scs: Move scs_overflow_check() out of architecture code

There is nothing architecture-specific about scs_overflow_check() as
it's just a trivial wrapper around scs_corrupted().

For parity with task_stack_end_corrupted(), rename scs_corrupted() to
task_scs_end_corrupted() and call it from schedule_debug() when
CONFIG_SCHED_STACK_END_CHECK_is enabled, which better reflects its
purpose as a debug feature to catch inadvertent overflow of the SCS.
Finally, remove the unused scs_overflow_check() function entirely.

This has absolutely no impact on architectures that do not support SCS
(currently arm64 only).
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/scs.h

@@ -24,24 +24,6 @@
 	.endm
 #endif /* CONFIG_SHADOW_CALL_STACK */
 
-#else /* __ASSEMBLY__ */
-
-#include <linux/scs.h>
-
-#ifdef CONFIG_SHADOW_CALL_STACK
-
-static inline void scs_overflow_check(struct task_struct *tsk)
-{
-	if (unlikely(scs_corrupted(tsk)))
-		panic("corrupted shadow stack detected inside scheduler\n");
-}
-
-#else /* CONFIG_SHADOW_CALL_STACK */
-
-static inline void scs_overflow_check(struct task_struct *tsk) {}
-
-#endif /* CONFIG_SHADOW_CALL_STACK */
-
 #endif /* __ASSEMBLY __ */
 
 #endif /* _ASM_SCS_H */

arch/arm64/kernel/process.c

@@ -52,7 +52,6 @@
 #include <asm/mmu_context.h>
 #include <asm/processor.h>
 #include <asm/pointer_auth.h>
-#include <asm/scs.h>
 #include <asm/stacktrace.h>
 
 #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
@@ -516,7 +515,6 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	entry_task_switch(next);
 	uao_thread_switch(next);
 	ssbs_thread_switch(next);
-	scs_overflow_check(next);
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case

arch/arm64/kernel/scs.c

@@ -6,7 +6,7 @@
  */
 
 #include <linux/percpu.h>
-#include <asm/scs.h>
+#include <linux/scs.h>
 
 /* Allocate a static per-CPU shadow stack */
 #define DEFINE_SCS(name)						\

include/linux/scs.h

@@ -47,7 +47,7 @@ static inline unsigned long *__scs_magic(void *s)
 	return (unsigned long *)(s + SCS_SIZE) - 1;
 }
 
-static inline bool scs_corrupted(struct task_struct *tsk)
+static inline bool task_scs_end_corrupted(struct task_struct *tsk)
 {
 	unsigned long *magic = __scs_magic(task_scs(tsk));
 	unsigned long sz = task_scs_sp(tsk) - task_scs(tsk);
@@ -60,8 +60,8 @@ static inline bool scs_corrupted(struct task_struct *tsk)
 static inline void scs_init(void) {}
 static inline void scs_task_reset(struct task_struct *tsk) {}
 static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }
-static inline bool scs_corrupted(struct task_struct *tsk) { return false; }
 static inline void scs_release(struct task_struct *tsk) {}
+static inline bool task_scs_end_corrupted(struct task_struct *tsk) { return false; }
 
 #endif /* CONFIG_SHADOW_CALL_STACK */
 

kernel/sched/core.c

@@ -3878,6 +3878,9 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
 #ifdef CONFIG_SCHED_STACK_END_CHECK
 	if (task_stack_end_corrupted(prev))
 		panic("corrupted stack end detected inside scheduler\n");
+
+	if (task_scs_end_corrupted(prev))
+		panic("corrupted shadow stack detected inside scheduler\n");
 #endif
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP

kernel/scs.c

@@ -98,7 +98,8 @@ void scs_release(struct task_struct *tsk)
 	if (!s)
 		return;
 
-	WARN(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
+	WARN(task_scs_end_corrupted(tsk),
+	     "corrupted shadow stack detected when freeing task\n");
 	scs_check_usage(tsk);
 	scs_free(s);
 }