// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * linux/mm/process_vm_access.c
 *
 * Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@au1.ibm.com>, IBM Corp.
 */

#include <linux/compat.h>
#include <linux/mm.h>
#include <linux/uio.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/highmem.h>
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/syscalls.h>

/**
 * process_vm_rw_pages - read/write pages from task specified
 * @pages: array of pointers to pages we want to copy
 * @offset: offset in page to start copying from/to
 * @len: number of bytes to copy
 * @iter: where to copy to/from locally
 * @vm_write: 0 means copy from, 1 means copy to
 * Returns 0 on success, error code otherwise
 */
static int process_vm_rw_pages(struct page **pages,
                               unsigned offset,
                               size_t len,
                               struct iov_iter *iter,
                               int vm_write)
{
        /* Do the copy for each page */
        while (len && iov_iter_count(iter)) {
                struct page *page = *pages++;
                size_t copy = PAGE_SIZE - offset;
                size_t copied;

                if (copy > len)
                        copy = len;

                if (vm_write)
                        copied = copy_page_from_iter(page, offset, copy, iter);
                else
                        copied = copy_page_to_iter(page, offset, copy, iter);

                len -= copied;
                if (copied < copy && iov_iter_count(iter))
                        return -EFAULT;
                offset = 0;
        }
        return 0;
}

/* Maximum number of pages kmalloc'd to hold struct page's during copy */
#define PVM_MAX_KMALLOC_PAGES 2

/* Maximum number of pages that can be stored at a time */
#define PVM_MAX_USER_PAGES (PVM_MAX_KMALLOC_PAGES * PAGE_SIZE / sizeof(struct page *))

/**
 * process_vm_rw_single_vec - read/write pages from task specified
 * @addr: start memory address of target process
 * @len: size of area to copy to/from
 * @iter: where to copy to/from locally
 * @process_pages: struct pages area that can store at least
 *  nr_pages_to_copy struct page pointers
 * @mm: mm for task
 * @task: task to read/write from
 * @vm_write: 0 means copy from, 1 means copy to
 * Returns 0 on success or on failure error code
 */
static int process_vm_rw_single_vec(unsigned long addr,
                                    unsigned long len,
                                    struct iov_iter *iter,
                                    struct page **process_pages,
                                    struct mm_struct *mm,
                                    struct task_struct *task,
                                    int vm_write)
{
        unsigned long pa = addr & PAGE_MASK;
        unsigned long start_offset = addr - pa;
        unsigned long nr_pages;
        ssize_t rc = 0;
        unsigned int flags = 0;

        /* Work out address and page range required */
        if (len == 0)
                return 0;
        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;

        if (vm_write)
                flags |= FOLL_WRITE;

        while (!rc && nr_pages && iov_iter_count(iter)) {
                int pinned_pages = min_t(unsigned long, nr_pages, PVM_MAX_USER_PAGES);
                int locked = 1;
                size_t bytes;

                /*
                 * Get the pages we're interested in.  We must
                 * access remotely because task/mm might not
                 * current/current->mm
                 */
                mmap_read_lock(mm);
                pinned_pages = pin_user_pages_remote(mm, pa, pinned_pages,
                                                     flags, process_pages,
                                                     &locked);
                if (locked)
                        mmap_read_unlock(mm);
                if (pinned_pages <= 0)
                        return -EFAULT;

                bytes = pinned_pages * PAGE_SIZE - start_offset;
                if (bytes > len)
                        bytes = len;

                rc = process_vm_rw_pages(process_pages,
                                         start_offset, bytes, iter,
                                         vm_write);
                len -= bytes;
                start_offset = 0;
                nr_pages -= pinned_pages;
                pa += pinned_pages * PAGE_SIZE;

                /* If vm_write is set, the pages need to be made dirty: */
                unpin_user_pages_dirty_lock(process_pages, pinned_pages,
                                            vm_write);
        }

        return rc;
}

/* Maximum number of entries for process pages array
   which lives on stack */
#define PVM_MAX_PP_ARRAY_COUNT 16

