/*
 * 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)\n",
		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);
to the i915 developers on Jan 8, applying the
  ugly workaround on my own now after triggering the problem for the
  second time with no feedback.

  This is likely to be the same bug reported as

     https://bugs.freedesktop.org/show_bug.cgi?id=98829
     https://bugs.freedesktop.org/show_bug.cgi?id=99134

  which has a patch for the underlying problem, but it hasn't gotten to
  me, so I'm applying the workaround. ]

Cc: Daniel Vetter &lt;daniel.vetter@intel.com&gt;
Cc: Jani Nikula &lt;jani.nikula@linux.intel.com&gt;
Cc: Ville Syrjälä &lt;ville.syrjala@linux.intel.com&gt;
Cc: Chris Wilson &lt;chris@chris-wilson.co.uk&gt;
Cc: Maarten Lankhorst &lt;maarten.lankhorst@linux.intel.com&gt;
Cc: Tvrtko Ursulin &lt;tvrtko.ursulin@intel.com&gt;
Cc: Imre Deak &lt;imre.deak@intel.com&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=39cb2c9a316e77f6dfba96c543e55b6672d5a37e'>Diffstat</a> (limited to 'include/uapi/sound/asound_fm.h')</div><table summary='diffstat' class='diffstat'>