Quelle process_vm_access.c Sprache: C

// 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);
}

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