linux/mm/usercopy.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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.
 */
#define pr_fmt(fmt) …

#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/kstrtox.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/vmalloc.h>
#include <linux/atomic.h>
#include <linux/jump_label.h>
#include <asm/sections.h>
#include "slab.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: within the current stack (when can't frame-check exactly)
 *	BAD_STACK: error condition (invalid stack position or bad stack frame)
 */
static noinline int check_stack_object(const void *obj, unsigned long len)
{ … }

/*
 * 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 __noreturn usercopy_abort(const char *name, const char *detail,
			       bool to_user, unsigned long offset,
			       unsigned long len)
{ … }

/* 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)
{ … }

/* 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)
{ … }

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

static inline void check_heap_object(const void *ptr, unsigned long n,
				     bool 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)
{ … }
EXPORT_SYMBOL(…);

static bool enable_checks __initdata = …;

static int __init parse_hardened_usercopy(char *str)
{ … }

__setup(…);

static int __init set_hardened_usercopy(void)
{ … }

late_initcall(set_hardened_usercopy);