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Re: Avoiding memory access vulnerabilities

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Am Sat, 27 Feb 2016 15:31:05 +0000 schrieb Anton Ertl:

> Bernd Paysan <bernd.paysan@gmx.de> writes:
>>Am Sat, 27 Feb 2016 07:15:05 +0000 schrieb Anton Ertl:
>>Having a dictionary layout similar to a Flash system (write-once code in
>>one segment, write-many buffers and variables in another segment) could
>>prevent accidential overwriting of code.
> 
> I am not sure that accidental overwriting of data is better (even if it
> is not code addresses).

Depends on the data.  You want to overwrite deferred words or similar to 
get remote execution.  The usual layout of a flash-based Forth has only 
the buffer or the variable space in read-write RAM, and all the rest 
(including headers and code fields) is in flash.

This is "good enough" even for native code Forths, as on current 
processors, data can be in the data and the code cache as long as it is 
accessed read-only, which the headers are.

Things an attacker want to overwrite:

* code
* pointers to code
* vtable pointers (pointers to pointers to code)
* data that is evaluated by jump tables (index to pointers to code)

The more direct the control, the better.

For buffer writes, we usually have words that take addr len instead of 
just addr as in libc (with a bunch of recent replacement words which do 
take a length).  The problem is that the buffers itself don't keep the 
length, especially with BUFFER: we screwed up: It should really return an 
addr len pair, so that e.g.

256 buffer: line

...
line fd read-line throw

would be straight-forward.  Instead, you have to write

line 256 fd read-line throw

and then maybe you run into RAM pressure, decide that 128 bytes is enough 
for a line, but forget to adjust the code that uses read-line.

-- 
Bernd Paysan
"If you want it done right, you have to do it yourself"
net2o ID: kQusJzA;7*?t=uy@X}1GWr!+0qqp_Cn176t4(dQ*
http://bernd-paysan.de/

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Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-26 13:38 +0000
  Re: Avoiding memory access vulnerabilities Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-02-26 16:05 +0000
  Re: Avoiding memory access vulnerabilities Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-02-26 17:18 -0500
    Re: Avoiding memory access vulnerabilities Raimond Dragomir <raimond.dragomir@gmail.com> - 2016-02-26 22:53 -0800
    Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-27 07:15 +0000
      Re: Avoiding memory access vulnerabilities Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-02-27 04:54 -0600
      Re: Avoiding memory access vulnerabilities Bernd Paysan <bernd.paysan@gmx.de> - 2016-02-27 14:27 +0000
        Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-27 15:31 +0000
          Re: Avoiding memory access vulnerabilities Bernd Paysan <bernd.paysan@gmx.de> - 2016-03-01 16:30 +0000
            Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-02 10:04 +0000
              Re: Avoiding memory access vulnerabilities Doug Hoffman <glidedog@gmail.com> - 2016-03-02 08:41 -0500
              Re: Avoiding memory access vulnerabilities Bernd Paysan <bernd.paysan@gmx.de> - 2016-03-02 23:22 +0000
                Re: Avoiding memory access vulnerabilities humptydumpty <ouatubi@gmail.com> - 2016-03-02 22:57 -0800
                Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-03 13:50 +0000
                Re: Avoiding memory access vulnerabilities Bernd Paysan <bernd.paysan@gmx.de> - 2016-03-04 21:01 +0000
                Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-06 10:55 +0000
      Re: Avoiding memory access vulnerabilities Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-02-27 11:31 -0500
        Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-27 17:14 +0000
  Re: Avoiding memory access vulnerabilities Ron Aaron <rambamist@gmail.com> - 2016-02-27 18:59 +0200
    Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-27 17:04 +0000
      Re: Avoiding memory access vulnerabilities Ron Aaron <rambamist@gmail.com> - 2016-02-27 19:18 +0200
        Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-02-28 14:21 +0000
  Re: Avoiding memory access vulnerabilities "Elizabeth D. Rather" <erather@forth.com> - 2016-03-02 21:18 -1000
    Re: Avoiding memory access vulnerabilities Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-03-03 10:23 +0000
      Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-03 14:22 +0000
    Re: Avoiding memory access vulnerabilities Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-03-03 04:53 -0600
      Re: Avoiding memory access vulnerabilities Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-03-03 13:15 +0000
        Re: Avoiding memory access vulnerabilities Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-03-04 04:34 -0600
          Re: Avoiding memory access vulnerabilities Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-03-04 04:56 -0600
            Re: Avoiding memory access vulnerabilities Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-03-04 12:07 +0000
              Re: Avoiding memory access vulnerabilities Andrew Haley <andrew29@littlepinkcloud.invalid> - 2016-03-04 09:48 -0600
              Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-04 17:11 +0000
          Re: Avoiding memory access vulnerabilities Albert van der Horst <albert@spenarnc.xs4all.nl> - 2016-03-04 11:55 +0000
    Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-03 11:33 +0000
      Re: Avoiding memory access vulnerabilities Rod Pemberton <NoHaveNotOne@bcczxcfre.cmm> - 2016-03-04 20:55 -0500
    Re: Avoiding memory access vulnerabilities Mark Wills <markwills1970@gmail.com> - 2016-03-05 02:55 -0800
      Re: Avoiding memory access vulnerabilities "Elizabeth D. Rather" <erather@forth.com> - 2016-03-10 22:39 -0800
        Re: Avoiding memory access vulnerabilities anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2016-03-12 12:44 +0000

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