linux-kernel - Re: [PATCH] tracing: Verify event formats that have "%*p.."

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Message-ID: <d9707265-d6bd-40df-8e7f-4213851ea33f@oracle.com>
Date: Thu, 27 Mar 2025 14:00:44 -0700
From: Libo Chen <libo.chen@...cle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: Verify event formats that have "%*p.."



On 3/27/25 11:38, Steven Rostedt wrote:
> On Thu, 27 Mar 2025 11:32:23 -0700
> Libo Chen <libo.chen@...cle.com> wrote:
> 
>> On 3/27/25 08:49, Steven Rostedt wrote:
>>> From: Steven Rostedt <rostedt@...dmis.org>
>>>
>>> The trace event verifier checks the formats of trace events to make sure
>>> that they do not point at memory that is not in the trace event itself or
>>> in data that will never be freed. If an event references data that was
>>> allocated when the event triggered and that same data is freed before the
>>> event is read, then the kernel can crash by reading freed memory.
>>>
>>> The verifier runs at boot up (or module load) and scans the print formats
>>> of the events and checks their arguments to make sure that dereferenced
>>> pointers are safe. If the format uses "%*p.." the verifier will ignore it,
>>> and that could be dangerous. Cover this case as well.
>>>
>>> Also add to the sample code a use case of "%*pbl".
>>>
>>> Link: https://urldefense.com/v3/__https://lore.kernel.org/all/bcba4d76-2c3f-4d11-baf0-02905db953dd@oracle.com/__;!!ACWV5N9M2RV99hQ!LTIVO1_O9wY2hBAnpNF5zcB1EFlC77zOnu4oVcM4DoD77p5ZO_m1LFZdPVJPj4spzye4JntXHOqOVxirPQ$ 
>>>   
>> Thanks Steve, a minor style issue below, otherwise LGTM. I have tested it, it works. 
>>
>> Reviewed-by: Libo Chen <libo.chen@...cle.com>
>> Tested-by: Libo Chen <libo.chen@...cle.com>
> 
> Thanks for testing.
> 
>>>  /*
>>>   * Notice here the use of some helper functions. This includes:
>>> @@ -370,7 +371,10 @@ TRACE_EVENT(foo_bar,
>>>  
>>>  		  __get_str(str), __get_str(lstr),
>>>  		  __get_bitmask(cpus), __get_cpumask(cpum),
>>> -		  __get_str(vstr))
>>> +		  __get_str(vstr),
>>> +	         __get_dynamic_array_len(cpus),
>>> +	         __get_dynamic_array_len(cpus),
>>> +	         __get_dynamic_array(cpus))  
>>
>> __get_dynamic_array_len() calls don't seem to be aligned with the ones above
>>
> 
> Ah yeah. I'll update. Note, this isn't going to go into the kernel until at
> least 6.16.
> 

Okay thanks for the note. I will stick to %lx for now and change it to %*pbl
once this gets in.

Libo 

> -- Steve