text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * arch/arm64/kernel/probes/kprobes.c
   *
   * Kprobes support for ARM64
   *
   * Copyright (C) 2013 Linaro Limited.
   * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
   */
  #include <linux/kasan.h>
  #include <linux/kernel.h>
  #include <linux/kprobes.h>
  #include <linux/extable.h>
  #include <linux/slab.h>
  #include <linux/stop_machine.h>
  #include <linux/sched/debug.h>
  #include <linux/set_memory.h>
  #include <linux/stringify.h>
  #include <linux/vmalloc.h>
  #include <asm/traps.h>
  #include <asm/ptrace.h>
  #include <asm/cacheflush.h>
  #include <asm/debug-monitors.h>
  #include <asm/daifflags.h>
  #include <asm/system_misc.h>
  #include <asm/insn.h>
  #include <linux/uaccess.h>
  #include <asm/irq.h>
  #include <asm/sections.h>
  
  #include "decode-insn.h"
  
  DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  
  static void __kprobes
  post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
  
  static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
  {
  	void *addrs[1];
  	u32 insns[1];
  
  	addrs[0] = addr;
  	insns[0] = opcode;
  
  	return aarch64_insn_patch_text(addrs, insns, 1);
  }
  
  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  {
  	/* prepare insn slot */
  	patch_text(p->ainsn.api.insn, p->opcode);
  
  	flush_icache_range((uintptr_t) (p->ainsn.api.insn),
  			   (uintptr_t) (p->ainsn.api.insn) +
  			   MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  
  	/*
  	 * Needs restoring of return address after stepping xol.
  	 */
  	p->ainsn.api.restore = (unsigned long) p->addr +
  	  sizeof(kprobe_opcode_t);
  }
  
  static void __kprobes arch_prepare_simulate(struct kprobe *p)
  {
  	/* This instructions is not executed xol. No need to adjust the PC */
  	p->ainsn.api.restore = 0;
  }
  
  static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  {
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  
  	if (p->ainsn.api.handler)
  		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
  
  	/* single step simulated, now go for post processing */
  	post_kprobe_handler(kcb, regs);
  }
  
  int __kprobes arch_prepare_kprobe(struct kprobe *p)
  {
  	unsigned long probe_addr = (unsigned long)p->addr;
  
  	if (probe_addr & 0x3)
  		return -EINVAL;
  
  	/* copy instruction */
  	p->opcode = le32_to_cpu(*p->addr);
  
  	if (search_exception_tables(probe_addr))
  		return -EINVAL;
  
  	/* decode instruction */
  	switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
  	case INSN_REJECTED:	/* insn not supported */
  		return -EINVAL;
  
  	case INSN_GOOD_NO_SLOT:	/* insn need simulation */
  		p->ainsn.api.insn = NULL;
  		break;
  
  	case INSN_GOOD:	/* instruction uses slot */
  		p->ainsn.api.insn = get_insn_slot();
  		if (!p->ainsn.api.insn)
  			return -ENOMEM;
  		break;
  	}
  
  	/* prepare the instruction */
  	if (p->ainsn.api.insn)
  		arch_prepare_ss_slot(p);
  	else
  		arch_prepare_simulate(p);
  
  	return 0;
  }
  
  void *alloc_insn_page(void)
  {
  	void *page;
  
  	page = vmalloc_exec(PAGE_SIZE);
  	if (page) {
  		set_memory_ro((unsigned long)page, 1);
  		set_vm_flush_reset_perms(page);
  	}
  
  	return page;
  }
  
  /* arm kprobe: install breakpoint in text */
  void __kprobes arch_arm_kprobe(struct kprobe *p)
  {
  	patch_text(p->addr, BRK64_OPCODE_KPROBES);
  }
  
  /* disarm kprobe: remove breakpoint from text */
  void __kprobes arch_disarm_kprobe(struct kprobe *p)
  {
  	patch_text(p->addr, p->opcode);
  }
  
  void __kprobes arch_remove_kprobe(struct kprobe *p)
  {
  	if (p->ainsn.api.insn) {
  		free_insn_slot(p->ainsn.api.insn, 0);
  		p->ainsn.api.insn = NULL;
  	}
  }
  
  static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
  {
  	kcb->prev_kprobe.kp = kprobe_running();
  	kcb->prev_kprobe.status = kcb->kprobe_status;
  }
  
  static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
  {
  	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
  	kcb->kprobe_status = kcb->prev_kprobe.status;
  }
  
  static void __kprobes set_current_kprobe(struct kprobe *p)
  {
  	__this_cpu_write(current_kprobe, p);
  }
  
