text: /*
   *  linux/arch/arm/mm/fault.c
   *
   *  Copyright (C) 1995  Linus Torvalds
   *  Modifications for ARM processor (c) 1995-2004 Russell King
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   */
  #include <linux/extable.h>
  #include <linux/signal.h>
  #include <linux/mm.h>
  #include <linux/hardirq.h>
  #include <linux/init.h>
  #include <linux/kprobes.h>
  #include <linux/uaccess.h>
  #include <linux/page-flags.h>
  #include <linux/sched/signal.h>
  #include <linux/sched/debug.h>
  #include <linux/highmem.h>
  #include <linux/perf_event.h>
  
  #include <asm/pgtable.h>
  #include <asm/system_misc.h>
  #include <asm/system_info.h>
  #include <asm/tlbflush.h>
  
  #include "fault.h"
  
  #ifdef CONFIG_MMU
  
  #ifdef CONFIG_KPROBES
  static inline int notify_page_fault(struct pt_regs *regs, unsigned int fsr)
  {
  	int ret = 0;
  
  	if (!user_mode(regs)) {
  		/* kprobe_running() needs smp_processor_id() */
  		preempt_disable();
  		if (kprobe_running() && kprobe_fault_handler(regs, fsr))
  			ret = 1;
  		preempt_enable();
  	}
  
  	return ret;
  }
  #else
  static inline int notify_page_fault(struct pt_regs *regs, unsigned int fsr)
  {
  	return 0;
  }
  #endif
  
  /*
   * This is useful to dump out the page tables associated with
   * 'addr' in mm 'mm'.
   */
  void show_pte(struct mm_struct *mm, unsigned long addr)
  {
  	pgd_t *pgd;
  
  	if (!mm)
  		mm = &init_mm;
  
  	pr_alert("pgd = %p\n", mm->pgd);
  	pgd = pgd_offset(mm, addr);
  	pr_alert("[%08lx] *pgd=%08llx",
  			addr, (long long)pgd_val(*pgd));
  
  	do {
  		pud_t *pud;
  		pmd_t *pmd;
  		pte_t *pte;
  
  		if (pgd_none(*pgd))
  			break;
  
  		if (pgd_bad(*pgd)) {
  			pr_cont("(bad)");
  			break;
  		}
  
  		pud = pud_offset(pgd, addr);
  		if (PTRS_PER_PUD != 1)
  			pr_cont(", *pud=%08llx", (long long)pud_val(*pud));
  
  		if (pud_none(*pud))
  			break;
  
  		if (pud_bad(*pud)) {
  			pr_cont("(bad)");
  			break;
  		}
  
  		pmd = pmd_offset(pud, addr);
  		if (PTRS_PER_PMD != 1)
  			pr_cont(", *pmd=%08llx", (long long)pmd_val(*pmd));
  
  		if (pmd_none(*pmd))
  			break;
  
  		if (pmd_bad(*pmd)) {
  			pr_cont("(bad)");
  			break;
  		}
  
  		/* We must not map this if we have highmem enabled */
  		if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
  			break;
  
  		pte = pte_offset_map(pmd, addr);
  		pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
  #ifndef CONFIG_ARM_LPAE
  		pr_cont(", *ppte=%08llx",
  		       (long long)pte_val(pte[PTE_HWTABLE_PTRS]));
  #endif
  		pte_unmap(pte);
  	} while(0);
  
  	pr_cont("\n");
  }
  #else					/* CONFIG_MMU */
  void show_pte(struct mm_struct *mm, unsigned long addr)
  { }
  #endif					/* CONFIG_MMU */
  
  /*
   * Oops.  The kernel tried to access some page that wasn't present.
   */
  static void
  __do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
  		  struct pt_regs *regs)
  {
  	/*
  	 * Are we prepared to handle this kernel fault?
  	 */
  	if (fixup_exception(regs))
  		return;
  
  	/*
  	 * No handler, we'll have to terminate things with extreme prejudice.
  	 */
  	bust_spinlocks(1);
  	pr_alert("Unable to handle kernel %s at virtual address %08lx\n",
  		 (addr < PAGE_SIZE) ? "NULL pointer dereference" :
  		 "paging request", addr);
  
  	show_pte(mm, addr);
  	die("Oops", regs, fsr);
  	bust_spinlocks(0);
  	do_exit(SIGKILL);
  }
  
  /*
   * Something tried to access memory that isn't in our memory map..
   * User mode accesses just cause a SIGSEGV
   */
  static void
  __do_user_fault(struct task_struct *tsk, unsigned long addr,
  		unsigned int fsr, unsigned int sig, int code,
  		struct pt_regs *regs)
  {
  	struct siginfo si;
  
