Commit a52bcdb8 authored Sep 09, 2020 by Haitao Shan

ANDROID: Setting up GS before calling __restore_processor_state.



Android Common Kernel compiled by clang with Shadow Call Stack will
use GS segment. However, __restore_processor_state is called when
system wakes up from S3 and at the moment GS is not restored yet.

This is a hack by copying a small code snippet(setting gs base) from
__restore_processor_state to restore_processor_state. It prepares GS
before __restore_processor_state is called. At the same time,
restore_processor_state is still small enough so that SCS is not on,
as SCS seems to be on only for large functions.

Bug: 166163480
Change-Id: I3bfe4ac61dee876da57de6578c9a7f01431a1743
Signed-off-by: Haitao Shan <hshan@google.com>

parent dea54268

arch/x86/power/cpu.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -268,6 +268,19 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
		/* Needed by apm.c */
		void notrace restore_processor_state(void)
		{
		#ifdef __clang__
		// The following code snippet is copied from __restore_processor_state.
		// Its purpose is to prepare GS segment before the function is called.
		// Since the function is compiled with SCS on, it will use GS at its
		// entry.
		// TODO: Hack to be removed later when compiler bug is fixed.
		#ifdef CONFIG_X86_64
		wrmsrl(MSR_GS_BASE, saved_context.kernelmode_gs_base);
		#else
		loadsegment(fs, __KERNEL_PERCPU);
		loadsegment(gs, __KERNEL_STACK_CANARY);
		#endif
		#endif
		__restore_processor_state(&saved_context);
		}
		#ifdef CONFIG_X86_32