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question to STL

Created by: nhtuvay at: 8/26/2013 3:25 PM (11 Replies)

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8/26/2013 3:25 PM	Rate (0)
nhtuvay Posts: 4 Rating: (0)	Hi Everybody, Related to this subject, I want to learn something about STL; I am new about PLCs and got training from SITRAIN, for the starting levels (Hardware and software). Now I am studying STL. Last week, my company updated all the software with STL and the person who updated, has quited the job. Although he was a good guy, we are uncertain about the code. The only thing that I want to learn;-While a remote possibility- is it possible to write a code in STL; like "after this date, delete all data and/or software". In other words, is it possible to write a worm like code with STL?
nhtuvay Posts: 4 Rating: (0)	Last edited by: Blue Moderator at: 26.08.2013 16:11 new subject after splitting from /tf/WW/de/Posts/87766#top
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8/27/2013 8:29 AM	Rate (0)
Marcjan Diamond Member Joined: 4/22/2010 Last visit: 3/31/2025 Posts: 5697 Rating: (716)	Hello, Not exactly a worm or something, but it is possible to write code that will clear DB's or even put the PLC in stop at some time. That kind of sabotage can be done in any program language. STL is not some scary secret language in wich you can hide such code and no one will know. If you know ho to look you will find such program verry quickly, unles the blocks are protected. Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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8/27/2013 8:41 AM	Rate (0)
nhtuvay Posts: 4 Rating: (0)	Thank you Marcjan, Now I have a better understanding with the help of your explanation. So; as I understood, a simple sabotage "code" could be inserted into the DB's; or somewhere else. At the moment I do not have satisfactory knowledge in STL; but I thought it could be impossible to write a self-destructing code. So, I was wrong. Now, I think, I have to check all the DB's to detect a "suspicious" code block... By the way, I am studying STL form the book "Automating with STEP7 in STL and SCL" - Hans Berger. As an expert; could you please advice me another source(s) ? Thanks & Regards
nhtuvay Posts: 4 Rating: (0)
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8/27/2013 8:56 AM	Rate (0)
playerslight Posts: 1064 Rating: (72)	another place to lok is under simatic documentation there you should fine working with statement list .this si a default install with your step 7 software and using the search function here there is a lot of manuals and helpful information available if you come across cos ethat you ar enot sure post it and someone will explain it to you
playerslight Posts: 1064 Rating: (72)	Last edited by: playerslight at: 8/27/2013 8:57 AM
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8/27/2013 9:35 AM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 12/29/2025 Posts: 5149 Rating: (772)	nhtuvay <snip> So; as I understood, a simple sabotage "code" could be inserted into the DB's; or somewhere else. <snip> Now, I think, I have to check all the DB's to detect a "suspicious" code block... <snip> No. Any code can only be placed in OB's, FB's or FC's. DB's hold only data which can't be executed (program memory and data memory in S7 are separated). BTW, themost nasty thing which comes to my mind in case of S7 software is to use an indirect addressing based on some pointer stored in the memory. And then deleting thispointer during runtime.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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8/27/2013 12:16 PM	Rate (0)
nhtuvay Posts: 4 Rating: (0)	jacek d No. Any code can only be placed in OB's, FB's or FC's. DB's hold only data which can't be executed (program memory and data memory in S7 are separated). BTW, themost nasty thing which comes to my mind in case of S7 software is to use an indirect addressing based on some pointer stored in the memory. And then deleting thispointer during runtime. Thank you jacek d. Your information is helpful but I am a little bit confused; <snip> BTW, the most nasty thing which comes to my mind in case of S7 software is to use an indirect addressing based on some pointer stored in the memory. And then deleting this pointer during runtime. <snip> So, is it possible to find this kind of code; to where should I look?
nhtuvay Posts: 4 Rating: (0)
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8/28/2013 10:21 AM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 12/29/2025 Posts: 5149 Rating: (772)	nhtuvay So, is it possible to find this kind of code; to where should I look? Yes of course. Look in the code for something similar to [AR1,p#x.y] or [AR2,p#x.y] where x,y are numbers.
	Last edited by: jacek d at: 8/28/2013 11:03 AM Wrong placement of BBcode tags. Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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8/28/2013 10:55 AM	Rate (0)
Ste39 Posts: 4620 Rating: (710)	Hi nhtuvay, You may also see some SFC, such as SFC 46 STOP, or SFC 51 RDSYSST going to read the serial number of the MMC and then do something else, it's just a thought.
Ste39 Posts: 4620 Rating: (710)
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8/28/2013 1:44 PM	Rate (0)
Rick D Posts: 43 Rating: (0)	Hi Everyone, In reply to the previous comment, does it mean that having SFC 46 STOP, or SFC 51 in the code is abnormal. Can someone explain the function of SFC 51 in brief.
Rick D Posts: 43 Rating: (0)
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8/28/2013 2:23 PM	Rate (1)
Ste39 Posts: 4620 Rating: (710)	Hi no it is not abnormal, if you want then you can use, such as for SFC 46 STOP, if you want to send to stop the CPU from an HMI instead of PG or for some reason. For SFC 51 look here: sample program for SFC 51 - Siemens Industry Online ... or go to 13-3:Reference Manual for S7-300/400 System and Standard ... - Siemens
Ste39 Posts: 4620 Rating: (710)	Last edited by: Ste39 at: 8/28/2013 2:39 PM Last edited by: Ste39 at: 8/28/2013 2:25 PM
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This contribution was helpful to 1 thankful Users Rick D

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