  #ifdef CONFIG_DEBUG_USER
  	if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
  	    ((user_debug & UDBG_BUS)  && (sig == SIGBUS))) {
  		printk(KERN_DEBUG "%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
  		       tsk->comm, sig, addr, fsr);
  		show_pte(tsk->mm, addr);
  		show_regs(regs);
  	}
  #endif
  
  	tsk->thread.address = addr;
  	tsk->thread.error_code = fsr;
  	tsk->thread.trap_no = 14;
  	si.si_signo = sig;
  	si.si_errno = 0;
  	si.si_code = code;
  	si.si_addr = (void __user *)addr;
  	force_sig_info(sig, &si, tsk);
  }
  
  void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
  {
  	struct task_struct *tsk = current;
  	struct mm_struct *mm = tsk->active_mm;
  
  	/*
  	 * If we are in kernel mode at this point, we
  	 * have no context to handle this fault with.
  	 */
  	if (user_mode(regs))
  		__do_user_fault(tsk, addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
  	else
  		__do_kernel_fault(mm, addr, fsr, regs);
  }
  
  #ifdef CONFIG_MMU
  #define VM_FAULT_BADMAP		0x010000
  #define VM_FAULT_BADACCESS	0x020000
  
  /*
   * Check that the permissions on the VMA allow for the fault which occurred.
   * If we encountered a write fault, we must have write permission, otherwise
   * we allow any permission.
   */
  static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
  {
  	unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
  
  	if (fsr & FSR_WRITE)
  		mask = VM_WRITE;
  	if (fsr & FSR_LNX_PF)
  		mask = VM_EXEC;
  
  	return vma->vm_flags & mask ? false : true;
  }
  
  static int __kprobes
  __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
  		unsigned int flags, struct task_struct *tsk)
  {
  	struct vm_area_struct *vma;
  	int fault;
  
  	vma = find_vma(mm, addr);
  	fault = VM_FAULT_BADMAP;
  	if (unlikely(!vma))
  		goto out;
  	if (unlikely(vma->vm_start > addr))
  		goto check_stack;
  
  	/*
  	 * Ok, we have a good vm_area for this
  	 * memory access, so we can handle it.
  	 */
  good_area:
  	if (access_error(fsr, vma)) {
  		fault = VM_FAULT_BADACCESS;
  		goto out;
  	}
  
  	return handle_mm_fault(vma, addr & PAGE_MASK, flags);
  
  check_stack:
  	/* Don't allow expansion below FIRST_USER_ADDRESS */
  	if (vma->vm_flags & VM_GROWSDOWN &&
  	    addr >= FIRST_USER_ADDRESS && !expand_stack(vma, addr))
  		goto good_area;
  out:
  	return fault;
  }
  
  static int __kprobes
  do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
  {
  	struct task_struct *tsk;
  	struct mm_struct *mm;
  	int fault, sig, code;
  	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
  
  	if (notify_page_fault(regs, fsr))
  		return 0;
  
  	tsk = current;
  	mm  = tsk->mm;
  
  	/* Enable interrupts if they were enabled in the parent context. */
  	if (interrupts_enabled(regs))
  		local_irq_enable();
  
  	/*
  	 * If we're in an interrupt or have no user
  	 * context, we must not take the fault..
  	 */
  	if (faulthandler_disabled() || !mm)
  		goto no_context;
  
  	if (user_mode(regs))
  		flags |= FAULT_FLAG_USER;
  	if (fsr & FSR_WRITE)
  		flags |= FAULT_FLAG_WRITE;
  
  	/*
  	 * As per x86, we may deadlock here.  However, since the kernel only
  	 * validly references user space from well defined areas of the code,
  	 * we can bug out early if this is from code which shouldn't.
  	 */
  	if (!down_read_trylock(&mm->mmap_sem)) {
  		if (!user_mode(regs) && !search_exception_tables(regs->ARM_pc))
  			goto no_context;
  retry:
  		down_read(&mm->mmap_sem);
  	} else {
  		/*
  		 * The above down_read_trylock() might have succeeded in
  		 * which case, we'll have missed the might_sleep() from
  		 * down_read()
  		 */
  		might_sleep();
  #ifdef CONFIG_DEBUG_VM
  		if (!user_mode(regs) &&
  		    !search_exception_tables(regs->ARM_pc))
  			goto no_context;
  #endif
  	}
  
  	fault = __do_page_fault(mm, addr, fsr, flags, tsk);
  
  	/* If we need to retry but a fatal signal is pending, handle the
  	 * signal first. We do not need to release the mmap_sem because
  	 * it would already be released in __lock_page_or_retry in
  	 * mm/filemap.c. */
  	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
  		if (!user_mode(regs))
  			goto no_context;
  		return 0;
  	}
  
