/*
   * 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 <linux/sched.h>

  #include <linux/sched/task.h>
  #include <linux/sched/task_stack.h>

  #include <linux/thread_info.h>

  #include <linux/atomic.h>
  #include <linux/jump_label.h>

  #include <asm/sections.h>

  /*
   * 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;
  }

  /*

   * If these functions are reached, then CONFIG_HARDENED_USERCOPY has found
   * an unexpected state during a copy_from_user() or copy_to_user() call.

   * There are several checks being performed on the buffer by the
   * __check_object_size() function. Normal stack buffer usage should never
   * trip the checks, and kernel text addressing will always trip the check.

   * For cache objects, it is checking that only the whitelisted range of
   * bytes for a given cache is being accessed (via the cache's usersize and
   * useroffset fields). To adjust a cache whitelist, use the usercopy-aware
   * kmem_cache_create_usercopy() function to create the cache (and
   * carefully audit the whitelist range).

   */

  void usercopy_warn(const char *name, const char *detail, bool to_user,
  		   unsigned long offset, unsigned long len)
  {
  	WARN_ONCE(1, "Bad or missing usercopy whitelist? Kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)!
  ",
  		 to_user ? "exposure" : "overwrite",
  		 to_user ? "from" : "to",
  		 name ? : "unknown?!",
  		 detail ? " '" : "", detail ? : "", detail ? "'" : "",
  		 offset, len);
  }

  void __noreturn usercopy_abort(const char *name, const char *detail,
  			       bool to_user, unsigned long offset,
  			       unsigned long len)

  {

  	pr_emerg("Kernel memory %s attempt detected %s %s%s%s%s (offset %lu, size %lu)!
  ",
  		 to_user ? "exposure" : "overwrite",
  		 to_user ? "from" : "to",
  		 name ? : "unknown?!",
  		 detail ? " '" : "", detail ? : "", detail ? "'" : "",
  		 offset, 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 unsigned long ptr, unsigned long n,
  		     unsigned long low, unsigned long high)

  {

  	const unsigned long check_low = 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 void check_kernel_text_object(const unsigned long ptr,
  					    unsigned long n, bool to_user)

  {
  	unsigned long textlow = (unsigned long)_stext;
  	unsigned long texthigh = (unsigned long)_etext;
  	unsigned long textlow_linear, texthigh_linear;
  
  	if (overlaps(ptr, n, textlow, texthigh))

  		usercopy_abort("kernel text", NULL, to_user, ptr - textlow, n);

  
  	/*
  	 * 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)lm_alias(textlow);

  	/* No different mapping: we're done. */
  	if (textlow_linear == textlow)

  		return;

  
  	/* Check the secondary mapping... */

  	texthigh_linear = (unsigned long)lm_alias(texthigh);

  	if (overlaps(ptr, n, textlow_linear, texthigh_linear))

  		usercopy_abort("linear kernel text", NULL, to_user,
  			       ptr - textlow_linear, n);

  }

  static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
  				       bool to_user)

  {
  	/* Reject if object wraps past end of memory. */

  	if (ptr + n < ptr)
  		usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);

  
  	/* Reject if NULL or ZERO-allocation. */
  	if (ZERO_OR_NULL_PTR(ptr))

  		usercopy_abort("null address", NULL, to_user, ptr, n);

  }

  /* Checks for allocs that are marked in some way as spanning multiple pages. */

  static inline void 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)

  			usercopy_abort("rodata", NULL, to_user, 0, n);
  		return;

  	}
  
  	/* Allow kernel data region (if not marked as Reserved). */
  	if (ptr >= (const void *)_sdata && end <= (const void *)_edata)

  		return;

  
  	/* Allow kernel bss region (if not marked as Reserved). */
  	if (ptr >= (const void *)__bss_start &&
  	    end <= (const void *)__bss_stop)

  		return;

  
  	/* 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;

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

  	endpage = virt_to_head_page(end);
  	if (likely(endpage == page))

  		return;

  
  	/*
  	 * 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)

  		usercopy_abort("spans multiple pages", NULL, to_user, 0, n);

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

  			usercopy_abort("spans Reserved and non-Reserved pages",
  				       NULL, to_user, 0, n);

  		if (is_cma && !is_migrate_cma_page(page))

  			usercopy_abort("spans CMA and non-CMA pages", NULL,
  				       to_user, 0, n);

  	}

  #endif

  }

  static inline void check_heap_object(const void *ptr, unsigned long n,
  				     bool to_user)

  {
  	struct page *page;

  	if (!virt_addr_valid(ptr))

  		return;

  
  	page = virt_to_head_page(ptr);

  	if (PageSlab(page)) {
  		/* Check slab allocator for flags and size. */
  		__check_heap_object(ptr, n, page, to_user);
  	} else {
  		/* Verify object does not incorrectly span multiple pages. */
  		check_page_span(ptr, n, page, to_user);
  	}

  }

  static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks);

  /*
   * Validates that the given object is:
   * - not bogus address

   * - fully contained by stack (or stack frame, when available)
   * - fully within SLAB object (or object whitelist area, when available)

   * - not in kernel text
   */
  void __check_object_size(const void *ptr, unsigned long n, bool to_user)
  {

  	if (static_branch_unlikely(&bypass_usercopy_checks))
  		return;

  	/* Skip all tests if size is zero. */
  	if (!n)
  		return;
  
  	/* Check for invalid addresses. */

  	check_bogus_address((const unsigned long)ptr, n, to_user);

  	/* 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:

  		usercopy_abort("process stack", NULL, to_user, 0, n);

  	}

  	/* Check for bad heap object. */
  	check_heap_object(ptr, n, to_user);

  	/* Check for object in kernel to avoid text exposure. */

  	check_kernel_text_object((const unsigned long)ptr, n, to_user);

  }
  EXPORT_SYMBOL(__check_object_size);

  
  static bool enable_checks __initdata = true;
  
  static int __init parse_hardened_usercopy(char *str)
  {
  	return strtobool(str, &enable_checks);
  }
  
  __setup("hardened_usercopy=", parse_hardened_usercopy);
  
  static int __init set_hardened_usercopy(void)
  {
  	if (enable_checks == false)
  		static_branch_enable(&bypass_usercopy_checks);
  	return 1;
  }
  
  late_initcall(set_hardened_usercopy);