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

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Date:   Thu, 2 Nov 2017 03:56:51 -0700
From:   tip-bot for Andy Lutomirski <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, brgerst@...il.com, tglx@...utronix.de,
        hpa@...or.com, torvalds@...ux-foundation.org,
        dave.hansen@...el.com, linux-kernel@...r.kernel.org,
        mingo@...nel.org, bp@...e.de, luto@...nel.org, bpetkov@...e.de
Subject: [tip:x86/asm] x86/traps: Use a new on_thread_stack() helper to
 clean up an assertion

Commit-ID:  3383642c2f9d4f5b4fa37436db4a109a1a10018c
Gitweb:     https://git.kernel.org/tip/3383642c2f9d4f5b4fa37436db4a109a1a10018c
Author:     Andy Lutomirski <luto@...nel.org>
AuthorDate: Thu, 2 Nov 2017 00:59:17 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 2 Nov 2017 11:04:49 +0100

x86/traps: Use a new on_thread_stack() helper to clean up an assertion

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

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Borislav Petkov <bp@...e.de>
Cc: Borislav Petkov <bpetkov@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/856b15bee1f55017b8f79d3758b0d51c48a08cf8.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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 ae2ae6d..f10dae1 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 67db4f4..42a9c44 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();
 }