Re: [PATCH] mm/process_vm_access: move into ipc/

[Konstantin Khlebnikov]

On Mon, May 26, 2014 at 11:16 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote:
> On Sat, 24 May 2014, Konstantin Khlebnikov wrote:
>
>> "CROSS_MEMORY_ATTACH" and mm/process_vm_access.c seems misnamed and misplaced.
>> Actually it's a kind of IPC and it has no more relation to MM than sys_read().
>> This patch moves code into ipc/ and config option into init/Kconfig.
>>
>> Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
>
> I disagree, and SysV's ipc/ isn't where I would expect to find it.
> How about we just leave it where it is in mm?

Ok, how about moving only config option? It adds couple syscalls and
nothing more.
I don't think it should be in "Processor type and features".
All other options related to non-standard syscalls are in "General
setup' init/Kconfig.

>
> Hugh
>
>> ---
>>  init/Kconfig            |   10 +
>>  ipc/Makefile            |    1
>>  ipc/process_vm_access.c |  383 +++++++++++++++++++++++++++++++++++++++++++++++
>>  mm/Kconfig              |   10 -
>>  mm/Makefile             |    4
>>  mm/process_vm_access.c  |  383 -----------------------------------------------
>>  6 files changed, 394 insertions(+), 397 deletions(-)
>>  create mode 100644 ipc/process_vm_access.c
>>  delete mode 100644 mm/process_vm_access.c
>>
>> diff --git a/init/Kconfig b/init/Kconfig
>> index 9d3585b..d6ddb7a 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -261,6 +261,16 @@ config POSIX_MQUEUE_SYSCTL
>>       depends on SYSCTL
>>       default y
>>
>> +config CROSS_MEMORY_ATTACH
>> +     bool "Enable process_vm_readv/writev syscalls"
>> +     depends on MMU
>> +     default y
>> +     help
>> +       Enabling this option adds the system calls process_vm_readv and
>> +       process_vm_writev which allow a process with the correct privileges
>> +       to directly read from or write to to another process's address space.
>> +       See the man page for more details.
>> +
>>  config FHANDLE
>>       bool "open by fhandle syscalls"
>>       select EXPORTFS
>> diff --git a/ipc/Makefile b/ipc/Makefile
>> index 9075e17..6982d3e 100644
>> --- a/ipc/Makefile
>> +++ b/ipc/Makefile
>> @@ -9,4 +9,5 @@ obj_mq-$(CONFIG_COMPAT) += compat_mq.o
>>  obj-$(CONFIG_POSIX_MQUEUE) += mqueue.o msgutil.o $(obj_mq-y)
>>  obj-$(CONFIG_IPC_NS) += namespace.o
>>  obj-$(CONFIG_POSIX_MQUEUE_SYSCTL) += mq_sysctl.o
>> +obj-$(CONFIG_CROSS_MEMORY_ATTACH) += process_vm_access.o
>>
>> diff --git a/ipc/process_vm_access.c b/ipc/process_vm_access.c
>> new file mode 100644
>> index 0000000..65aacea
>> --- /dev/null
>> +++ b/ipc/process_vm_access.c
>> @@ -0,0 +1,383 @@
>> +/*
>> + * linux/ipc/process_vm_access.c
>> + *
>> + * Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@xxxxxxxxxxx>, IBM Corp.
>> + *
>> + * This program is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU General Public License
>> + * as published by the Free Software Foundation; either version
>> + * 2 of the License, or (at your option) any later version.
