text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   */
  
  #include <linux/mm.h>
  #include <linux/sched/signal.h>
  #include <linux/hardirq.h>
  #include <linux/module.h>
  #include <linux/uaccess.h>
  #include <linux/sched/debug.h>
  #include <asm/current.h>
  #include <asm/tlbflush.h>
  #include <arch.h>
  #include <as-layout.h>
  #include <kern_util.h>
  #include <os.h>
  #include <skas.h>
  
  /*
   * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
   * segv().
   */
  int handle_page_fault(unsigned long address, unsigned long ip,
  		      int is_write, int is_user, int *code_out)
  {
  	struct mm_struct *mm = current->mm;
  	struct vm_area_struct *vma;
  	pmd_t *pmd;
  	pte_t *pte;
  	int err = -EFAULT;
  	unsigned int flags = FAULT_FLAG_DEFAULT;
  
  	*code_out = SEGV_MAPERR;
  
  	/*
  	 * If the fault was with pagefaults disabled, don't take the fault, just
  	 * fail.
  	 */
  	if (faulthandler_disabled())
  		goto out_nosemaphore;
  
  	if (is_user)
  		flags |= FAULT_FLAG_USER;
  retry:
  	mmap_read_lock(mm);
  	vma = find_vma(mm, address);
  	if (!vma)
  		goto out;
  	else if (vma->vm_start <= address)
  		goto good_area;
  	else if (!(vma->vm_flags & VM_GROWSDOWN))
  		goto out;
  	else if (is_user && !ARCH_IS_STACKGROW(address))
  		goto out;
  	else if (expand_stack(vma, address))
  		goto out;
  
  good_area:
  	*code_out = SEGV_ACCERR;
  	if (is_write) {
  		if (!(vma->vm_flags & VM_WRITE))
  			goto out;
  		flags |= FAULT_FLAG_WRITE;
  	} else {
  		/* Don't require VM_READ|VM_EXEC for write faults! */
  		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
  			goto out;
  	}
  
  	do {
  		vm_fault_t fault;
  
  		fault = handle_mm_fault(vma, address, flags, NULL);
  
  		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
  			goto out_nosemaphore;
  
  		if (unlikely(fault & VM_FAULT_ERROR)) {
  			if (fault & VM_FAULT_OOM) {
  				goto out_of_memory;
  			} else if (fault & VM_FAULT_SIGSEGV) {
  				goto out;
  			} else if (fault & VM_FAULT_SIGBUS) {
  				err = -EACCES;
  				goto out;
  			}
  			BUG();
  		}
  		if (fault & VM_FAULT_RETRY) {
  			flags |= FAULT_FLAG_TRIED;
  
  			goto retry;
  		}
  
  		pmd = pmd_off(mm, address);
  		pte = pte_offset_kernel(pmd, address);
  	} while (!pte_present(*pte));
  	err = 0;
  	/*
  	 * The below warning was added in place of
  	 *	pte_mkyoung(); if (is_write) pte_mkdirty();
  	 * If it's triggered, we'd see normally a hang here (a clean pte is
  	 * marked read-only to emulate the dirty bit).
  	 * However, the generic code can mark a PTE writable but clean on a
  	 * concurrent read fault, triggering this harmlessly. So comment it out.
  	 */
  #if 0
  	WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
  #endif
  	flush_tlb_page(vma, address);
  out:
  	mmap_read_unlock(mm);
  out_nosemaphore:
  	return err;
  
  out_of_memory:
  	/*
  	 * We ran out of memory, call the OOM killer, and return the userspace
  	 * (which will retry the fault, or kill us if we got oom-killed).
  	 */
  	mmap_read_unlock(mm);
  	if (!is_user)
  		goto out_nosemaphore;
  	pagefault_out_of_memory();
  	return 0;
  }
  
  static void show_segv_info(struct uml_pt_regs *regs)
  {
  	struct task_struct *tsk = current;
  	struct faultinfo *fi = UPT_FAULTINFO(regs);
  
  	if (!unhandled_signal(tsk, SIGSEGV))
  		return;
  
  	if (!printk_ratelimit())
  		return;
  
  	printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
  		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
  		tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
  		(void *)UPT_IP(regs), (void *)UPT_SP(regs),
  		fi->error_code);
  
  	print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
  	printk(KERN_CONT "\n");
  }
  
  static void bad_segv(struct faultinfo fi, unsigned long ip)
  {
  	current->thread.arch.faultinfo = fi;
  	force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
  }
  
  void fatal_sigsegv(void)
  {
  	force_fatal_sig(SIGSEGV);
  	do_signal(&current->thread.regs);
  	/*
  	 * This is to tell gcc that we're not returning - do_signal
  	 * can, in general, return, but in this case, it's not, since
  	 * we just got a fatal SIGSEGV queued.
  	 */
  	os_dump_core();
  }
  
