// 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/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);
}
#else
static inline int page_is_allowed(unsigned long pfn)
{
        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_desc *desc)
{
        return is_nommu_shared_vma_flags(&desc->vma_flags);
}
#else

static inline int private_mapping_ok(struct vm_area_desc *desc)
{
        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_filter_error(int err)
{
        return -EAGAIN;
}

static int mmap_mem_prepare(struct vm_area_desc *desc)
{
        struct file *file = desc->file;
        const size_t size = vma_desc_size(desc);
        const phys_addr_t offset = (phys_addr_t)desc->pgoff << PAGE_SHIFT;

        /* Does it even fit in phys_addr_t? */
        if (offset >> PAGE_SHIFT != desc->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(desc->pgoff, size))
                return -EINVAL;

        if (!private_mapping_ok(desc))
                return -ENOSYS;

        if (!range_is_allowed(desc->pgoff, size))
                return -EPERM;

        if (!phys_mem_access_prot_allowed(file, desc->pgoff, size,
                                          &desc->page_prot))
                return -EINVAL;

        desc->page_prot = phys_mem_access_prot(file, desc->pgoff,
                                               size,
                                               desc->page_prot);

        desc->vm_ops = &mmap_mem_ops;

        /* Remap-pfn-range will mark the range with the I/O flag. */
        mmap_action_remap_full(desc, desc->pgoff);
        /* We filter remap errors to -EAGAIN. */
        desc->action.error_hook = mmap_filter_error;

        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_private_success(const struct vm_area_struct *vma)
{
        /*
         * This is a highly unique situation where we mark a MAP_PRIVATE mapping
         * of /dev/zero anonymous, despite it not being.
         */
        vma_set_anonymous((struct vm_area_struct *)vma);

        return 0;
}

static int mmap_zero_prepare(struct vm_area_desc *desc)
{
#ifndef CONFIG_MMU
        return -ENOSYS;
#endif
        if (vma_desc_test_flags(desc, VMA_SHARED_BIT))
                return shmem_zero_setup_desc(desc);

        desc->action.success_hook = mmap_zero_private_success;
        return 0;
}

#ifndef CONFIG_MMU
static unsigned long get_unmapped_area_zero(struct file *file,
                                unsigned long addr, unsigned long len,
                                unsigned long pgoff, unsigned long flags)
{
        return -ENOSYS;
}
#else
static unsigned long get_unmapped_area_zero(struct file *file,
                                unsigned long addr, unsigned long len,
                                unsigned long pgoff, unsigned long flags)
{
        if (flags & MAP_SHARED) {
                /*
                 * mmap_zero_prepare() 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,
         * attempt to map aligned to huge page size if possible, otherwise we
         * fall back to system page size mappings.
         */
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        return thp_get_unmapped_area(file, addr, len, pgoff, flags);
#else
        return mm_get_unmapped_area(file, addr, len, pgoff, flags);
#endif
}
#endif /* CONFIG_MMU */

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_prepare   = mmap_mem_prepare,
        .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_prepare   = mmap_zero_prepare,
        .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);