  	/*
  	 * Major/minor page fault accounting is only done on the
  	 * initial attempt. If we go through a retry, it is extremely
  	 * likely that the page will be found in page cache at that point.
  	 */
  
  	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
  	if (!(fault & VM_FAULT_ERROR) && flags & FAULT_FLAG_ALLOW_RETRY) {
  		if (fault & VM_FAULT_MAJOR) {
  			tsk->maj_flt++;
  			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
  					regs, addr);
  		} else {
  			tsk->min_flt++;
  			perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
  					regs, addr);
  		}
  		if (fault & VM_FAULT_RETRY) {
  			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
  			* of starvation. */
  			flags &= ~FAULT_FLAG_ALLOW_RETRY;
  			flags |= FAULT_FLAG_TRIED;
  			goto retry;
  		}
  	}
  
  	up_read(&mm->mmap_sem);
  
  	/*
  	 * Handle the "normal" case first - VM_FAULT_MAJOR
  	 */
  	if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
  		return 0;
  
  	/*
  	 * If we are in kernel mode at this point, we
  	 * have no context to handle this fault with.
  	 */
  	if (!user_mode(regs))
  		goto no_context;
  
  	if (fault & VM_FAULT_OOM) {
  		/*
  		 * We ran out of memory, call the OOM killer, and return to
  		 * userspace (which will retry the fault, or kill us if we
  		 * got oom-killed)
  		 */
  		pagefault_out_of_memory();
  		return 0;
  	}
  
  	if (fault & VM_FAULT_SIGBUS) {
  		/*
  		 * We had some memory, but were unable to
  		 * successfully fix up this page fault.
  		 */
  		sig = SIGBUS;
  		code = BUS_ADRERR;
  	} else {
  		/*
  		 * Something tried to access memory that
  		 * isn't in our memory map..
  		 */
  		sig = SIGSEGV;
  		code = fault == VM_FAULT_BADACCESS ?
  			SEGV_ACCERR : SEGV_MAPERR;
  	}
  
  	__do_user_fault(tsk, addr, fsr, sig, code, regs);
  	return 0;
  
  no_context:
  	__do_kernel_fault(mm, addr, fsr, regs);
  	return 0;
  }
  #else					/* CONFIG_MMU */
  static int
  do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
  {
  	return 0;
  }
  #endif					/* CONFIG_MMU */
  
  /*
   * First Level Translation Fault Handler
   *
   * We enter here because the first level page table doesn't contain
   * a valid entry for the address.
   *
   * If the address is in kernel space (>= TASK_SIZE), then we are
   * probably faulting in the vmalloc() area.
   *
   * If the init_task's first level page tables contains the relevant
   * entry, we copy the it to this task.  If not, we send the process
   * a signal, fixup the exception, or oops the kernel.
   *
   * NOTE! We MUST NOT take any locks for this case. We may be in an
   * interrupt or a critical region, and should only copy the information
   * from the master page table, nothing more.
   */
  #ifdef CONFIG_MMU
  static int __kprobes
  do_translation_fault(unsigned long addr, unsigned int fsr,
  		     struct pt_regs *regs)
  {
  	unsigned int index;
  	pgd_t *pgd, *pgd_k;
  	pud_t *pud, *pud_k;
  	pmd_t *pmd, *pmd_k;
  
  	if (addr < TASK_SIZE)
  		return do_page_fault(addr, fsr, regs);
  
  	if (user_mode(regs))
  		goto bad_area;
  
  	index = pgd_index(addr);
  
  	pgd = cpu_get_pgd() + index;
  	pgd_k = init_mm.pgd + index;
  
  	if (pgd_none(*pgd_k))
  		goto bad_area;
  	if (!pgd_present(*pgd))
  		set_pgd(pgd, *pgd_k);
  
  	pud = pud_offset(pgd, addr);
  	pud_k = pud_offset(pgd_k, addr);
  
  	if (pud_none(*pud_k))
  		goto bad_area;
  	if (!pud_present(*pud))
  		set_pud(pud, *pud_k);
  
  	pmd = pmd_offset(pud, addr);
  	pmd_k = pmd_offset(pud_k, addr);
  
  #ifdef CONFIG_ARM_LPAE
  	/*
  	 * Only one hardware entry per PMD with LPAE.
  	 */
  	index = 0;
  #else
  	/*
  	 * On ARM one Linux PGD entry contains two hardware entries (see page
  	 * tables layout in pgtable.h). We normally guarantee that we always
  	 * fill both L1 entries. But create_mapping() doesn't follow the rule.
  	 * It can create inidividual L1 entries, so here we have to call
  	 * pmd_none() check for the entry really corresponded to address, not
  	 * for the first of pair.
  	 */
  	index = (addr >> SECTION_SHIFT) & 1;
  #endif
  	if (pmd_none(pmd_k[index]))
  		goto bad_area;
  
  	copy_pmd(pmd, pmd_k);
  	return 0;
  
  bad_area:
  	do_bad_area(addr, fsr, regs);
  	return 0;
  }
  #else					/* CONFIG_MMU */
  static int
  do_translation_fault(unsigned long addr, unsigned int fsr,
  		     struct pt_regs *regs)
  {
  	return 0;
  }
  #endif					/* CONFIG_MMU */
  
