOINT_LEN_8:
243 		align = 7;
244 		break;
245 	default:
246 		return ret;
247 	}
248 
249 	/*
250 	 * Check that the low-order bits of the address are appropriate
251 	 * for the alignment implied by len.
252 	 */
253 	if (hw->address & align)
254 		return -EINVAL;
255 
256 	return 0;
257 }
258 
259 /*
260  * Release the user breakpoints used by ptrace
261  */
262 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
263 {
264 	int i;
265 	struct thread_struct *t = &tsk->thread;
266 
267 	for (i = 0; i < sh_ubc->num_events; i++) {
268 		unregister_hw_breakpoint(t->ptrace_bps[i]);
269 		t->ptrace_bps[i] = NULL;
270 	}
271 }
272 
273 static int __kprobes hw_breakpoint_handler(struct die_args *args)
274 {
275 	int cpu, i, rc = NOTIFY_STOP;
276 	struct perf_event *bp;
277 	unsigned int cmf, resume_mask;
278 
279 	/*
280 	 * Do an early return if none of the channels triggered.
281 	 */
282 	cmf = sh_ubc->triggered_mask();
283 	if (unlikely(!cmf))
284 		return NOTIFY_DONE;
285 
286 	/*
287 	 * By default, resume all of the active channels.
288 	 */
289 	resume_mask = sh_ubc->active_mask();
290 
291 	/*
292 	 * Disable breakpoints during exception handling.
293 	 */
294 	sh_ubc->disable_all();
295 
296 	cpu = get_cpu();
297 	for (i = 0; i < sh_ubc->num_events; i++) {
298 		unsigned long event_mask = (1 << i);
299 
300 		if (likely(!(cmf & event_mask)))
301 			continue;
302 
303 		/*
304 		 * The counter may be concurrently released but that can only
305 		 * occur from a call_rcu() path. We can then safely fetch
306 		 * the breakpoint, use its callback, touch its counter
307 		 * while we are in an rcu_read_lock() path.
308 		 */
309 		rcu_read_lock();
310 
311 		bp = per_cpu(bp_per_reg[i], cpu);
312 		if (bp)
313 			rc = NOTIFY_DONE;
314 
315 		/*
316 		 * Reset the condition match flag to denote completion of
317 		 * exception handling.
318 		 */
319 		sh_ubc->clear_triggered_mask(event_mask);
320 
321 		/*
322 		 * bp can be NULL due to concurrent perf counter
323 		 * removing.
324 		 */
325 		if (!bp) {
326 			rcu_read_unlock();
327 			break;
328 		}
329 
330 		/*
331 		 * Don't restore the channel if the breakpoint is from
332 		 * ptrace, as it always operates in one-shot mode.
333 		 */
334 		if (bp->overflow_handler == ptrace_triggered)
335 			resume_mask &= ~(1 << i);
336 
337 		perf_bp_event(bp, args->regs);
338 
339 		/* Deliver the signal to userspace */
340 		if (!arch_check_bp_in_kernelspace(&bp->hw.info)) {
341 			force_sig_fault(SIGTRAP, TRAP_HWBKPT,
342 					(void __user *)NULL);
343 		}
344 
345 		rcu_read_unlock();
346 	}
347 
348 	if (cmf == 0)
349 		rc = NOTIFY_DONE;
350 
351 	sh_ubc->enable_all(resume_mask);
352 
353 	put_cpu();
354 
355 	return rc;
356 }
357 
358 BUILD_TRAP_HANDLER(breakpoint)
359 {
360 	unsigned long ex = lookup_exception_vector();
361 	TRAP_HANDLER_DECL;
362 
363 	notify_die(DIE_BREAKPOINT, "breakpoint", regs, 0, ex, SIGTRAP);
364 }
365 
366 /*
367  * Handle debug exception notifications.
368  */
369 int __kprobes hw_breakpoint_exceptions_notify(struct notifier_block *unused,
370 				    unsigned long val, void *data)
371 {
372 	struct die_args *args = data;
373 
374 	if (val != DIE_BREAKPOINT)
375 		return NOTIFY_DONE;
376 
377 	/*
378 	 * If the breakpoint hasn't been triggered by the UBC, it's
379 	 * probably from a debugger, so don't do anything more here.
380 	 *
381 	 * This also permits the UBC interface clock to remain off for
382 	 * non-UBC breakpoints, as we don't need to check the triggered
383 	 * or active channel masks.
384 	 */
385 	if (args->trapnr != sh_ubc->trap_nr)
386 		return NOTIFY_DONE;
387 
388 	return hw_breakpoint_handler(data);
389 }
390 
391 void hw_breakpoint_pmu_read(struct perf_event *bp)
392 {
393 	/* TODO */
394 }
395 
396 int register_sh_ubc(struct sh_ubc *ubc)
397 {
398 	/* Bail if it's already assigned */
399 	if (sh_ubc != &ubc_dummy)
400 		return -EBUSY;
401 	sh_ubc = ubc;
402 
403 	pr_info("HW Breakpoints: %s UBC support registered\n", ubc->name);
404 
405 	WARN_ON(ubc->num_events > HBP_NUM);
406 
407 	return 0;
408 }
409