On Fri, Oct 18, 2019 at 10:35:49AM -0700, Sami Tolvanen wrote: > On Fri, Oct 18, 2019 at 10:23 AM Mark Rutland <mark.rutland@xxxxxxx> wrote: > > I think scs_save() would better live in assembly in cpu_switch_to(), > > where we switch the stack and current. It shouldn't matter whether > > scs_load() is inlined or not, since the x18 value _should_ be invariant > > from the PoV of the task. > > Note that there's also a call to scs_save in cpu_die, because the > current task's shadow stack pointer is only stored in x18 and we don't > want to lose it. > > > We just need to add a TSK_TI_SCS to asm-offsets.c, and then insert a > > single LDR at the end: > > > > mov sp, x9 > > msr sp_el0, x1 > > #ifdef CONFIG_SHADOW_CALL_STACK > > ldr x18, [x1, TSK_TI_SCS] > > #endif > > ret > > TSK_TI_SCS is already defined, so yes, we could move this to > cpu_switch_to. I would still prefer to have the overflow check that's > in scs_thread_switch though. The only bit that I think needs to be in cpu_switch_to() is the install of the next task's shadow addr into x18. Having a separate scs_check_overflow() sounds fine to me, as that only has to read from the shadow stack. IIUC that's also for the prev task, not next, in the current patches. Thanks, Mark.
