kprobes.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * arch/arm64/kernel/probes/kprobes.c
  4 *
  5 * Kprobes support for ARM64
  6 *
  7 * Copyright (C) 2013 Linaro Limited.
  8 * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
  9 */
 10
 11#define pr_fmt(fmt) "kprobes: " fmt
 12
 13#include <linux/execmem.h>
 14#include <linux/extable.h>
 15#include <linux/kasan.h>
 16#include <linux/kernel.h>
 17#include <linux/kprobes.h>
 18#include <linux/sched/debug.h>
 19#include <linux/set_memory.h>
 20#include <linux/slab.h>
 21#include <linux/stop_machine.h>
 22#include <linux/stringify.h>
 23#include <linux/uaccess.h>
 24#include <linux/vmalloc.h>
 25
 26#include <asm/cacheflush.h>
 27#include <asm/daifflags.h>
 28#include <asm/debug-monitors.h>
 29#include <asm/insn.h>
 30#include <asm/irq.h>
 31#include <asm/text-patching.h>
 32#include <asm/ptrace.h>
 33#include <asm/sections.h>
 34#include <asm/system_misc.h>
 35#include <asm/traps.h>
 36
 37#include "decode-insn.h"
 38
 39DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 40DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 41
 42static void __kprobes
 43post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
 44
 45void *alloc_insn_page(void)
 46{
 47	void *addr;
 48
 49	addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
 50	if (!addr)
 51		return NULL;
 52	if (set_memory_rox((unsigned long)addr, 1)) {
 53		execmem_free(addr);
 54		return NULL;
 55	}
 56	return addr;
 57}
 58
 59static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 60{
 61	kprobe_opcode_t *addr = p->ainsn.xol_insn;
 62
 63	/*
 64	 * Prepare insn slot, Mark Rutland points out it depends on a coupe of
 65	 * subtleties:
 66	 *
 67	 * - That the I-cache maintenance for these instructions is complete
 68	 *   *before* the kprobe BRK is written (and aarch64_insn_patch_text_nosync()
 69	 *   ensures this, but just omits causing a Context-Synchronization-Event
 70	 *   on all CPUS).
 71	 *
 72	 * - That the kprobe BRK results in an exception (and consequently a
 73	 *   Context-Synchronoization-Event), which ensures that the CPU will
 74	 *   fetch thesingle-step slot instructions *after* this, ensuring that
 75	 *   the new instructions are used
 76	 *
 77	 * It supposes to place ISB after patching to guarantee I-cache maintenance
 78	 * is observed on all CPUS, however, single-step slot is installed in
 79	 * the BRK exception handler, so it is unnecessary to generate
 80	 * Contex-Synchronization-Event via ISB again.
 81	 */
 82	aarch64_insn_patch_text_nosync(addr, le32_to_cpu(p->opcode));
 83	aarch64_insn_patch_text_nosync(addr + 1, BRK64_OPCODE_KPROBES_SS);
 84
 85	/*
 86	 * Needs restoring of return address after stepping xol.
 87	 */
 88	p->ainsn.xol_restore = (unsigned long) p->addr +
 89	  sizeof(kprobe_opcode_t);
 90}
 91
 92static void __kprobes arch_prepare_simulate(struct kprobe *p)
 93{
 94	/* This instructions is not executed xol. No need to adjust the PC */
 95	p->ainsn.xol_restore = 0;
 96}
 97
 98static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
 99{
100	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
101
102	if (p->ainsn.api.handler)
103		p->ainsn.api.handler(le32_to_cpu(p->opcode), (long)p->addr, regs);
104
105	/* single step simulated, now go for post processing */
106	post_kprobe_handler(p, kcb, regs);
107}
108
109int __kprobes arch_prepare_kprobe(struct kprobe *p)
110{
111	unsigned long probe_addr = (unsigned long)p->addr;
112
113	if (probe_addr & 0x3)
114		return -EINVAL;
115
116	/* copy instruction */
117	p->opcode = *p->addr;
118
119	if (search_exception_tables(probe_addr))
120		return -EINVAL;
121
122	/* decode instruction */
123	switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
124	case INSN_REJECTED:	/* insn not supported */
125		return -EINVAL;
126
127	case INSN_GOOD_NO_SLOT:	/* insn need simulation */
128		p->ainsn.xol_insn = NULL;
129		break;
130
131	case INSN_GOOD:	/* instruction uses slot */
132		p->ainsn.xol_insn = get_insn_slot();
133		if (!p->ainsn.xol_insn)
134			return -ENOMEM;
135		break;
136	}
137
138	/* prepare the instruction */
139	if (p->ainsn.xol_insn)
