> -----Original Message----- > From: Post, Mark K [mailto:mark.post@;eds.com] > Sent: Monday, November 11, 2002 1:28 PM > To: [EMAIL PROTECTED] > Subject: Re: CPU Arch Security [was: Re: Probably the first > published shel l code] > > > 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 >
Not entirely true, but it can be a bit complicated. If the PSW key is zero, then it can fetch from any page and store into any page except: addresses 0-511 if "low address protection" is turned on. (and bytes 4096-4607 in zArchitecture mode as well) The page table entry for the address is marked as "read only". If the PSW key is not zero and matches the key of the piece of storage, it can store into the page unless the page table entry is marked as "read only". It can always fetch the contents of the page. If the PSW key is not zero and does not match the key in storage, it cannot store into the page under any conditions. (Well, this is a lie, but even more complicated due to "subspace groups" which are not used in Linux/390). It can fetch from the page if the "fetch protect" bit is *not* on. If the "fetch protect" bit is on, then it will get an interrupt code 4. -- John McKown Senior Technical Specialist UICI Insurance Center Applications & Solutions Team +1.817.255.3225
