[CRIU] [PATCH] ptrace: flush breakpoints

[Pavel Emelyanov]

On 09/19/2014 11:48 PM, Andrey Vagin wrote:
> Unfortunately the kernel doesn't flush hw breakpoints on
> detaching ptrace. If a breakpoint is triggered without ptrace, it
> will be killed by SIGTRAP.
> 
> Reported-by: Mr Jenkins
> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>  arch/aarch64/include/asm/restorer.h |  5 +++++
>  arch/arm/include/asm/restorer.h     |  5 +++++
>  arch/x86/crtools.c                  | 13 +++++++++++++
>  arch/x86/include/asm/restorer.h     |  1 +
>  cr-restore.c                        | 15 +++++++++++++++
>  parasite-syscall.c                  |  3 +++
>  6 files changed, 42 insertions(+)
> 
> diff --git a/arch/aarch64/include/asm/restorer.h b/arch/aarch64/include/asm/restorer.h
> index 53c3847..61e8576 100644
> --- a/arch/aarch64/include/asm/restorer.h
> +++ b/arch/aarch64/include/asm/restorer.h
> @@ -113,4 +113,9 @@ static inline int ptrace_set_breakpoint(pid_t pid, void *addr)
>  	return 0;
>  }
>  
> +static inline int ptrace_flush_breakpoints(pid_t pid)
> +{
> +	return 0;
> +}
> +
>  #endif
> diff --git a/arch/arm/include/asm/restorer.h b/arch/arm/include/asm/restorer.h
> index 36ce4e9..8acb2d3 100644
> --- a/arch/arm/include/asm/restorer.h
> +++ b/arch/arm/include/asm/restorer.h
> @@ -155,4 +155,9 @@ static inline int ptrace_set_breakpoint(pid_t pid, void *addr)
>  	return 0;
>  }
>  
> +static inline int ptrace_flush_breakpoints(pid_t pid)
> +{
> +	return 0;
> +}
> +
>  #endif
> diff --git a/arch/x86/crtools.c b/arch/x86/crtools.c
> index 1248975..cbbcb9d 100644
> --- a/arch/x86/crtools.c
> +++ b/arch/x86/crtools.c
> @@ -540,3 +540,16 @@ int ptrace_set_breakpoint(pid_t pid, void *addr)
>  	return 1;
>  }
>  
> +int ptrace_flush_breakpoints(pid_t pid)
> +{
> +	/* Disable the breakpoint */
> +	if (ptrace(PTRACE_POKEUSER, pid,
> +			offsetof(struct user, u_debugreg[DR_CONTROL]),
> +			0)) {
> +		pr_err("Unable to disable the breakpoint\n");
> +		return -1;
> +	}
> +
> +	return 0;
> +}
> +
> diff --git a/arch/x86/include/asm/restorer.h b/arch/x86/include/asm/restorer.h
> index 00d4977..70199fb 100644
> --- a/arch/x86/include/asm/restorer.h
> +++ b/arch/x86/include/asm/restorer.h
> @@ -146,6 +146,7 @@ int sigreturn_prep_fpu_frame(struct rt_sigframe *sigframe, fpu_state_t *fpu_stat
>  static inline void restore_tls(tls_t *ptls) { (void)ptls; }
>  
>  int ptrace_set_breakpoint(pid_t pid, void *addr);
> +int ptrace_flush_breakpoints(pid_t pid);
>  
>  
>  #endif
> diff --git a/cr-restore.c b/cr-restore.c
> index 809564b..7141c6c 100644
> --- a/cr-restore.c
> +++ b/cr-restore.c
> @@ -1599,6 +1599,18 @@ static int attach_to_tasks(bool root_seized, enum trace_flags *flag)
>  	return 0;
>  }
>  
> +static int clear_breakpoints()
> +{
> +	struct pstree_item *item;
> +	int ret = 0, i;
> +
> +	for_each_pstree_item(item)
> +		for (i = 0; i < item->nr_threads; i++)
> +			ret |= ptrace_flush_breakpoints(item->threads[i].real);

Can we optimize this loop out on arches that don't support
breakpoints?

> +
> +	return ret;
> +}
> +
>  static void finalize_restore(int status)
>  {
>  	struct pstree_item *item;
> @@ -1775,6 +1787,9 @@ static int restore_root_task(struct pstree_item *init)
>  		ret = parasite_stop_on_syscall(task_entries->nr_threads,
>  						__NR_rt_sigreturn, flag);
>  
> +	if (clear_breakpoints())
> +		pr_err("Unable to flush breakpoints\n");
> +
>  	/*
>  	 * finalize_restore() always detaches from processes and
>  	 * they continue run through sigreturn.
> diff --git a/parasite-syscall.c b/parasite-syscall.c
> index 37e9db0..9102b23 100644
> --- a/parasite-syscall.c
> +++ b/parasite-syscall.c
> @@ -890,6 +890,9 @@ static int parasite_fini_seized(struct parasite_ctl *ctl)
>  	if (parasite_stop_on_syscall(1, __NR_rt_sigreturn, flag))
>  		return -1;
>  
> +	if (ptrace_flush_breakpoints(pid))
> +		return -1;
> +
>  	/*
>  	 * All signals are unblocked now. The kernel notifies about leaving
>  	 * syscall before starting to deliver signals. All parasite code are
>