  /*
   * Some section permission faults need to be handled gracefully.
   * They can happen due to a __{get,put}_user during an oops.
   */
  #ifndef CONFIG_ARM_LPAE
  static int
  do_sect_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
  {
  	do_bad_area(addr, fsr, regs);
  	return 0;
  }
  #endif /* CONFIG_ARM_LPAE */
  
  /*
   * This abort handler always returns "fault".
   */
  static int
  do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
  {
  	return 1;
  }
  
  struct fsr_info {
  	int	(*fn)(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
  	int	sig;
  	int	code;
  	const char *name;
  };
  
  /* FSR definition */
  #ifdef CONFIG_ARM_LPAE
  #include "fsr-3level.c"
  #else
  #include "fsr-2level.c"
  #endif
  
  void __init
  hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
  		int sig, int code, const char *name)
  {
  	if (nr < 0 || nr >= ARRAY_SIZE(fsr_info))
  		BUG();
  
  	fsr_info[nr].fn   = fn;
  	fsr_info[nr].sig  = sig;
  	fsr_info[nr].code = code;
  	fsr_info[nr].name = name;
  }
  
  /*
   * Dispatch a data abort to the relevant handler.
   */
  asmlinkage void
  do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
  {
  	const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
  	struct siginfo info;
  
  	if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
  		return;
  
  	pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
  		inf->name, fsr, addr);
  	show_pte(current->mm, addr);
  
  	info.si_signo = inf->sig;
  	info.si_errno = 0;
  	info.si_code  = inf->code;
  	info.si_addr  = (void __user *)addr;
  	arm_notify_die("", regs, &info, fsr, 0);
  }
  
  void __init
  hook_ifault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
  		 int sig, int code, const char *name)
  {
  	if (nr < 0 || nr >= ARRAY_SIZE(ifsr_info))
  		BUG();
  
  	ifsr_info[nr].fn   = fn;
  	ifsr_info[nr].sig  = sig;
  	ifsr_info[nr].code = code;
  	ifsr_info[nr].name = name;
  }
  
  asmlinkage void
  do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
  {
  	const struct fsr_info *inf = ifsr_info + fsr_fs(ifsr);
  	struct siginfo info;
  
  	if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
  		return;
  
  	pr_alert("Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
  		inf->name, ifsr, addr);
  
  	info.si_signo = inf->sig;
  	info.si_errno = 0;
  	info.si_code  = inf->code;
  	info.si_addr  = (void __user *)addr;
  	arm_notify_die("", regs, &info, ifsr, 0);
  }
  
  /*
   * Abort handler to be used only during first unmasking of asynchronous aborts
   * on the boot CPU. This makes sure that the machine will not die if the
   * firmware/bootloader left an imprecise abort pending for us to trip over.
   */
  static int __init early_abort_handler(unsigned long addr, unsigned int fsr,
  				      struct pt_regs *regs)
  {
  	pr_warn("Hit pending asynchronous external abort (FSR=0x%08x) during "
  		"first unmask, this is most likely caused by a "
  		"firmware/bootloader bug.\n", fsr);
  
  	return 0;
  }
  
  void __init early_abt_enable(void)
  {
  	fsr_info[FSR_FS_AEA].fn = early_abort_handler;
  	local_abt_enable();
  	fsr_info[FSR_FS_AEA].fn = do_bad;
  }
  
  #ifndef CONFIG_ARM_LPAE
  static int __init exceptions_init(void)
  {
  	if (cpu_architecture() >= CPU_ARCH_ARMv6) {
  		hook_fault_code(4, do_translation_fault, SIGSEGV, SEGV_MAPERR,
  				"I-cache maintenance fault");
  	}
  
  	if (cpu_architecture() >= CPU_ARCH_ARMv7) {
  		/*
  		 * TODO: Access flag faults introduced in ARMv6K.
  		 * Runtime check for 'K' extension is needed
  		 */
  		hook_fault_code(3, do_bad, SIGSEGV, SEGV_MAPERR,
  				"section access flag fault");
  		hook_fault_code(6, do_bad, SIGSEGV, SEGV_MAPERR,
  				"section access flag fault");
  	}
  
  	return 0;
  }
  
  arch_initcall(exceptions_init);
  #endif
  