// 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 <[email protected]>
* Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <[email protected]>
*/
#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/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>
#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
static inline bool should_stop_iteration(void)
{
if (need_resched())
cond_resched();
return 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 *buf,
size_t count, loff_t *ppos)
{
phys_addr_t p = *ppos;
ssize_t written, sz;
unsigned long copied;
void *ptr;
if (p != *ppos)
return -EFBIG;
if (!valid_phys_addr_range(p, count))
return -EFAULT;
written = 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);
/* Hmm. Do something? */
buf += sz;
p += sz;
count -= sz;
written += sz;
}
#endif
while (count > 0) {
int allowed;
sz = size_inside_page(p, count);
allowed = page_is_allowed(p >> PAGE_SHIFT);
if (!allowed)
return -EPERM;
/* Skip actual writing when a page is marked as restricted. */
if (allowed == 1) {
/*
* 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) {
if (written)
break;
return -EFAULT;
}
copied = copy_from_user(ptr, buf, sz);
unxlate_dev_mem_ptr(p, ptr);
if (copied) {
written += sz - copied;
if (written)
break;
return -EFAULT;
}
}
buf += sz;
p += sz;
count -= sz;
written += sz;
if (should_stop_iteration())
break;
}
*ppos += written;
return written;
}
int __weak phys_mem_access_prot_allowed(struct file *file,
unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
{
return 1;
}
#ifndef __HAVE_PHYS_MEM_ACCESS_PROT
/*
* Architectures vary in how they handle caching for addresses
* outside of main memory.
*
*/
#ifdef pgprot_noncached
static int uncached_access(struct file *file, phys_addr_t addr)
{
/*
* Accessing memory above the top the kernel knows about or through a
* file pointer
* that was marked O_DSYNC will be done non-cached.
*/
if (file->f_flags & O_DSYNC)
return 1;
return addr >= __pa(high_memory);
}
#endif
static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
unsigned long size, pgprot_t vma_prot)
{
#ifdef pgprot_noncached
phys_addr_t offset = pfn << PAGE_SHIFT;
if (uncached_access(file, offset))
return pgprot_noncached(vma_prot);
#endif
return vma_prot;
}
#endif
#ifndef CONFIG_MMU
static unsigned long get_unmapped_area_mem(struct file *file,
unsigned long addr,
unsigned long len,
unsigned long pgoff,
unsigned long flags)
{
if (!valid_mmap_phys_addr_range(pgoff, len))
return (unsigned long) -EINVAL;
return pgoff << PAGE_SHIFT;
}
/* permit direct mmap, for read, write or exec */
static unsigned memory_mmap_capabilities(struct file *file)
{
return NOMMU_MAP_DIRECT |
NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
}
static unsigned zero_mmap_capabilities(struct file *file)
{
return NOMMU_MAP_COPY;
}
/* can't do an in-place private mapping if there's no MMU */
static inline int private_mapping_ok(struct vm_area_struct *vma)
{
return is_nommu_shared_mapping(vma->vm_flags);
}
#else
static inline int private_mapping_ok(struct vm_area_struct *vma)
{
return 1;
}
#endif
static const struct vm_operations_struct mmap_mem_ops = {
#ifdef CONFIG_HAVE_IOREMAP_PROT
.access = generic_access_phys
#endif
};
static int mmap_mem(struct file *file, struct vm_area_struct *vma)
{
size_t size = vma->vm_end - vma->vm_start;
phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
/* Does it even fit in phys_addr_t? */
if (offset >> PAGE_SHIFT != vma->vm_pgoff)
return -EINVAL;
/* It's illegal to wrap around the end of the physical address space. */
if (offset + (phys_addr_t)size - 1 < offset)
return -EINVAL;
if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
return -EINVAL;
if (!private_mapping_ok(vma))
return -ENOSYS;
if (!range_is_allowed(vma->vm_pgoff, size))
return -EPERM;
if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
&vma->vm_page_prot))
return -EINVAL;
vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
size,
vma->vm_page_prot);
vma->vm_ops = &mmap_mem_ops;
/* Remap-pfn-range will mark the range VM_IO */
if (remap_pfn_range(vma,
vma->vm_start,
vma->vm_pgoff,
size,
vma->vm_page_prot)) {
return -EAGAIN;
}
return 0;
}
#ifdef CONFIG_DEVPORT
static ssize_t read_port(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
unsigned long i = *ppos;
char __user *tmp = buf;
if (!access_ok(buf, count))
return -EFAULT;
while (count-- > 0 && i < 65536) {
if (__put_user(inb(i), tmp) < 0)
return -EFAULT;
i++;
tmp++;
