/*
   * This implements the various checks for CONFIG_HARDENED_USERCOPY*,
   * which are designed to protect kernel memory from needless exposure
   * and overwrite under many unintended conditions. This code is based
   * on PAX_USERCOPY, which is:
   *
   * Copyright (C) 2001-2016 PaX Team, Bradley Spengler, Open Source
   * Security Inc.
   *
   * 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.
   *
   */
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <asm/sections.h>
  
  enum {
  	BAD_STACK = -1,
  	NOT_STACK = 0,
  	GOOD_FRAME,
  	GOOD_STACK,
  };
  
  /*
   * Checks if a given pointer and length is contained by the current
   * stack frame (if possible).
   *
   * Returns:
   *	NOT_STACK: not at all on the stack
   *	GOOD_FRAME: fully within a valid stack frame
   *	GOOD_STACK: fully on the stack (when can't do frame-checking)
   *	BAD_STACK: error condition (invalid stack position or bad stack frame)
   */
  static noinline int check_stack_object(const void *obj, unsigned long len)
  {
  	const void * const stack = task_stack_page(current);
  	const void * const stackend = stack + THREAD_SIZE;
  	int ret;
  
  	/* Object is not on the stack at all. */
  	if (obj + len <= stack || stackend <= obj)
  		return NOT_STACK;
  
  	/*
  	 * Reject: object partially overlaps the stack (passing the
  	 * the check above means at least one end is within the stack,
  	 * so if this check fails, the other end is outside the stack).
  	 */
  	if (obj < stack || stackend < obj + len)
  		return BAD_STACK;
  
  	/* Check if object is safely within a valid frame. */
  	ret = arch_within_stack_frames(stack, stackend, obj, len);
  	if (ret)
  		return ret;
  
  	return GOOD_STACK;
  }
  
  static void report_usercopy(const void *ptr, unsigned long len,
  			    bool to_user, const char *type)
  {
  	pr_emerg("kernel memory %s attempt detected %s %p (%s) (%lu bytes)
  ",
  		to_user ? "exposure" : "overwrite",
  		to_user ? "from" : "to", ptr, type ? : "unknown", len);
  	/*
  	 * For greater effect, it would be nice to do do_group_exit(),
  	 * but BUG() actually hooks all the lock-breaking and per-arch
  	 * Oops code, so that is used here instead.
  	 */
  	BUG();
  }
  
  /* Returns true if any portion of [ptr,ptr+n) over laps with [low,high). */
  static bool overlaps(const void *ptr, unsigned long n, unsigned long low,
  		     unsigned long high)
  {
  	unsigned long check_low = (uintptr_t)ptr;
  	unsigned long check_high = check_low + n;
  
  	/* Does not overlap if entirely above or entirely below. */

  	if (check_low >= high || check_high <= low)

  		return false;
  
  	return true;
  }
  
  /* Is this address range in the kernel text area? */
  static inline const char *check_kernel_text_object(const void *ptr,
  						   unsigned long n)
  {
  	unsigned long textlow = (unsigned long)_stext;
  	unsigned long texthigh = (unsigned long)_etext;
  	unsigned long textlow_linear, texthigh_linear;
  
  	if (overlaps(ptr, n, textlow, texthigh))
  		return "<kernel text>";
  
  	/*
  	 * Some architectures have virtual memory mappings with a secondary
  	 * mapping of the kernel text, i.e. there is more than one virtual
  	 * kernel address that points to the kernel image. It is usually
  	 * when there is a separate linear physical memory mapping, in that
  	 * __pa() is not just the reverse of __va(). This can be detected
  	 * and checked:
  	 */
  	textlow_linear = (unsigned long)__va(__pa(textlow));
  	/* No different mapping: we're done. */
  	if (textlow_linear == textlow)
  		return NULL;
  
  	/* Check the secondary mapping... */
  	texthigh_linear = (unsigned long)__va(__pa(texthigh));
  	if (overlaps(ptr, n, textlow_linear, texthigh_linear))
  		return "<linear kernel text>";
  
  	return NULL;
  }
  
  static inline const char *check_bogus_address(const void *ptr, unsigned long n)
  {
  	/* Reject if object wraps past end of memory. */

  	if ((unsigned long)ptr + n < (unsigned long)ptr)

  		return "<wrapped address>";
  
  	/* Reject if NULL or ZERO-allocation. */
  	if (ZERO_OR_NULL_PTR(ptr))
  		return "<null>";
  
  	return NULL;
  }

  /* Checks for allocs that are marked in some way as spanning multiple pages. */
  static inline const char *check_page_span(const void *ptr, unsigned long n,
  					  struct page *page, bool to_user)

