Re: [PATCH 1/3] kretprobes: ensure probe location is at function entry

[Masami Hiramatsu <mhiramat@kernel.org>]

On Wed, 15 Feb 2017 23:47:52 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> kretprobes can be registered by specifying an absolute address or by
> specifying offset to a symbol. However, we need to ensure this falls at
> function entry so as to be able to determine the return address.
> 
> Validate the same during kretprobe registration. By default, there
> should not be any offset from a function entry, as determined through a
> kallsyms_lookup(). Introduce arch_function_offset_within_entry() as a
> way for architectures to override this.
> 

Looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks!

> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
> ---
> powerpc64 ABIv2 will need to use the over-ride as we want to use the
> local entry point which will be at an offset of 8 bytes from the
> (global) entry point. I have a patch that I will post separately.
> 
> Thanks,
> Naveen
> 
>  include/linux/kprobes.h |  1 +
>  kernel/kprobes.c        | 13 +++++++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 8f6849084248..0c2489435117 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -266,6 +266,7 @@ extern int arch_init_kprobes(void);
>  extern void show_registers(struct pt_regs *regs);
>  extern void kprobes_inc_nmissed_count(struct kprobe *p);
>  extern bool arch_within_kprobe_blacklist(unsigned long addr);
> +extern bool arch_function_offset_within_entry(unsigned long offset);
>  
>  extern bool within_kprobe_blacklist(unsigned long addr);
>  
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 43460104f119..72ecbf5a6312 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1834,12 +1834,25 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
>  }
>  NOKPROBE_SYMBOL(pre_handler_kretprobe);
>  
> +bool __weak arch_function_offset_within_entry(unsigned long offset)
> +{
> +	return !offset;
> +}
> +
>  int register_kretprobe(struct kretprobe *rp)
>  {
>  	int ret = 0;
>  	struct kretprobe_instance *inst;
>  	int i;
>  	void *addr;
> +	unsigned long offset;
> +
> +	addr = kprobe_addr(&rp->kp);
> +	if (!kallsyms_lookup_size_offset((unsigned long)addr, NULL, &offset))
> +		return -EINVAL;
> +
> +	if (!arch_function_offset_within_entry(offset))
> +		return -EINVAL;
>  
>  	if (kretprobe_blacklist_size) {
>  		addr = kprobe_addr(&rp->kp);
> -- 
> 2.11.0
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>