  /*
   * Interrupts need to be disabled before single-step mode is set, and not
   * reenabled until after single-step mode ends.
   * Without disabling interrupt on local CPU, there is a chance of
   * interrupt occurrence in the period of exception return and  start of
   * out-of-line single-step, that result in wrongly single stepping
   * into the interrupt handler.
   */
  static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
  						struct pt_regs *regs)
  {
  	kcb->saved_irqflag = regs->pstate & DAIF_MASK;
  	regs->pstate |= PSR_I_BIT;
  	/* Unmask PSTATE.D for enabling software step exceptions. */
  	regs->pstate &= ~PSR_D_BIT;
  }
  
  static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
  						struct pt_regs *regs)
  {
  	regs->pstate &= ~DAIF_MASK;
  	regs->pstate |= kcb->saved_irqflag;
  }
  
  static void __kprobes
  set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
  {
  	kcb->ss_ctx.ss_pending = true;
  	kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
  }
  
  static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
  {
  	kcb->ss_ctx.ss_pending = false;
  	kcb->ss_ctx.match_addr = 0;
  }
  
  static void __kprobes setup_singlestep(struct kprobe *p,
  				       struct pt_regs *regs,
  				       struct kprobe_ctlblk *kcb, int reenter)
  {
  	unsigned long slot;
  
  	if (reenter) {
  		save_previous_kprobe(kcb);
  		set_current_kprobe(p);
  		kcb->kprobe_status = KPROBE_REENTER;
  	} else {
  		kcb->kprobe_status = KPROBE_HIT_SS;
  	}
  
  
  	if (p->ainsn.api.insn) {
  		/* prepare for single stepping */
  		slot = (unsigned long)p->ainsn.api.insn;
  
  		set_ss_context(kcb, slot);	/* mark pending ss */
  
  		/* IRQs and single stepping do not mix well. */
  		kprobes_save_local_irqflag(kcb, regs);
  		kernel_enable_single_step(regs);
  		instruction_pointer_set(regs, slot);
  	} else {
  		/* insn simulation */
  		arch_simulate_insn(p, regs);
  	}
  }
  
  static int __kprobes reenter_kprobe(struct kprobe *p,
  				    struct pt_regs *regs,
  				    struct kprobe_ctlblk *kcb)
  {
  	switch (kcb->kprobe_status) {
  	case KPROBE_HIT_SSDONE:
  	case KPROBE_HIT_ACTIVE:
  		kprobes_inc_nmissed_count(p);
  		setup_singlestep(p, regs, kcb, 1);
  		break;
  	case KPROBE_HIT_SS:
  	case KPROBE_REENTER:
  		pr_warn("Unrecoverable kprobe detected.\n");
  		dump_kprobe(p);
  		BUG();
  		break;
  	default:
  		WARN_ON(1);
  		return 0;
  	}
  
  	return 1;
  }
  
  static void __kprobes
  post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
  {
  	struct kprobe *cur = kprobe_running();
  
  	if (!cur)
  		return;
  
  	/* return addr restore if non-branching insn */
  	if (cur->ainsn.api.restore != 0)
  		instruction_pointer_set(regs, cur->ainsn.api.restore);
  