  {

  #ifdef CONFIG_HARDENED_USERCOPY_PAGESPAN

  	const void *end = ptr + n - 1;

  	struct page *endpage;

  	bool is_reserved, is_cma;
  
  	/*

  	 * Sometimes the kernel data regions are not marked Reserved (see
  	 * check below). And sometimes [_sdata,_edata) does not cover
  	 * rodata and/or bss, so check each range explicitly.
  	 */
  
  	/* Allow reads of kernel rodata region (if not marked as Reserved). */
  	if (ptr >= (const void *)__start_rodata &&
  	    end <= (const void *)__end_rodata) {
  		if (!to_user)
  			return "<rodata>";
  		return NULL;
  	}
  
  	/* Allow kernel data region (if not marked as Reserved). */
  	if (ptr >= (const void *)_sdata && end <= (const void *)_edata)
  		return NULL;
  
  	/* Allow kernel bss region (if not marked as Reserved). */
  	if (ptr >= (const void *)__bss_start &&
  	    end <= (const void *)__bss_stop)
  		return NULL;
  
  	/* Is the object wholly within one base page? */
  	if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) ==
  		   ((unsigned long)end & (unsigned long)PAGE_MASK)))
  		return NULL;

  	/* Allow if fully inside the same compound (__GFP_COMP) page. */

  	endpage = virt_to_head_page(end);
  	if (likely(endpage == page))
  		return NULL;
  
  	/*
  	 * Reject if range is entirely either Reserved (i.e. special or
  	 * device memory), or CMA. Otherwise, reject since the object spans
  	 * several independently allocated pages.
  	 */
  	is_reserved = PageReserved(page);
  	is_cma = is_migrate_cma_page(page);
  	if (!is_reserved && !is_cma)

  		return "<spans multiple pages>";

  
  	for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
  		page = virt_to_head_page(ptr);
  		if (is_reserved && !PageReserved(page))

  			return "<spans Reserved and non-Reserved pages>";

  		if (is_cma && !is_migrate_cma_page(page))

  			return "<spans CMA and non-CMA pages>";

  	}

  #endif

  
  	return NULL;

  }
  
  static inline const char *check_heap_object(const void *ptr, unsigned long n,
  					    bool to_user)
  {
  	struct page *page;
  
  	/*
  	 * Some architectures (arm64) return true for virt_addr_valid() on
  	 * vmalloced addresses. Work around this by checking for vmalloc
  	 * first.

  	 *
  	 * We also need to check for module addresses explicitly since we
  	 * may copy static data from modules to userspace

  	 */

  	if (is_vmalloc_or_module_addr(ptr))

  		return NULL;
  
  	if (!virt_addr_valid(ptr))
  		return NULL;
  
  	page = virt_to_head_page(ptr);
  
  	/* Check slab allocator for flags and size. */
  	if (PageSlab(page))
  		return __check_heap_object(ptr, n, page);

  	/* Verify object does not incorrectly span multiple pages. */
  	return check_page_span(ptr, n, page, to_user);

  }
  
  /*
   * Validates that the given object is:
   * - not bogus address
   * - known-safe heap or stack object
   * - not in kernel text
   */
  void __check_object_size(const void *ptr, unsigned long n, bool to_user)
  {
  	const char *err;
  
  	/* Skip all tests if size is zero. */
  	if (!n)
  		return;
  
  	/* Check for invalid addresses. */
  	err = check_bogus_address(ptr, n);
  	if (err)
  		goto report;
  
  	/* Check for bad heap object. */
  	err = check_heap_object(ptr, n, to_user);
  	if (err)
  		goto report;
  
  	/* Check for bad stack object. */
  	switch (check_stack_object(ptr, n)) {
  	case NOT_STACK:
  		/* Object is not touching the current process stack. */
  		break;
  	case GOOD_FRAME:
  	case GOOD_STACK:
  		/*
  		 * Object is either in the correct frame (when it
  		 * is possible to check) or just generally on the
  		 * process stack (when frame checking not available).
  		 */
  		return;
  	default:
  		err = "<process stack>";
  		goto report;
  	}
  
  	/* Check for object in kernel to avoid text exposure. */
  	err = check_kernel_text_object(ptr, n);
  	if (!err)
  		return;
  
  report:
  	report_usercopy(ptr, n, to_user, err);
  }
  EXPORT_SYMBOL(__check_object_size);