Re: [PATCH v2 07/11] uprobes/x86: Reimplement arch_uretprobe_is_alive()

[Anton Arapov <arapov@gmail.com>]

On Tue, Jul 07, 2015 at 03:22:58AM +0200, Oleg Nesterov wrote:
> Add the x86-specific version of arch_uretprobe_is_alive() helper.
> It returns true if the stack frame mangled by prepare_uretprobe()
> is still on stack. So if it returns false, we know that the probed
> function has already returned.
> 
> We add the new return_instance->stack member and change the generic
> code to initialize it in prepare_uretprobe, but it should be equally
> useful for other architectures.
> 
> TODO: this assumes that the probed application can't use multiple
> stacks (say sigaltstack). We will try to improve this logic later.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Anton Arapov <arapov@gmail.com>

> ---
>  arch/x86/kernel/uprobes.c |    5 +++++
>  include/linux/uprobes.h   |    1 +
>  kernel/events/uprobes.c   |    1 +
>  3 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 0b81ad6..9d5f570 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -993,3 +993,8 @@ arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs
>  
>  	return -1;
>  }
> +
> +bool arch_uretprobe_is_alive(struct return_instance *ret, struct pt_regs *regs)
> +{
> +	return regs->sp <= ret->stack;
> +}
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 50d2764..7ab6d2c 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -95,6 +95,7 @@ struct uprobe_task {
>  struct return_instance {
>  	struct uprobe		*uprobe;
>  	unsigned long		func;
> +	unsigned long		stack;		/* stack pointer */
>  	unsigned long		orig_ret_vaddr; /* original return address */
>  	bool			chained;	/* true, if instance is nested */
>  
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 1c71b62..c5f316e 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1562,6 +1562,7 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
>  
>  	ri->uprobe = get_uprobe(uprobe);
>  	ri->func = instruction_pointer(regs);
> +	ri->stack = user_stack_pointer(regs);
>  	ri->orig_ret_vaddr = orig_ret_vaddr;
>  	ri->chained = chained;
>  
> -- 
> 1.5.5.1
>