linux-kernel - [RFC 17/17] x86/traps: Use a new on_thread_stack() helper to clean up an assertion

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Date:   Wed,  6 Sep 2017 14:37:02 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [RFC 17/17] x86/traps: Use a new on_thread_stack() helper to clean up an assertion

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/processor.h   | 17 +++++++++++++++++
 arch/x86/include/asm/thread_info.h | 11 -----------
 arch/x86/kernel/traps.c            |  3 +--
 3 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 4c137472f530..b6f8dc11c222 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -534,6 +534,23 @@ static inline unsigned long current_top_of_stack(void)
 #endif
 }
 
+static inline unsigned long current_stack_pointer(void)
+{
+	unsigned long sp;
+#ifdef CONFIG_X86_64
+	asm("mov %%rsp,%0" : "=g" (sp));
+#else
+	asm("mov %%esp,%0" : "=g" (sp));
+#endif
+	return sp;
+}
+
+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/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index e00e1bd6e7b3..90e1f9b84534 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -155,17 +155,6 @@ struct thread_info {
  */
 #ifndef __ASSEMBLY__
 
-static inline unsigned long current_stack_pointer(void)
-{
-	unsigned long sp;
-#ifdef CONFIG_X86_64
-	asm("mov %%rsp,%0" : "=g" (sp));
-#else
-	asm("mov %%esp,%0" : "=g" (sp));
-#endif
-	return sp;
-}
-
 /*
  * Walks up the stack frames to make sure that the specified object is
  * entirely contained by a single stack frame.
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index bf54309b85da..0347ed41c92d 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -153,8 +153,7 @@ 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();
 }
-- 
2.13.5