Re: CPU Arch Security [was: Re: Probably the first published shel l code]

[Michael Short]

The keys don't have to match if the fetch pretection bit is 0. See from
z/900 PofO:

3.3 Storage Key
A  storage  key  is  associated with each 4K-byte block of storage that is
available in the configuration.  The storage key has the following format:

‚€€€€ˆ€ˆ€ˆ€ƒ
�ACC �F�R�C�
„€€€€‰€‰€‰€…
0          4    6

Fetch-Protection  Bit  (F):   If  a reference is subject to key-controlled
protection,  the   fetch-protection   bit,   bit   4,   controls   whether
key-controlled  protection  applies  to  fetch-type  references:    a zero
indicates that only store-type references are monitored and that  fetching
with  any  access  key  is  permitted; a one indicates that key-controlled
protection applies to both fetching and storing.  No distinction  is  made
between the fetching of instructions and of operands.




                                                                                       
                                                
                                                                                       
                                                
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                      "Post, Mark K"           cc:       (bcc: Michael Short/Towers 
Perrin)                                            
                      <[EMAIL PROTECTED]        Subject:  Re: CPU Arch Security [was: 
Re: Probably the first published shel l           
                      m>                        code]                                  
                                                
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                      11/11/2002 02:27                                                 
                                                
                      PM                                                               
                                                
                      Please respond to                                                
                                                
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Linas,

No.  Either your storage key matches, or it doesn't.  If it matches, you
get
read and write access, if it doesn't match, you get neither.  (You _do_ get
a S0C4 abend.)

Mark Post

-----Original Message-----
From: Linas Vepstas [mailto:linas@;linas.org]
Sent: Monday, November 11, 2002 12:57 PM
To: [EMAIL PROTECTED]
Subject: Re: CPU Arch Security [was: Re: Probably the first published
shell code]


-snip-
It has been years since I last looked at the 390 instruction set.  Can't
one
set a read-only mode for selected PSW keys?