path: root/drivers/char/mem.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/drivers/char/mem.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  Added devfs support.
 *    Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>
 *  Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>
 */

#include <linux/mm.h>
#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mman.h>
#include <linux/random.h>
#include <linux/init.h>
#include <linux/raw.h>
#include <linux/tty.h>
#include <linux/capability.h>
#include <linux/ptrace.h>
#include <linux/device.h>
#include <linux/highmem.h>
#include <linux/backing-dev.h>
#include <linux/shmem_fs.h>
#include <linux/splice.h>
#include <linux/pfn.h>
#include <linux/export.h>
#include <linux/io.h>
#include <linux/uio.h>
#include <linux/uaccess.h>
#include <linux/security.h>
#include <linux/pseudo_fs.h>
#include <uapi/linux/magic.h>
#include <linux/mount.h>

#ifdef CONFIG_IA64
# include <linux/efi.h>
#endif

#define DEVMEM_MINOR	1
#define DEVPORT_MINOR	4

static inline unsigned long size_inside_page(unsigned long start,
					     unsigned long size)
{
	unsigned long sz;

	sz = PAGE_SIZE - (start & (PAGE_SIZE - 1));

	return min(sz, size);
}

#ifndef ARCH_HAS_VALID_PHYS_ADDR_RANGE
static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)
{
	return addr + count <= __pa(high_memory);
}

static inline int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
{
	return 1;
}
#endif

#ifdef CONFIG_STRICT_DEVMEM
static inline int page_is_allowed(unsigned long pfn)
{
	return devmem_is_allowed(pfn);
}
static inline int range_is_allowed(unsigned long pfn, unsigned long size)
{
	u64 from = ((u64)pfn) << PAGE_SHIFT;
	u64 to = from + size;
	u64 cursor = from;

	while (cursor < to) {
		if (!devmem_is_allowed(pfn))
			return 0;
		cursor += PAGE_SIZE;
		pfn++;
	}
	return 1;
}
#else
static inline int page_is_allowed(unsigned long pfn)
{
	return 1;
}
static inline int range_is_allowed(unsigned long pfn, unsigned long size)
{
	return 1;
}
#endif

#ifndef unxlate_dev_mem_ptr
#define unxlate_dev_mem_ptr unxlate_dev_mem_ptr
void __weak unxlate_dev_mem_ptr(phys_addr_t phys, void *addr)
{
}
#endif

static inline bool should_stop_iteration(void)
{
	if (need_resched())
		cond_resched();
	return fatal_signal_pending(current);
}

/*
 * This funcion reads the *physical* memory. The f_pos points directly to the
 * memory location.
 */
static ssize_t read_mem(struct file *file, char __user *buf,
			size_t count, loff_t *ppos)
{
	phys_addr_t p = *ppos;
	ssize_t read, sz;
	void *ptr;
	char *bounce;
	int err;

	if (p != *ppos)
		return 0;

	if (!valid_phys_addr_range(p, count))
		return -EFAULT;
	read = 0;
#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
	/* we don't have page 0 mapped on sparc and m68k.. */
	if (p < PAGE_SIZE) {
		sz = size_inside_page(p, count);
		if (sz > 0) {
			if (clear_user(buf, sz))
				return -EFAULT;
			buf += sz;
			p += sz;
			count -= sz;
			read += sz;
		}
	}
#endif

	bounce = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!bounce)
		return -ENOMEM;

	while (count > 0) {
		unsigned long remaining;
		int allowed, probe;

		sz = size_inside_page(p, count);

		err = -EPERM;
		allowed = page_is_allowed(p >> PAGE_SHIFT);
		if (!allowed)
			goto failed;

		err = -EFAULT;
		if (allowed == 2) {
			/* Show zeros for restricted memory. */
			remaining = clear_user(buf, sz);
		} else {
			/*
			 * On ia64 if a page has been mapped somewhere as
			 * uncached, then it must also be accessed uncached
			 * by the kernel or data corruption may occur.
			 */
			ptr = xlate_dev_mem_ptr(p);
			if (!ptr)
				goto failed;

			probe = copy_from_kernel_nofault(bounce, ptr, sz);
			unxlate_dev_mem_ptr(p, ptr);
			if (probe)
				goto failed;

			remaining = copy_to_user(buf, bounce, sz);
		}

		if (remaining)
			goto failed;

		buf += sz;
		p += sz;
		count -= sz;
		read += sz;
		if (should_stop_iteration())
			break;
	}
	kfree(bounce);

	*ppos += read;
	return read;

failed:
	kfree(bounce);
	return err;
}

static ssize_t write_mem(struct file *file, const char __user *