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    Subject[PATCH v5 05/23] fork: Provide a function for copying init_mm
    Date
    Provide a function for copying init_mm. This function will be later used
    for setting a temporary mm.

    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
    Tested-by: Masami Hiramatsu <mhiramat@kernel.org>
    Signed-off-by: Nadav Amit <namit@vmware.com>
    Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
    ---
    include/linux/sched/task.h | 1 +
    kernel/fork.c | 24 ++++++++++++++++++------
    2 files changed, 19 insertions(+), 6 deletions(-)

    diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
    index 2e97a2227045..f1227f2c38a4 100644
    --- a/include/linux/sched/task.h
    +++ b/include/linux/sched/task.h
    @@ -76,6 +76,7 @@ extern void exit_itimers(struct signal_struct *);
    extern long _do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *, unsigned long);
    extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
    struct task_struct *fork_idle(int);
    +struct mm_struct *copy_init_mm(void);
    extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
    extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);

    diff --git a/kernel/fork.c b/kernel/fork.c
    index 9dcd18aa210b..099cca8f701c 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -1298,13 +1298,20 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
    complete_vfork_done(tsk);
    }

    -/*
    - * Allocate a new mm structure and copy contents from the
    - * mm structure of the passed in task structure.
    +/**
    + * dup_mm() - duplicates an existing mm structure
    + * @tsk: the task_struct with which the new mm will be associated.
    + * @oldmm: the mm to duplicate.
    + *
    + * Allocates a new mm structure and duplicates the provided @oldmm structure
    + * content into it.
    + *
    + * Return: the duplicated mm or NULL on failure.
    */
    -static struct mm_struct *dup_mm(struct task_struct *tsk)
    +static struct mm_struct *dup_mm(struct task_struct *tsk,
    + struct mm_struct *oldmm)
    {
    - struct mm_struct *mm, *oldmm = current->mm;
    + struct mm_struct *mm;
    int err;

    mm = allocate_mm();
    @@ -1371,7 +1378,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
    }

    retval = -ENOMEM;
    - mm = dup_mm(tsk);
    + mm = dup_mm(tsk, current->mm);
    if (!mm)
    goto fail_nomem;

    @@ -2186,6 +2193,11 @@ struct task_struct *fork_idle(int cpu)
    return task;
    }

    +struct mm_struct *copy_init_mm(void)
    +{
    + return dup_mm(NULL, &init_mm);
    +}
    +
    /*
    * Ok, this is the main fork-routine.
    *
    --
    2.17.1
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