}
*ppos = i;
return tmp-buf;
}
static ssize_t write_port(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
unsigned long i = *ppos;
const char __user *tmp = buf;
if (!access_ok(buf, count))
return -EFAULT;
while (count-- > 0 && i < 65536) {
char c;
if (__get_user(c, tmp)) {
if (tmp > buf)
break;
return -EFAULT;
}
outb(c, i);
i++;
tmp++;
}
*ppos = i;
return tmp-buf;
}
#endif
static ssize_t read_null(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
return 0;
}
static ssize_t write_null(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
return count;
}
static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
{
return 0;
}
static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
{
size_t count = iov_iter_count(from);
iov_iter_advance(from, count);
return count;
}
static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
struct splice_desc *sd)
{
return sd->len;
}
static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
loff_t *ppos, size_t len, unsigned int flags)
{
return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_null);
}
static int uring_cmd_null(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
{
return 0;
}
static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
{
size_t written = 0;
while (iov_iter_count(iter)) {
size_t chunk = iov_iter_count(iter), n;
if (chunk > PAGE_SIZE)
chunk = PAGE_SIZE; /* Just for latency reasons */
n = iov_iter_zero(chunk, iter);
if (!n && iov_iter_count(iter))
return written ? written : -EFAULT;
written += n;
if (signal_pending(current))
return written ? written : -ERESTARTSYS;
if (!need_resched())
continue;
if (iocb->ki_flags & IOCB_NOWAIT)
return written ? written : -EAGAIN;
cond_resched();
}
return written;
}
static ssize_t read_zero(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
size_t cleared = 0;
while (count) {
size_t chunk = min_t(size_t, count, PAGE_SIZE);
size_t left;
left = clear_user(buf + cleared, chunk);
if (unlikely(left)) {
cleared += (chunk - left);
if (!cleared)
return -EFAULT;
break;
}
cleared += chunk;
count -= chunk;
if (signal_pending(current))
break;
cond_resched();
}
return cleared;
}
static int mmap_zero(struct file *file, struct vm_area_struct *vma)
{
#ifndef CONFIG_MMU
return -ENOSYS;
#endif
if (vma->vm_flags & VM_SHARED)
return shmem_zero_setup(vma);
vma_set_anonymous(vma);
return 0;
}
static unsigned long get_unmapped_area_zero(struct file *file,
unsigned long addr, unsigned long len,
unsigned long pgoff, unsigned long flags)
{
#ifdef CONFIG_MMU
if (flags & MAP_SHARED) {
/*
* mmap_zero() will call shmem_zero_setup() to create a file,
* so use shmem's get_unmapped_area in case it can be huge;
* and pass NULL for file as in mmap.c's get_unmapped_area(),
* so as not to confuse shmem with our handle on "/dev/zero".
*/
return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
}
/* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags);
#else
return -ENOSYS;
#endif
}
static ssize_t write_full(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
return -ENOSPC;
}
/*
* Special lseek() function for /dev/null and /dev/zero. Most notably, you
* can fopen() both devices with "a" now. This was previously impossible.
* -- SRB.
*/
static loff_t null_lseek(struct file *file, loff_t offset, int orig)
{
return file->f_pos = 0;
}
/*
* The memory devices use the full 32/64 bits of the offset, and so we cannot
* check against negative addresses: they are ok. The return value is weird,
* though, in that case (0).
*
* also note that seeking relative to the "end of file" isn't supported:
* it has no meaning, so it returns -EINVAL.
*/
static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
{
loff_t ret;
inode_lock(file_inode(file));
switch (orig) {
case SEEK_CUR:
offset += file->f_pos;
fallthrough;
case SEEK_SET:
/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
if ((unsigned long long)offset >= -MAX_ERRNO) {
ret = -EOVERFLOW;
break;
}
file->f_pos = offset;
ret = file->f_pos;
force_successful_syscall_return();
break;
default:
ret = -EINVAL;
}
inode_unlock(file_inode(file));
return ret;
}
static int open_port(struct inode *inode, struct file *filp)
{
int rc;
if (!capable(CAP_SYS_RAWIO))
return -EPERM;
rc = security_locked_down(LOCKDOWN_DEV_MEM);
if (rc)
return rc;
if (iminor(inode) != DEVMEM_MINOR)
return 0;
/*
* Use a unified address space to have a single point to manage
* revocations when drivers want to take over a /dev/mem mapped
* range.
