arm64/gcs: task_gcs_el0_enable() should use passed task

Mark Rutland noticed that the task parameter is ignored and
'current' is being used instead. Since this is usually
what its passed, it hasn't yet been causing problems but likely
will as the code gets more testing.

But, once this is fixed, it creates a new bug in copy_thread_gcs()
since the gcs_el_mode isn't yet set for the task before its being
checked. Move gcs_alloc_thread_stack() after the new task's
gcs_el0_mode initialization to avoid this.

Fixes: fc84bc5 ("arm64/gcs: Context switch GCS state for EL0")
Signed-off-by: Jeremy Linton <[email protected]>
Reviewed-by: Mark Brown <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

Author: jlintonarm

arch/arm64/include/asm/gcs.h

@@ -58,7 +58,7 @@ static inline u64 gcsss2(void)
 
 static inline bool task_gcs_el0_enabled(struct task_struct *task)
 {
-	return current->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE;
+	return task->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE;
 }
 
 void gcs_set_el0_mode(struct task_struct *task);

arch/arm64/kernel/process.c

@@ -305,13 +305,13 @@ static int copy_thread_gcs(struct task_struct *p,
 	p->thread.gcs_base = 0;
 	p->thread.gcs_size = 0;
 
+	p->thread.gcs_el0_mode = current->thread.gcs_el0_mode;
+	p->thread.gcs_el0_locked = current->thread.gcs_el0_locked;
+
 	gcs = gcs_alloc_thread_stack(p, args);
 	if (IS_ERR_VALUE(gcs))
 		return PTR_ERR((void *)gcs);
 
-	p->thread.gcs_el0_mode = current->thread.gcs_el0_mode;
-	p->thread.gcs_el0_locked = current->thread.gcs_el0_locked;
-
 	return 0;
 }