On 22/03/2023 2:22 am, Li, Xin3 wrote: >> If there is no other concrete reason other than overflowing for assigning NMI and >> #DB with a stack level > 0, #VE should also be assigned with a stack level > 0, and >> #BP too. #VE can happen anytime and anywhere, so it is subject to overflowing too. > With IDT, both #VE and #BP do not use IST, but NMI, #DB, #MC and #DF do. > > Let's keep this "secret" logic for now, i.e., not change the stack levels > for #VE and #BP at this point. We can do "optimization", i.e., change them > later :). Fun fact. #BP used to be IST, and used to share the same IST as #DF. This was spoiled by CVE-2018-8897 and a MovSS-delayed breakpoint over INT3, at which point hardware queued both a #BP and #DB on the same IST stack and lost program state. There's no need specific need for #BP to be IST to begin with, hence why making it not-IST was the security fix. ~Andrew
