From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752227AbbHQTW6 (ORCPT ); Mon, 17 Aug 2015 15:22:58 -0400 Received: from mail.kernel.org ([198.145.29.136]:43927 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751653AbbHQTW4 (ORCPT ); Mon, 17 Aug 2015 15:22:56 -0400 From: Andy Lutomirski To: security@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org Cc: Andy Lutomirski Subject: [PATCH 1/3] Revert "sched/x86_64: Don't save flags on context switch" Date: Mon, 17 Aug 2015 12:22:50 -0700 Message-Id: <85f56651f59f76624e80785a8fd3bdfdd089a818.1439838962.git.luto@kernel.org> X-Mailer: git-send-email 2.4.3 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 This reverts commit 2c7577a7583747c9b71f26dced7f696b739da745. It was a nice speedup. It's also not quite correct: SYSENTER enables interrupts too early. We can re-add this optimization once the SYSENTER code is beaten into shape, which should happen in 4.3 or 4.4. Cc: stable@vger.kernel.org # v3.19 Signed-off-by: Andy Lutomirski --- arch/x86/include/asm/switch_to.h | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h index 751bf4b7bf11..d7f3b3b78ac3 100644 --- a/arch/x86/include/asm/switch_to.h +++ b/arch/x86/include/asm/switch_to.h @@ -79,12 +79,12 @@ do { \ #else /* CONFIG_X86_32 */ /* frame pointer must be last for get_wchan */ -#define SAVE_CONTEXT "pushq %%rbp ; movq %%rsi,%%rbp\n\t" -#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t" +#define SAVE_CONTEXT "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t" +#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t" #define __EXTRA_CLOBBER \ , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \ - "r12", "r13", "r14", "r15", "flags" + "r12", "r13", "r14", "r15" #ifdef CONFIG_CC_STACKPROTECTOR #define __switch_canary \ @@ -100,11 +100,7 @@ do { \ #define __switch_canary_iparam #endif /* CC_STACKPROTECTOR */ -/* - * There is no need to save or restore flags, because flags are always - * clean in kernel mode, with the possible exception of IOPL. Kernel IOPL - * has no effect. - */ +/* Save restore flags to clear handle leaking NT */ #define switch_to(prev, next, last) \ asm volatile(SAVE_CONTEXT \ "movq %%rsp,%P[threadrsp](%[prev])\n\t" /* save RSP */ \ -- 2.4.3