140		arch_prepare_ss_slot(p);
141	else
142		arch_prepare_simulate(p);
143
144	return 0;
145}
146
147/* arm kprobe: install breakpoint in text */
148void __kprobes arch_arm_kprobe(struct kprobe *p)
149{
150	void *addr = p->addr;
151	u32 insn = BRK64_OPCODE_KPROBES;
152
153	aarch64_insn_patch_text(&addr, &insn, 1);
154}
155
156/* disarm kprobe: remove breakpoint from text */
157void __kprobes arch_disarm_kprobe(struct kprobe *p)
158{
159	void *addr = p->addr;
160	u32 insn = le32_to_cpu(p->opcode);
161
162	aarch64_insn_patch_text(&addr, &insn, 1);
163}
164
165void __kprobes arch_remove_kprobe(struct kprobe *p)
166{
167	if (p->ainsn.xol_insn) {
168		free_insn_slot(p->ainsn.xol_insn, 0);
169		p->ainsn.xol_insn = NULL;
170	}
171}
172
173static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
174{
175	kcb->prev_kprobe.kp = kprobe_running();
176	kcb->prev_kprobe.status = kcb->kprobe_status;
177}
178
179static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
180{
181	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
182	kcb->kprobe_status = kcb->prev_kprobe.status;
183}
184
185static void __kprobes set_current_kprobe(struct kprobe *p)
186{
187	__this_cpu_write(current_kprobe, p);
188}
189
190/*
191 * Mask all of DAIF while executing the instruction out-of-line, to keep things
192 * simple and avoid nesting exceptions. Interrupts do have to be disabled since
193 * the kprobe state is per-CPU and doesn't get migrated.
194 */
195static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
196						struct pt_regs *regs)
197{
198	kcb->saved_irqflag = regs->pstate & DAIF_MASK;
199	regs->pstate |= DAIF_MASK;
200}
201
202static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
203						struct pt_regs *regs)
204{
205	regs->pstate &= ~DAIF_MASK;
206	regs->pstate |= kcb->saved_irqflag;
207}
208
209static void __kprobes setup_singlestep(struct kprobe *p,
210				       struct pt_regs *regs,
211				       struct kprobe_ctlblk *kcb, int reenter)
212{
213	unsigned long slot;
214
215	if (reenter) {
216		save_previous_kprobe(kcb);
217		set_current_kprobe(p);
218		kcb->kprobe_status = KPROBE_REENTER;
219	} else {
220		kcb->kprobe_status = KPROBE_HIT_SS;
221	}
222
223
224	if (p->ainsn.xol_insn) {
225		/* prepare for single stepping */
226		slot = (unsigned long)p->ainsn.xol_insn;
227
228		kprobes_save_local_irqflag(kcb, regs);
229		instruction_pointer_set(regs, slot);
230	} else {
231		/* insn simulation */
232		arch_simulate_insn(p, regs);
233	}
234}
235
236static int __kprobes reenter_kprobe(struct kprobe *p,
237				    struct pt_regs *regs,
238				    struct kprobe_ctlblk *kcb)
239{
240	switch (kcb->kprobe_status) {
241	case KPROBE_HIT_SSDONE:
242	case KPROBE_HIT_ACTIVE:
243		kprobes_inc_nmissed_count(p);
244		setup_singlestep(p, regs, kcb, 1);
245		break;
246	case KPROBE_HIT_SS:
247	case KPROBE_REENTER:
248		pr_warn("Failed to recover from reentered kprobes.\n");
249		dump_kprobe(p);
250		BUG();
251		break;
252	default:
253		WARN_ON(1);
254		return 0;
255	}
256
257	return 1;
258}
259
260static void __kprobes
261post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb, struct pt_regs *regs)
262{
263	/* return addr restore if non-branching insn */
264	if (cur->ainsn.xol_restore != 0)
265		instruction_pointer_set(regs, cur->ainsn.xol_restore);
266
267	/* restore back original saved kprobe variables and continue */
268	if (kcb->kprobe_status == KPROBE_REENTER) {
269		restore_previous_kprobe(kcb);
270		return;
271	}
272	/* call post handler */
273	kcb->kprobe_status = KPROBE_HIT_SSDONE;
274	if (cur->post_handler)
275		cur->post_handler(cur, regs, 0);
276
277	reset_current_kprobe();
278}
279
280int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
281{
282	struct kprobe *cur = kprobe_running();
283	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
284
285	switch (kcb->kprobe_status) {
286	case KPROBE_HIT_SS:
287	case KPROBE_REENTER:
288		/*
289		 * We are here because the instruction being single
290		 * stepped caused a page fault. We reset the current
291		 * kprobe and the ip points back to the probe address
292		 * and allow the page fault handler to continue as a
293		 * normal page fault.
