[CRIU] [PATCH] restore: Don't unmap vdso proxy on final cleanup

[Andrew Vagin]

On Wed, Oct 30, 2013 at 12:54:11AM +0400, Cyrill Gorcunov wrote:
> In case if we need to use vdso proxy the memory area
> which holds restorer also has a place for vdso proxy
> code itself, so on final pass we should not unmap it,
> otherwise any call to vdso function will cause sigsegv.
> 
> IOW, the memory before final "cleanup" pass of restorer
> might look as
> 
>     +-----------+---------+     +-------------+------+
>     | bootstrap | rt-vdso | ... | application | vdso |
>     +-----------+---------+     +-------------+------+
>                        ^                         |
>                        `-------------------------+
> 
> and we have redirected "vdso" code to jump to "rt-vdso".
> After final pass the memory must look as
> 
>                 +---------+     +-------------+------+
>                 | rt-vdso | ... | application | vdso |
>                 +---------+     +-------------+------+
>                        ^                         |
>                        `-------------------------+
> 
> I noticed this problem during container migration
> testing, the container itself was suspended on 2.6.32
> OpenVZ kernel with apache running inside, and any attempt
> to connect to apache caused apache to crash.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  cr-restore.c       | 1 +
>  include/restorer.h | 1 +
>  pie/restorer.c     | 4 +++-
>  3 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/cr-restore.c b/cr-restore.c
> index e219bca..eca540a 100644
> --- a/cr-restore.c
> +++ b/cr-restore.c
> @@ -2395,6 +2395,7 @@ static int sigreturn_restore(pid_t pid, CoreEntry *core)
>  
>  	task_args->bootstrap_start = bootstrap_start;
-  	task_args->bootstrap_len = restore_bootstrap_len;
+	task_args->bootstrap_len = restore_bootstrap_len - vdso_rt_size;

one line fix;)

> +	task_args->vdso_rt_size = vdso_rt_size;
>  
>  	/*
>  	 * Get a reference to shared memory area which is
> diff --git a/include/restorer.h b/include/restorer.h
> index 18a82d8..1ee1539 100644
> --- a/include/restorer.h
> +++ b/include/restorer.h
> @@ -127,6 +127,7 @@ struct task_restore_core_args {
>  
>  	void				*bootstrap_start;
>  	unsigned long			bootstrap_len;
> +	unsigned long			vdso_rt_size;
>  
>  	struct itimerval		itimers[3];
>  
> diff --git a/pie/restorer.c b/pie/restorer.c
> index a8706d9..43cb8f1 100644
> --- a/pie/restorer.c
> +++ b/pie/restorer.c
> @@ -513,10 +513,11 @@ static void restore_posix_timers(struct task_restore_core_args *args)
>  }
>  static void *bootstrap_start;
>  static unsigned int bootstrap_len;
> +static unsigned long vdso_rt_size;
>  
>  void __export_unmap(void)
>  {
> -	sys_munmap(bootstrap_start, bootstrap_len);
> +	sys_munmap(bootstrap_start, bootstrap_len - vdso_rt_size);
>  	/*
>  	 * sys_munmap must not return here. The controll process must
>  	 * trap us on the exit from sys_munmap.
> @@ -589,6 +590,7 @@ long __export_restore_task(struct task_restore_core_args *args)
>  
>  	bootstrap_start = args->bootstrap_start;
>  	bootstrap_len	= args->bootstrap_len;
> +	vdso_rt_size	= args->vdso_rt_size;
>  
>  	task_entries = args->task_entries;
>  
> -- 
> 1.8.3.1
> 
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