[PATCH v2 20/20] x86/traps: Use a new on_thread_stack() helper to clean up an assertion

[Andy Lutomirski]

Let's keep the stack-related logic together rather than open-coding
a comparison in an assertion in the traps code.

Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
 arch/x86/include/asm/processor.h | 6 ++++++
 arch/x86/kernel/traps.c          | 3 +--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index ae2ae6d80674..f10dae14f951 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -541,6 +541,12 @@ static inline unsigned long current_top_of_stack(void)
 #endif
 }
 
+static inline bool on_thread_stack(void)
+{
+	return (unsigned long)(current_top_of_stack() -
+			       current_stack_pointer) < THREAD_SIZE;
+}
+
 #ifdef CONFIG_PARAVIRT
 #include <asm/paravirt.h>
 #else
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 67db4f43309e..42a9c4458f5d 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -141,8 +141,7 @@ void ist_begin_non_atomic(struct pt_regs *regs)
 	 * will catch asm bugs and any attempt to use ist_preempt_enable
 	 * from double_fault.
 	 */
-	BUG_ON((unsigned long)(current_top_of_stack() -
-			       current_stack_pointer) >= THREAD_SIZE);
+	BUG_ON(!on_thread_stack());
 
 	preempt_enable_no_resched();
 }
-- 
2.13.6