/**
 * process_vm_rw_core - core of reading/writing pages from task specified
 * @pid: PID of process to read/write from/to
 * @iter: where to copy to/from locally
 * @rvec: iovec array specifying where to copy to/from in the other process
 * @riovcnt: size of rvec array
 * @flags: currently unused
 * @vm_write: 0 if reading from other process, 1 if writing to other process
 *
 * Returns the number of bytes read/written or error code. May
 *  return less bytes than expected if an error occurs during the copying
 *  process.
 */
static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
                                  const struct iovec *rvec,
                                  unsigned long riovcnt,
                                  unsigned long flags, int vm_write)
{
        struct task_struct *task;
        struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
        struct page **process_pages = pp_stack;
        struct mm_struct *mm;
        unsigned long i;
        ssize_t rc = 0;
        unsigned long nr_pages = 0;
        unsigned long nr_pages_iov;
        ssize_t iov_len;
        size_t total_len = iov_iter_count(iter);

        /*
         * Work out how many pages of struct pages we're going to need
         * when eventually calling get_user_pages
         */
        for (i = 0; i < riovcnt; i++) {
                iov_len = rvec[i].iov_len;
                if (iov_len > 0) {
                        nr_pages_iov = ((unsigned long)rvec[i].iov_base
                                        + iov_len - 1)
                                / PAGE_SIZE - (unsigned long)rvec[i].iov_base
                                / PAGE_SIZE + 1;
                        nr_pages = max(nr_pages, nr_pages_iov);
                }
        }

        if (nr_pages == 0)
                return 0;

        if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
                /* For reliability don't try to kmalloc more than
                   2 pages worth */
                process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES * PAGE_SIZE,
                                              sizeof(struct page *)*nr_pages),
                                        GFP_KERNEL);

                if (!process_pages)
                        return -ENOMEM;
        }

        /* Get process information */
        task = find_get_task_by_vpid(pid);
        if (!task) {
                rc = -ESRCH;
                goto free_proc_pages;
        }

        mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
        if (IS_ERR(mm)) {
                rc = PTR_ERR(mm);
                /*
                 * Explicitly map EACCES to EPERM as EPERM is a more
                 * appropriate error code for process_vw_readv/writev
                 */
                if (rc == -EACCES)
                        rc = -EPERM;
                goto put_task_struct;
        }

        for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
                rc = process_vm_rw_single_vec(
                        (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
                        iter, process_pages, mm, task, vm_write);

        /* copied = space before - space after */
        total_len -= iov_iter_count(iter);

        /* If we have managed to copy any data at all then
           we return the number of bytes copied. Otherwise
           we return the error code */
        if (total_len)
                rc = total_len;

        mmput(mm);

put_task_struct:
        put_task_struct(task);

free_proc_pages:
        if (process_pages != pp_stack)
                kfree(process_pages);
        return rc;
}

/**
 * process_vm_rw - check iovecs before calling core routine
 * @pid: PID of process to read/write from/to
 * @lvec: iovec array specifying where to copy to/from locally
 * @liovcnt: size of lvec array
 * @rvec: iovec array specifying where to copy to/from in the other process
 * @riovcnt: size of rvec array
 * @flags: currently unused
 * @vm_write: 0 if reading from other process, 1 if writing to other process
 *
 * Returns the number of bytes read/written or error code. May
 *  return less bytes than expected if an error occurs during the copying
 *  process.
 */
static ssize_t process_vm_rw(pid_t pid,
                             const struct iovec __user *lvec,
                             unsigned long liovcnt,
                             const struct iovec __user *rvec,
                             unsigned long riovcnt,
                             unsigned long flags, int vm_write)
{
        struct iovec iovstack_l[UIO_FASTIOV];
        struct iovec iovstack_r[UIO_FASTIOV];
        struct iovec *iov_l = iovstack_l;
        struct iovec *iov_r;
        struct iov_iter iter;
        ssize_t rc;
        int dir = vm_write ? ITER_SOURCE : ITER_DEST;

        if (flags != 0)
                return -EINVAL;

        /* Check iovecs */
        rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
        if (rc < 0)
                return rc;
        if (!iov_iter_count(&iter))
                goto free_iov_l;
        iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r,
                                in_compat_syscall());
        if (IS_ERR(iov_r)) {
                rc = PTR_ERR(iov_r);
                goto free_iov_l;
        }
        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
        if (iov_r != iovstack_r)
                kfree(iov_r);
free_iov_l:
        kfree(iov_l);
        return rc;
}

SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
                unsigned long, liovcnt, const struct iovec __user *, rvec,
                unsigned long, riovcnt, unsigned long, flags)
{
        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
}

SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
                const struct iovec __user *, lvec,
                unsigned long, liovcnt, const struct iovec __user *, rvec,
                unsigned long, riovcnt, unsigned long, flags)
{
        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
}