Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751465AbcCFFxW (ORCPT ); Sun, 6 Mar 2016 00:53:22 -0500 Received: from mail.kernel.org ([198.145.29.136]:51014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751281AbcCFFwe (ORCPT ); Sun, 6 Mar 2016 00:52:34 -0500 From: Andy Lutomirski To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, Borislav Petkov , Oleg Nesterov , Andrew Cooper , Brian Gerst , Andy Lutomirski Subject: [PATCH v2 05/10] x86/traps: Clear TIF_BLOCKSTEP on all debug exceptions Date: Sat, 5 Mar 2016 21:52:18 -0800 Message-Id: X-Mailer: git-send-email 2.5.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1458 Lines: 44 The SDM says that debug exceptions clear BTF, and we need to keep TIF_BLOCKSTEP in sync with BTF. Clear it unconditionally and improve the comment. I suspect that the fact that kmemcheck could cause TIF_BLOCKSTEP not to be cleared was just an oversight. Signed-off-by: Andy Lutomirski --- arch/x86/kernel/traps.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index dd2c2e66c2e1..19e6cfa501e3 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -598,6 +598,13 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) dr6 &= ~DR6_RESERVED; /* + * The SDM says "The processor clears the BTF flag when it + * generates a debug exception." Clear TIF_BLOCKSTEP to keep + * TIF_BLOCKSTEP in sync with the hardware BTF flag. + */ + clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP); + + /* * If dr6 has no reason to give us about the origin of this trap, * then it's very likely the result of an icebp/int01 trap. * User wants a sigtrap for that. @@ -612,11 +619,6 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) /* DR6 may or may not be cleared by the CPU */ set_debugreg(0, 6); - /* - * The processor cleared BTF, so don't mark that we need it set. - */ - clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP); - /* Store the virtualized DR6 value */ tsk->thread.debugreg6 = dr6; -- 2.5.0