linux-kernel - Re: [PATCH v3 4/4] tracing/probes: Fix to record 0-length data_loc in fetch_store

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Date:   Tue, 11 Jul 2023 09:05:15 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Dan Carpenter <dan.carpenter@...aro.org>,
        linux-trace-kernel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] tracing/probes: Fix to record 0-length data_loc
 in fetch_store_string*() if fails

On Mon, 10 Jul 2023 18:16:01 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Sat,  8 Jul 2023 11:48:58 +0900
> "Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> 
> > --- a/kernel/trace/trace_probe_kernel.h
> > +++ b/kernel/trace/trace_probe_kernel.h
> > @@ -55,8 +55,7 @@ fetch_store_string_user(unsigned long addr, void *dest, void *base)
> >  	__dest = get_loc_data(dest, base);
> >  
> >  	ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
> > -	if (ret >= 0)
> > -		*(u32 *)dest = make_data_loc(ret, __dest - base);
> > +	*(u32 *)dest = make_data_loc((ret >= 0) ? ret : 0, __dest - base);
> >  
> >  	return ret;
> >  }
> > @@ -87,8 +86,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
> >  	 * probing.
> >  	 */
> >  	ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
> > -	if (ret >= 0)
> > -		*(u32 *)dest = make_data_loc(ret, __dest - base);
> > +	*(u32 *)dest = make_data_loc((ret >= 0) ? ret : 0, __dest - base);
> 
> The above is a complex line, and not something that I think should be cut
> and pasted between two different locations.
> 
> I know you took out the set_data_loc() helper, but really it should have
> stayed, and have used that to update this code in the two places it
> affected, instead of making the changes in those two locations.
> 
> That is, patch 3 could have had kept.
> 
> static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base)
> {
> 	if (ret >= 0)
> 		*(u32 *)dest = make_data_loc(ret, __dest - base);
> }

To avoid confusion, I would like to revert the set_data_loc() at the 3rd patch
and add it again in 4th patch.

> 
> And this patch could have been:
> 
> static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base)
> {
> 	*(u32 *)dest = make_data_loc(ret, __dest - base);
> }

and introduce it. I also want to put the ternary operator into set_data_loc() too
for simplicity.

static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base)
{
	if (ret < 0)
		ret = 0;
	*(u32 *)dest = make_data_loc(ret, __dest - base);
}

Thanks,

> 
> That would keep the complexity down in this changes set.
> 
> -- Steve
> 
> 
> >  
> >  	return ret;
> >  }


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>