294		 */
295		instruction_pointer_set(regs, (unsigned long) cur->addr);
296		BUG_ON(!instruction_pointer(regs));
297
298		if (kcb->kprobe_status == KPROBE_REENTER) {
299			restore_previous_kprobe(kcb);
300		} else {
301			kprobes_restore_local_irqflag(kcb, regs);
302			reset_current_kprobe();
303		}
304
305		break;
306	}
307	return 0;
308}
309
310int __kprobes
311kprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
312{
313	struct kprobe *p, *cur_kprobe;
314	struct kprobe_ctlblk *kcb;
315	unsigned long addr = instruction_pointer(regs);
316
317	kcb = get_kprobe_ctlblk();
318	cur_kprobe = kprobe_running();
319
320	p = get_kprobe((kprobe_opcode_t *) addr);
321	if (WARN_ON_ONCE(!p)) {
322		/*
323		 * Something went wrong. This BRK used an immediate reserved
324		 * for kprobes, but we couldn't find any corresponding probe.
325		 */
326		return DBG_HOOK_ERROR;
327	}
328
329	if (cur_kprobe) {
330		/* Hit a kprobe inside another kprobe */
331		if (!reenter_kprobe(p, regs, kcb))
332			return DBG_HOOK_ERROR;
333	} else {
334		/* Probe hit */
335		set_current_kprobe(p);
336		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
337
338		/*
339		 * If we have no pre-handler or it returned 0, we
340		 * continue with normal processing.  If we have a
341		 * pre-handler and it returned non-zero, it will
342		 * modify the execution path and not need to single-step
343		 * Let's just reset current kprobe and exit.
344		 */
345		if (!p->pre_handler || !p->pre_handler(p, regs))
346			setup_singlestep(p, regs, kcb, 0);
347		else
348			reset_current_kprobe();
349	}
350
351	return DBG_HOOK_HANDLED;
352}
353
354int __kprobes
355kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr)
356{
357	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
358	unsigned long addr = instruction_pointer(regs);
359	struct kprobe *cur = kprobe_running();
360
361	if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
362	    ((unsigned long)&cur->ainsn.xol_insn[1] == addr)) {
363		kprobes_restore_local_irqflag(kcb, regs);
364		post_kprobe_handler(cur, kcb, regs);
365
366		return DBG_HOOK_HANDLED;
367	}
368
369	/* not ours, kprobes should ignore it */
370	return DBG_HOOK_ERROR;
371}
372
373int __kprobes
374kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
375{
376	if (regs->pc != (unsigned long)__kretprobe_trampoline)
377		return DBG_HOOK_ERROR;
378
379	regs->pc = kretprobe_trampoline_handler(regs, (void *)regs->regs[29]);
380	return DBG_HOOK_HANDLED;
381}
382
383/*
384 * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
385 * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
386 */
387int __init arch_populate_kprobe_blacklist(void)
388{
389	int ret;
390
391	ret = kprobe_add_area_blacklist((unsigned long)__entry_text_start,
392					(unsigned long)__entry_text_end);
393	if (ret)
394		return ret;
395	ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
396					(unsigned long)__irqentry_text_end);
397	if (ret)
398		return ret;
399	ret = kprobe_add_area_blacklist((unsigned long)__hyp_text_start,
400					(unsigned long)__hyp_text_end);
401	if (ret || is_kernel_in_hyp_mode())
402		return ret;
403	ret = kprobe_add_area_blacklist((unsigned long)__hyp_idmap_text_start,
404					(unsigned long)__hyp_idmap_text_end);
405	return ret;
406}
407
408void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
409				      struct pt_regs *regs)
410{
411	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
412	ri->fp = (void *)regs->regs[29];
413
414	/* replace return addr (x30) with trampoline */
415	regs->regs[30] = (long)&__kretprobe_trampoline;
416}
417
418int __kprobes arch_trampoline_kprobe(struct kprobe *p)
419{
420	return 0;
421}
422
423int __init arch_init_kprobes(void)
424{
425	return 0;
426}