On Tue, Aug 06, 2019 at 07:08:51AM +0200, Borislav Petkov wrote: > On Mon, Aug 05, 2019 at 10:50:30AM -0700, Thomas Garnier wrote: > > I saw that %rdx was used for temporary usage and restored before the > > end so I assumed that it was not an option. > > PUSH_AND_CLEAR_REGS saves all regs earlier so I think you should be > able to use others. Like SAVE_AND_SWITCH_TO_KERNEL_CR3/RESTORE_CR3, for > example, uses %r15 and %r14. AFAICT the CONFIG_DEBUG_ENTRY thing he's changing is before we setup pt_regs. Also consider the UNWIND hint that's in there, it states we only have the IRET frame on stack, not a full regs set.