  	/* restore back original saved kprobe variables and continue */
  	if (kcb->kprobe_status == KPROBE_REENTER) {
  		restore_previous_kprobe(kcb);
  		return;
  	}
  	/* call post handler */
  	kcb->kprobe_status = KPROBE_HIT_SSDONE;
  	if (cur->post_handler)	{
  		/* post_handler can hit breakpoint and single step
  		 * again, so we enable D-flag for recursive exception.
  		 */
  		cur->post_handler(cur, regs, 0);
  	}
  
  	reset_current_kprobe();
  }
  
  int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
  {
  	struct kprobe *cur = kprobe_running();
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  
  	switch (kcb->kprobe_status) {
  	case KPROBE_HIT_SS:
  	case KPROBE_REENTER:
  		/*
  		 * We are here because the instruction being single
  		 * stepped caused a page fault. We reset the current
  		 * kprobe and the ip points back to the probe address
  		 * and allow the page fault handler to continue as a
  		 * normal page fault.
  		 */
  		instruction_pointer_set(regs, (unsigned long) cur->addr);
  		if (!instruction_pointer(regs))
  			BUG();
  
  		kernel_disable_single_step();
  
  		if (kcb->kprobe_status == KPROBE_REENTER)
  			restore_previous_kprobe(kcb);
  		else
  			reset_current_kprobe();
  
  		break;
  	case KPROBE_HIT_ACTIVE:
  	case KPROBE_HIT_SSDONE:
  		/*
  		 * We increment the nmissed count for accounting,
  		 * we can also use npre/npostfault count for accounting
  		 * these specific fault cases.
  		 */
  		kprobes_inc_nmissed_count(cur);
  
  		/*
  		 * We come here because instructions in the pre/post
  		 * handler caused the page_fault, this could happen
  		 * if handler tries to access user space by
  		 * copy_from_user(), get_user() etc. Let the
  		 * user-specified handler try to fix it first.
  		 */
  		if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
  			return 1;
  
  		/*
  		 * In case the user-specified fault handler returned
  		 * zero, try to fix up.
  		 */
  		if (fixup_exception(regs))
  			return 1;
  	}
  	return 0;
  }
  
  static void __kprobes kprobe_handler(struct pt_regs *regs)
  {
  	struct kprobe *p, *cur_kprobe;
  	struct kprobe_ctlblk *kcb;
  	unsigned long addr = instruction_pointer(regs);
  
  	kcb = get_kprobe_ctlblk();
  	cur_kprobe = kprobe_running();
  
  	p = get_kprobe((kprobe_opcode_t *) addr);
  
  	if (p) {
  		if (cur_kprobe) {
  			if (reenter_kprobe(p, regs, kcb))
  				return;
  		} else {
  			/* Probe hit */
  			set_current_kprobe(p);
  			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
  
  			/*
  			 * If we have no pre-handler or it returned 0, we
  			 * continue with normal processing.  If we have a
  			 * pre-handler and it returned non-zero, it will
  			 * modify the execution path and no need to single
  			 * stepping. Let's just reset current kprobe and exit.
  			 *
  			 * pre_handler can hit a breakpoint and can step thru
  			 * before return, keep PSTATE D-flag enabled until
  			 * pre_handler return back.
  			 */
  			if (!p->pre_handler || !p->pre_handler(p, regs)) {
  				setup_singlestep(p, regs, kcb, 0);
  			} else
  				reset_current_kprobe();
  		}
  	}
  	/*
  	 * The breakpoint instruction was removed right
  	 * after we hit it.  Another cpu has removed
  	 * either a probepoint or a debugger breakpoint
  	 * at this address.  In either case, no further
  	 * handling of this interrupt is appropriate.
  	 * Return back to original instruction, and continue.
  	 */
  }
  
  static int __kprobes
  kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
  {
  	if ((kcb->ss_ctx.ss_pending)
  	    && (kcb->ss_ctx.match_addr == addr)) {
  		clear_ss_context(kcb);	/* clear pending ss */
  		return DBG_HOOK_HANDLED;
  	}
  	/* not ours, kprobes should ignore it */
  	return DBG_HOOK_ERROR;
  }
  
  static int __kprobes
  kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
  {
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  	int retval;
  
  	/* return error if this is not our step */
  	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
  
  	if (retval == DBG_HOOK_HANDLED) {
  		kprobes_restore_local_irqflag(kcb, regs);
  		kernel_disable_single_step();
  
  		post_kprobe_handler(kcb, regs);
  	}
  
  	return retval;
  }
  
  static struct step_hook kprobes_step_hook = {
  	.fn = kprobe_single_step_handler,
  };
  
  static int __kprobes
  kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
  {
  	kprobe_handler(regs);
  	return DBG_HOOK_HANDLED;
  }
  
  static struct break_hook kprobes_break_hook = {
  	.imm = KPROBES_BRK_IMM,
  	.fn = kprobe_breakpoint_handler,
  };
  