>> + */
>> +
>> +#include <linux/mm.h>
>> +#include <linux/uio.h>
>> +#include <linux/sched.h>
>> +#include <linux/highmem.h>
>> +#include <linux/ptrace.h>
>> +#include <linux/slab.h>
>> +#include <linux/syscalls.h>
>> +
>> +#ifdef CONFIG_COMPAT
>> +#include <linux/compat.h>
>> +#endif
>> +
>> +/**
>> + * process_vm_rw_pages - read/write pages from task specified
>> + * @pages: array of pointers to pages we want to copy
>> + * @start_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) {
>> +                     if (copy > iov_iter_count(iter))
>> +                             copy = iov_iter_count(iter);
>> +                     copied = iov_iter_copy_from_user(page, iter,
>> +                                     offset, copy);
>> +                     iov_iter_advance(iter, copied);
>> +                     set_page_dirty_lock(page);
>> +             } 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 (PAGE_SIZE * 2)
>> +
>> +/**
>> + * 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 long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
>> +             / sizeof(struct pages *);
>> +
>> +     /* Work out address and page range required */
>> +     if (len == 0)
>> +             return 0;
>> +     nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
>> +
>> +     while (!rc && nr_pages && iov_iter_count(iter)) {
>> +             int pages = min(nr_pages, max_pages_per_loop);
>> +             size_t bytes;
>> +
>> +             /* Get the pages we're interested in */
>> +             down_read(&mm->mmap_sem);
>> +             pages = get_user_pages(task, mm, pa, pages,
>> +                                   vm_write, 0, process_pages, NULL);
>> +             up_read(&mm->mmap_sem);
>> +
>> +             if (pages <= 0)
>> +                     return -EFAULT;
>> +
>> +             bytes = 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 -= pages;
>> +             pa += pages * PAGE_SIZE;
>> +             while (pages)
>> +                     put_page(process_pages[--pages]);
>> +     }
>> +
>> +     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)
>> +                             / 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,
>> +                                           sizeof(struct pages *)*nr_pages),
>> +                                     GFP_KERNEL);
>> +
>> +             if (!process_pages)
>> +                     return -ENOMEM;
>> +     }
>> +
>> +     /* Get process information */
>> +     rcu_read_lock();
>> +     task = find_task_by_vpid(pid);
>> +     if (task)
>> +             get_task_struct(task);
>> +     rcu_read_unlock();
>> +     if (!task) {
>> +             rc = -ESRCH;
>> +             goto free_proc_pages;
>> +     }
>> +
>> +     mm = mm_access(task, PTRACE_MODE_ATTACH);
>> +     if (!mm || IS_ERR(mm)) {
>> +             rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
>> +             /*
>> +              * Explicitly map EACCES to EPERM as EPERM is a more a
>> +              * 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 = iovstack_r;
>> +     struct iov_iter iter;
>> +     ssize_t rc;
>> +
>> +     if (flags != 0)
>> +             return -EINVAL;
>> +
>> +     /* Check iovecs */
>> +     if (vm_write)
>> +             rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
>> +                                        iovstack_l, &iov_l);
>> +     else
>> +             rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
>> +                                        iovstack_l, &iov_l);
>> +     if (rc <= 0)
>> +             goto free_iovecs;
>> +
>> +     iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
>> +
>> +     rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
>> +                                iovstack_r, &iov_r);
>> +     if (rc <= 0)
>> +             goto free_iovecs;
>> +
>> +     rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
>> +
>> +free_iovecs:
>> +     if (iov_r != iovstack_r)
>> +             kfree(iov_r);
>> +     if (iov_l != iovstack_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);
>> +}
>> +
>> +#ifdef CONFIG_COMPAT
>> +
>> +static ssize_t
>> +compat_process_vm_rw(compat_pid_t pid,
>> +                  const struct compat_iovec __user *lvec,
>> +                  unsigned long liovcnt,
>> +                  const struct compat_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 = iovstack_r;
>> +     struct iov_iter iter;
>> +     ssize_t rc = -EFAULT;
>> +
>> +     if (flags != 0)
>> +             return -EINVAL;
>> +
>> +     if (vm_write)
>> +             rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
>> +                                               UIO_FASTIOV, iovstack_l,
>> +                                               &iov_l);
>> +     else
>> +             rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
>> +                                               UIO_FASTIOV, iovstack_l,
>> +                                               &iov_l);
>> +     if (rc <= 0)
>> +             goto free_iovecs;
>> +     iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
>> +     rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
>> +                                       UIO_FASTIOV, iovstack_r,
>> +                                       &iov_r);
>> +     if (rc <= 0)
>> +             goto free_iovecs;
>> +
>> +     rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
>> +
>> +free_iovecs:
>> +     if (iov_r != iovstack_r)
>> +             kfree(iov_r);
>> +     if (iov_l != iovstack_l)
>> +             kfree(iov_l);
>> +     return rc;
>> +}
>> +
>> +COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
>> +                    const struct compat_iovec __user *, lvec,
>> +                    compat_ulong_t, liovcnt,
>> +                    const struct compat_iovec __user *, rvec,
>> +                    compat_ulong_t, riovcnt,
>> +                    compat_ulong_t, flags)
>> +{
>> +     return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
>> +                                 riovcnt, flags, 0);
>> +}
>> +
>> +COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
>> +                    const struct compat_iovec __user *, lvec,
>> +                    compat_ulong_t, liovcnt,
>> +                    const struct compat_iovec __user *, rvec,
>> +                    compat_ulong_t, riovcnt,
>> +                    compat_ulong_t, flags)
>> +{
>> +     return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
>> +                                 riovcnt, flags, 1);
>> +}
>> +
>> +#endif
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 1b5a95f..2ec35d7 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -430,16 +430,6 @@ choice
>>         benefit.
