Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH] sched/scs: Reset the shadow stack when idle_task_exit | Date | Tue, 12 Oct 2021 10:59:54 +0100 |
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On 12/10/21 16:35, Woody Lin wrote: > There was a 'init_idle' that resets scs sp to base, but is removed by > f1a0a376ca0c. Without the resetting, the hot-plugging implemented by > cpu_psci_cpu_boot will use the previous scs sp as new base when starting > up a CPU core, so the usage on scs page is being stacked up until > overflow. > > This only happens on idle task since __cpu_up is using idle task as the > main thread to start up a CPU core, so the overflow can be fixed by > resetting scs sp to base in 'idle_task_exit'. >
Looking at init_idle() for similar issues, it looks like we might also want to re-issue kasan_unpoison_task_stack() on the idle task upon hotplug.
> Fixes: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled") > Signed-off-by: Woody Lin <woodylin@google.com> > --- > kernel/sched/core.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 1bba4128a3e6..f21714ea3db8 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -8795,6 +8795,7 @@ void idle_task_exit(void) > finish_arch_post_lock_switch(); > } > > + scs_task_reset(current); > /* finish_cpu(), as ran on the BP, will clean up the active_mm state */
So AIUI for SCS that works just fine - one thing I'm unclear on is how the following pops are going to work given the SP reset happens in the middle of a call stack, but AFAICT that was already the case before I messed about with init_idle(), so that must already be handled.
I'm not familiar enough with KASAN to say whether that kasan_unpoison_task_stack() should rather happen upon hotplugging the CPU back (rather than on hot-unplug). If that is the case, then maybe somewhere around cpu_startup_entry() might work (and then you could bunch these two "needs to be re-run at init for the idle task" functions into a common helper).
> } > > -- > 2.33.0.882.g93a45727a2-goog
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