  /*
   * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
   * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
   */
  int __init arch_populate_kprobe_blacklist(void)
  {
  	int ret;
  
  	ret = kprobe_add_area_blacklist((unsigned long)__entry_text_start,
  					(unsigned long)__entry_text_end);
  	if (ret)
  		return ret;
  	ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
  					(unsigned long)__irqentry_text_end);
  	if (ret)
  		return ret;
  	ret = kprobe_add_area_blacklist((unsigned long)__idmap_text_start,
  					(unsigned long)__idmap_text_end);
  	if (ret)
  		return ret;
  	ret = kprobe_add_area_blacklist((unsigned long)__hyp_text_start,
  					(unsigned long)__hyp_text_end);
  	if (ret || is_kernel_in_hyp_mode())
  		return ret;
  	ret = kprobe_add_area_blacklist((unsigned long)__hyp_idmap_text_start,
  					(unsigned long)__hyp_idmap_text_end);
  	return ret;
  }
  
  void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
  {
  	struct kretprobe_instance *ri = NULL;
  	struct hlist_head *head, empty_rp;
  	struct hlist_node *tmp;
  	unsigned long flags, orig_ret_address = 0;
  	unsigned long trampoline_address =
  		(unsigned long)&kretprobe_trampoline;
  	kprobe_opcode_t *correct_ret_addr = NULL;
  
  	INIT_HLIST_HEAD(&empty_rp);
  	kretprobe_hash_lock(current, &head, &flags);
  
  	/*
  	 * It is possible to have multiple instances associated with a given
  	 * task either because multiple functions in the call path have
  	 * return probes installed on them, and/or more than one
  	 * return probe was registered for a target function.
  	 *
  	 * We can handle this because:
  	 *     - instances are always pushed into the head of the list
  	 *     - when multiple return probes are registered for the same
  	 *	 function, the (chronologically) first instance's ret_addr
  	 *	 will be the real return address, and all the rest will
  	 *	 point to kretprobe_trampoline.
  	 */
  	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
  		if (ri->task != current)
  			/* another task is sharing our hash bucket */
  			continue;
  
  		orig_ret_address = (unsigned long)ri->ret_addr;
  
  		if (orig_ret_address != trampoline_address)
  			/*
  			 * This is the real return address. Any other
  			 * instances associated with this task are for
  			 * other calls deeper on the call stack
  			 */
  			break;
  	}
  
  	kretprobe_assert(ri, orig_ret_address, trampoline_address);
  
  	correct_ret_addr = ri->ret_addr;
  	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
  		if (ri->task != current)
  			/* another task is sharing our hash bucket */
  			continue;
  
  		orig_ret_address = (unsigned long)ri->ret_addr;
  		if (ri->rp && ri->rp->handler) {
  			__this_cpu_write(current_kprobe, &ri->rp->kp);
  			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
  			ri->ret_addr = correct_ret_addr;
  			ri->rp->handler(ri, regs);
  			__this_cpu_write(current_kprobe, NULL);
  		}
  
  		recycle_rp_inst(ri, &empty_rp);
  
  		if (orig_ret_address != trampoline_address)
  			/*
  			 * This is the real return address. Any other
  			 * instances associated with this task are for
  			 * other calls deeper on the call stack
  			 */
  			break;
  	}
  
  	kretprobe_hash_unlock(current, &flags);
  
  	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
  		hlist_del(&ri->hlist);
  		kfree(ri);
  	}
  	return (void *)orig_ret_address;
  }
  
  void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
  				      struct pt_regs *regs)
  {
  	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
  
  	/* replace return addr (x30) with trampoline */
  	regs->regs[30] = (long)&kretprobe_trampoline;
  }
  
  int __kprobes arch_trampoline_kprobe(struct kprobe *p)
  {
  	return 0;
  }
  
  int __init arch_init_kprobes(void)
  {
  	register_kernel_break_hook(&kprobes_break_hook);
  	register_kernel_step_hook(&kprobes_step_hook);
  
  	return 0;
  }
  