*/
filp->f_mapping = iomem_get_mapping();
return 0;
}
#define zero_lseek null_lseek
#define full_lseek null_lseek
#define write_zero write_null
#define write_iter_zero write_iter_null
#define splice_write_zero splice_write_null
#define open_mem open_port
static const struct file_operations __maybe_unused mem_fops = {
.llseek = memory_lseek,
.read = read_mem,
.write = write_mem,
.mmap = mmap_mem,
.open = open_mem,
#ifndef CONFIG_MMU
.get_unmapped_area = get_unmapped_area_mem,
.mmap_capabilities = memory_mmap_capabilities,
#endif
.fop_flags = FOP_UNSIGNED_OFFSET,
};
static const struct file_operations null_fops = {
.llseek = null_lseek,
.read = read_null,
.write = write_null,
.read_iter = read_iter_null,
.write_iter = write_iter_null,
.splice_write = splice_write_null,
.uring_cmd = uring_cmd_null,
};
#ifdef CONFIG_DEVPORT
static const struct file_operations port_fops = {
.llseek = memory_lseek,
.read = read_port,
.write = write_port,
.open = open_port,
};
#endif
static const struct file_operations zero_fops = {
.llseek = zero_lseek,
.write = write_zero,
.read_iter = read_iter_zero,
.read = read_zero,
.write_iter = write_iter_zero,
.splice_read = copy_splice_read,
.splice_write = splice_write_zero,
.mmap = mmap_zero,
.get_unmapped_area = get_unmapped_area_zero,
#ifndef CONFIG_MMU
.mmap_capabilities = zero_mmap_capabilities,
#endif
};
static const struct file_operations full_fops = {
.llseek = full_lseek,
.read_iter = read_iter_zero,
.write = write_full,
.splice_read = copy_splice_read,
};
static const struct memdev {
const char *name;
const struct file_operations *fops;
fmode_t fmode;
umode_t mode;
} devlist[] = {
#ifdef CONFIG_DEVMEM
[DEVMEM_MINOR] = { "mem", &mem_fops, 0, 0 },
#endif
[3] = { "null", &null_fops, FMODE_NOWAIT, 0666 },
#ifdef CONFIG_DEVPORT
[4] = { "port", &port_fops, 0, 0 },
#endif
[5] = { "zero", &zero_fops, FMODE_NOWAIT, 0666 },
[7] = { "full", &full_fops, 0, 0666 },
[8] = { "random", &random_fops, FMODE_NOWAIT, 0666 },
[9] = { "urandom", &urandom_fops, FMODE_NOWAIT, 0666 },
#ifdef CONFIG_PRINTK
[11] = { "kmsg", &kmsg_fops, 0, 0644 },
#endif
};
static int memory_open(struct inode *inode, struct file *filp)
{
int minor;
const struct memdev *dev;
minor = iminor(inode);
if (minor >= ARRAY_SIZE(devlist))
return -ENXIO;
dev = &devlist[minor];
if (!dev->fops)
return -ENXIO;
filp->f_op = dev->fops;
filp->f_mode |= dev->fmode;
if (dev->fops->open)
return dev->fops->open(inode, filp);
return 0;
}
static const struct file_operations memory_fops = {
.open = memory_open,
.llseek = noop_llseek,
};
static char *mem_devnode(const struct device *dev, umode_t *mode)
{
if (mode && devlist[MINOR(dev->devt)].mode)
*mode = devlist[MINOR(dev->devt)].mode;
return NULL;
}
static const struct class mem_class = {
.name = "mem",
.devnode = mem_devnode,
};
static int __init chr_dev_init(void)
{
int retval;
int minor;
if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
printk("unable to get major %d for memory devs\n", MEM_MAJOR);
retval = class_register(&mem_class);
if (retval)
return retval;
for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
if (!devlist[minor].name)
continue;
/*
* Create /dev/port?
*/
if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
continue;
device_create(&mem_class, NULL, MKDEV(MEM_MAJOR, minor),
NULL, devlist[minor].name);
}
return tty_init();
}
fs_initcall(chr_dev_init);
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