  /**
   * segv_handler() - the SIGSEGV handler
   * @sig:	the signal number
   * @unused_si:	the signal info struct; unused in this handler
   * @regs:	the ptrace register information
   *
   * The handler first extracts the faultinfo from the UML ptrace regs struct.
   * If the userfault did not happen in an UML userspace process, bad_segv is called.
   * Otherwise the signal did happen in a cloned userspace process, handle it.
   */
  void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
  {
  	struct faultinfo * fi = UPT_FAULTINFO(regs);
  
  	if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
  		show_segv_info(regs);
  		bad_segv(*fi, UPT_IP(regs));
  		return;
  	}
  	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
  }
  
  /*
   * We give a *copy* of the faultinfo in the regs to segv.
   * This must be done, since nesting SEGVs could overwrite
   * the info in the regs. A pointer to the info then would
   * give us bad data!
   */
  unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
  		   struct uml_pt_regs *regs)
  {
  	jmp_buf *catcher;
  	int si_code;
  	int err;
  	int is_write = FAULT_WRITE(fi);
  	unsigned long address = FAULT_ADDRESS(fi);
  
  	if (!is_user && regs)
  		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
  
  	if (!is_user && (address >= start_vm) && (address < end_vm)) {
  		flush_tlb_kernel_vm();
  		goto out;
  	}
  	else if (current->mm == NULL) {
  		show_regs(container_of(regs, struct pt_regs, regs));
  		panic("Segfault with no mm");
  	}
  	else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
  		show_regs(container_of(regs, struct pt_regs, regs));
  		panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
  		       address, ip);
  	}
  
  	if (SEGV_IS_FIXABLE(&fi))
  		err = handle_page_fault(address, ip, is_write, is_user,
  					&si_code);
  	else {
  		err = -EFAULT;
  		/*
  		 * A thread accessed NULL, we get a fault, but CR2 is invalid.
  		 * This code is used in __do_copy_from_user() of TT mode.
  		 * XXX tt mode is gone, so maybe this isn't needed any more
  		 */
  		address = 0;
  	}
  
  	catcher = current->thread.fault_catcher;
  	if (!err)
  		goto out;
  	else if (catcher != NULL) {
  		current->thread.fault_addr = (void *) address;
  		UML_LONGJMP(catcher, 1);
  	}
  	else if (current->thread.fault_addr != NULL)
  		panic("fault_addr set but no fault catcher");
  	else if (!is_user && arch_fixup(ip, regs))
  		goto out;
  
  	if (!is_user) {
  		show_regs(container_of(regs, struct pt_regs, regs));
  		panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
  		      address, ip);
  	}
  
  	show_segv_info(regs);
  
  	if (err == -EACCES) {
  		current->thread.arch.faultinfo = fi;
  		force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
  	} else {
  		BUG_ON(err != -EFAULT);
  		current->thread.arch.faultinfo = fi;
  		force_sig_fault(SIGSEGV, si_code, (void __user *) address);
  	}
  
  out:
  	if (regs)
  		current->thread.segv_regs = NULL;
  
  	return 0;
  }
  
  void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
  {
  	int code, err;
  	if (!UPT_IS_USER(regs)) {
  		if (sig == SIGBUS)
  			printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
  			       "mount likely just ran out of space\n");
  		panic("Kernel mode signal %d", sig);
  	}
  
  	arch_examine_signal(sig, regs);
  
  	/* Is the signal layout for the signal known?
  	 * Signal data must be scrubbed to prevent information leaks.
  	 */
  	code = si->si_code;
  	err = si->si_errno;
  	if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
  		struct faultinfo *fi = UPT_FAULTINFO(regs);
  		current->thread.arch.faultinfo = *fi;
  		force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
  	} else {
  		printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
  		       sig, code, err);
  		force_sig(sig);
  	}
  }
  
  void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
  {
  	if (current->thread.fault_catcher != NULL)
  		UML_LONGJMP(current->thread.fault_catcher, 1);
  	else
  		relay_signal(sig, si, regs);
  }
  
  void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
  {
  	do_IRQ(WINCH_IRQ, regs);
  }
  