linux-kernel - Re: [RFC PATCH 3/6] fork: provide a function for copying init

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Message-Id: <20180829185428.e59fe325efcd4eb675e3eee3@kernel.org>
Date:   Wed, 29 Aug 2018 18:54:28 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
        <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        <linux-arch@...r.kernel.org>, Andy Lutomirski <luto@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 3/6] fork: provide a function for copying init_mm

On Wed, 29 Aug 2018 01:11:44 -0700
Nadav Amit <namit@...are.com> wrote:

> Provide a function for copying init_mm. This function will be later used
> for setting a temporary mm.

This looks good to me :)

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks!

> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Nadav Amit <namit@...are.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 108ede99e533..ac0a675678f5 100644
> --- a/include/linux/sched/task.h
> +++ b/include/linux/sched/task.h
> @@ -74,6 +74,7 @@ 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 d896e9ca38b0..a1c637b903c1 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1254,13 +1254,20 @@ 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 copy contents from the provided
> + * @oldmm structure.
> + *
> + * 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();
> @@ -1327,7 +1334,7 @@ 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;
>  
> @@ -2127,6 +2134,11 @@ 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
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>