"Other operating systems" and "stealing" a bit

Posted Feb 23, 2022 19:31 UTC (Wed) by jthill (subscriber, #56558)
In reply to: "Other operating systems" and "stealing" a bit by epa
Parent article: Shadow stacks for user space

It took me a bit too.

That part of the discussion is about hardware support for shadow stacks. The hardware PTEs have so-far-unused bits, left uninterpreted and unchecked so they're available to operating systems. Linux doesn't use all of those bits, but other operating systems do. So the hardware engineers implementing hardware-shadow-stack support were loath to claw back a PTE bit because it'd break those other operating systems.

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"Other operating systems" and "stealing" a bit

Posted Feb 23, 2022 19:59 UTC (Wed) by zdzichu (subscriber, #17118) [Link] (1 responses)

It is interesting that HW guys choose the solution which required modification in Linux. The "other system" (could we guess it was MS Windows?) used all bits, so instead telling "change your ways and do as Linux do", they told Linux "you have to change". Isn't that unfair?

"Other operating systems" and "stealing" a bit

Posted Feb 23, 2022 20:16 UTC (Wed) by corbet (editor, #1) [Link]

All operating systems will need changes to make use of this feature; it doesn't seem all that terrible if asking this particular change from Linux turned out to be the path of least resistance. Especially since Intel is actually doing the work to effect that change.