>>  endchoice
>>
>> -config CROSS_MEMORY_ATTACH
>> -     bool "Cross Memory Support"
>> -     depends on MMU
>> -     default y
>> -     help
>> -       Enabling this option adds the system calls process_vm_readv and
>> -       process_vm_writev which allow a process with the correct privileges
>> -       to directly read from or write to to another process's address space.
>> -       See the man page for more details.
>> -
>>  #
>>  # UP and nommu archs use km based percpu allocator
>>  #
>> diff --git a/mm/Makefile b/mm/Makefile
>> index b484452..d624084 100644
>> --- a/mm/Makefile
>> +++ b/mm/Makefile
>> @@ -7,10 +7,6 @@ mmu-$(CONFIG_MMU)    := fremap.o highmem.o madvise.o memory.o mincore.o \
>>                          mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
>>                          vmalloc.o pagewalk.o pgtable-generic.o
>>
>> -ifdef CONFIG_CROSS_MEMORY_ATTACH
>> -mmu-$(CONFIG_MMU)    += process_vm_access.o
>> -endif
>> -
>>  obj-y                        := filemap.o mempool.o oom_kill.o fadvise.o \
>>                          maccess.o page_alloc.o page-writeback.o \
>>                          readahead.o swap.o truncate.o vmscan.o shmem.o \
>> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
>> deleted file mode 100644
>> index 8505c92..0000000
>> --- a/mm/process_vm_access.c
>> +++ /dev/null
>> @@ -1,383 +0,0 @@
>> -/*
>> - * linux/mm/process_vm_access.c
>> - *
>> - * Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@xxxxxxxxxxx>, IBM Corp.
>> - *
>> - * This program is free software; you can redistribute it and/or
>> - * modify it under the terms of the GNU General Public License
>> - * as published by the Free Software Foundation; either version
>> - * 2 of the License, or (at your option) any later version.
>> - */
>> -
>> -#include <linux/mm.h>
>> -#include <linux/uio.h>
>> -#include <linux/sched.h>
>> -#include <linux/highmem.h>
>> -#include <linux/ptrace.h>
>> -#include <linux/slab.h>
>> -#include <linux/syscalls.h>
>> -
>> -#ifdef CONFIG_COMPAT
>> -#include <linux/compat.h>
>> -#endif
>> -
>> -/**
>> - * process_vm_rw_pages - read/write pages from task specified
>> - * @pages: array of pointers to pages we want to copy
>> - * @start_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) {
>> -                     if (copy > iov_iter_count(iter))
>> -                             copy = iov_iter_count(iter);
>> -                     copied = iov_iter_copy_from_user(page, iter,
>> -                                     offset, copy);
>> -                     iov_iter_advance(iter, copied);
>> -                     set_page_dirty_lock(page);
>> -             } 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 (PAGE_SIZE * 2)
>> -
>> -/**
>> - * 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 long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
>> -             / sizeof(struct pages *);
>> -
>> -     /* Work out address and page range required */
>> -     if (len == 0)
>> -             return 0;
>> -     nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
>> -
>> -     while (!rc && nr_pages && iov_iter_count(iter)) {
>> -             int pages = min(nr_pages, max_pages_per_loop);
>> -             size_t bytes;
>> -
>> -             /* Get the pages we're interested in */
>> -             down_read(&mm->mmap_sem);
>> -             pages = get_user_pages(task, mm, pa, pages,
>> -                                   vm_write, 0, process_pages, NULL);
>> -             up_read(&mm->mmap_sem);
>> -
>> -             if (pages <= 0)
>> -                     return -EFAULT;
>> -
>> -             bytes = 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 -= pages;
>> -             pa += pages * PAGE_SIZE;
>> -             while (pages)
>> -                     put_page(process_pages[--pages]);
>> -     }
>> -
>> -     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)
>> -                             / 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,
>> -                                           sizeof(struct pages *)*nr_pages),
>> -                                     GFP_KERNEL);
>> -
>> -             if (!process_pages)
>> -                     return -ENOMEM;
>> -     }
