On Wed, Aug 3, 2016 at 10:14 AM, Borislav Petkov <[email protected]> wrote: > On Wed, Aug 03, 2016 at 09:42:29AM -0700, Andy Lutomirski wrote: >> I would change "so" and "and" -- the CPU designers could have make >> SYSRET restore RF, but they chose not to. > > I'm assuming the reasoning behind it was that you should be able to > break after SYSRET but then again, the kernel could've been left in > control of that bit and set it or clear it however it likes before > SYSRETing. > > Oh well.
AFAICT the AMD people didn't think of any use cases involving doing anything interesting between SYSCALL and SYSRET. Witness the sysret_ss_attrs goof, for example: apparently SYSCALL; context switch; IRET; interrupt; context switch; SYSRET didn't occur to AMD as a valid use case. --Andy
