On Mon, 11 Nov 2002, Post, Mark K wrote: > 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.) > A better source;-)
http://doclib.ucs.indiana.edu/cgi-bin/bookmgr/bookmgr.exe/BOOKS/DZ9AR007/3.3 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: ____ _ _ _ |ACC |F|R|C| |____|_|_|_| 0 4 6 The bit positions in the storage key are allocated as follows: Access-Control Bits (ACC): If a reference is subject to key-controlled protection, the four access-control bits, bits 0-3, are matched with the four-bit access key when information is stored, or when information is fetched from a location that is protected against fetching. 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. Reference Bit (R): The reference bit, bit 5, normally is set to one each time a location in the corresponding storage block is referred to either for storing or for fetching of information. Change Bit (C): The change bit, bit 6, is set to one each time information is stored at a location in the corresponding storage block. Storage keys are not part of addressable storage. The entire storage key is set by SET STORAGE KEY EXTENDED and inspected by INSERT STORAGE KEY EXTENDED. Additionally, the instruction RESET REFERENCE BIT EXTENDED provides a means of inspecting the reference and change bits and of setting the reference bit to zero. Bits 0-4 of the storage key are inspected by the INSERT VIRTUAL STORAGE KEY instruction. The contents of the storage key are unpredictable during and after the execution of the usability test of the TEST BLOCK instruction. > 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? > -- Cheers John. Please, no off-list mail. You will fall foul of my spam treatment. Join the "Linux Support by Small Businesses" list at http://mail.computerdatasafe.com.au/mailman/listinfo/lssb