>> -
>> -     /* Get process information */
>> -     rcu_read_lock();
>> -     task = find_task_by_vpid(pid);
>> -     if (task)
>> -             get_task_struct(task);
>> -     rcu_read_unlock();
>> -     if (!task) {
>> -             rc = -ESRCH;
>> -             goto free_proc_pages;
>> -     }
>> -
>> -     mm = mm_access(task, PTRACE_MODE_ATTACH);
>> -     if (!mm || IS_ERR(mm)) {
>> -             rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
>> -             /*
>> -              * Explicitly map EACCES to EPERM as EPERM is a more a
>> -              * 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 = iovstack_r;
>> -     struct iov_iter iter;
>> -     ssize_t rc;
>> -
>> -     if (flags != 0)
>> -             return -EINVAL;
>> -
>> -     /* Check iovecs */
>> -     if (vm_write)
>> -             rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
>> -                                        iovstack_l, &iov_l);
>> -     else
>> -             rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
>> -                                        iovstack_l, &iov_l);
>> -     if (rc <= 0)
>> -             goto free_iovecs;
>> -
>> -     iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
>> -
>> -     rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
>> -                                iovstack_r, &iov_r);
>> -     if (rc <= 0)
>> -             goto free_iovecs;
>> -
>> -     rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
>> -
>> -free_iovecs:
>> -     if (iov_r != iovstack_r)
>> -             kfree(iov_r);
>> -     if (iov_l != iovstack_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);
>> -}
>> -
>> -#ifdef CONFIG_COMPAT
>> -
>> -static ssize_t
>> -compat_process_vm_rw(compat_pid_t pid,
>> -                  const struct compat_iovec __user *lvec,
>> -                  unsigned long liovcnt,
>> -                  const struct compat_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 = iovstack_r;
>> -     struct iov_iter iter;
>> -     ssize_t rc = -EFAULT;
>> -
>> -     if (flags != 0)
>> -             return -EINVAL;
>> -
>> -     if (vm_write)
>> -             rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
>> -                                               UIO_FASTIOV, iovstack_l,
>> -                                               &iov_l);
>> -     else
>> -             rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
>> -                                               UIO_FASTIOV, iovstack_l,
>> -                                               &iov_l);
>> -     if (rc <= 0)
>> -             goto free_iovecs;
>> -     iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
>> -     rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
>> -                                       UIO_FASTIOV, iovstack_r,
>> -                                       &iov_r);
>> -     if (rc <= 0)
>> -             goto free_iovecs;
>> -
>> -     rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
>> -
>> -free_iovecs:
>> -     if (iov_r != iovstack_r)
>> -             kfree(iov_r);
>> -     if (iov_l != iovstack_l)
>> -             kfree(iov_l);
>> -     return rc;
>> -}
>> -
>> -COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
>> -                    const struct compat_iovec __user *, lvec,
>> -                    compat_ulong_t, liovcnt,
>> -                    const struct compat_iovec __user *, rvec,
>> -                    compat_ulong_t, riovcnt,
>> -                    compat_ulong_t, flags)
>> -{
>> -     return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
>> -                                 riovcnt, flags, 0);
>> -}
>> -
>> -COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
>> -                    const struct compat_iovec __user *, lvec,
>> -                    compat_ulong_t, liovcnt,
>> -                    const struct compat_iovec __user *, rvec,
>> -                    compat_ulong_t, riovcnt,
>> -                    compat_ulong_t, flags)
>> -{
>> -     return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
>> -                                 riovcnt, flags, 1);
>> -}
>> -
>> -#endif
>>
>> --
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