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
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