From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757301AbbFPUR6 (ORCPT ); Tue, 16 Jun 2015 16:17:58 -0400 Received: from mail.kernel.org ([198.145.29.136]:42560 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756978AbbFPURO (ORCPT ); Tue, 16 Jun 2015 16:17:14 -0400 From: Andy Lutomirski To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Weisbecker?= , Rik van Riel , Oleg Nesterov , Denys Vlasenko , Borislav Petkov , Kees Cook , Brian Gerst , Andy Lutomirski Subject: [RFC/INCOMPLETE 05/13] x86/entry: Add enter_from_user_mode and use it in syscalls Date: Tue, 16 Jun 2015 13:16:51 -0700 Message-Id: <68824568658cb82bca5c2a7a2d171068c3df045d.1434485184.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 Changing the x86 context tracking hooks is dangerous because there are no good checks that we track our context correctly. Add a helper to check that we're actually in CONTEXT_USER when we enter from user mode and wire it up for syscall entries. Subsequent patches will wire this up for all non-NMI entries as well. NMIs are their own special beast and cannot currently switch overall context tracking state. Instead, they have their own special RCU hooks. This is a tiny speedup if !CONFIG_CONTEXT_TRACKING (removes a branch) and a tiny slowdown if CONFIG_CONTEXT_TRACING (adds a layer of indirection). Eventually, we should fix up the core context tracking code to supply a function that does what we want (and can be much simpler than user_exit), which will enable us to get rid of the extra call. Signed-off-by: Andy Lutomirski --- arch/x86/entry/common.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 348465473e55..54af0df50080 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -28,6 +28,15 @@ #define CREATE_TRACE_POINTS #include +#ifdef CONFIG_CONTEXT_TRACKING +/* Called on entry from user mode with IRQs off. */ +asmlinkage __visible void enter_from_user_mode(void) +{ + context_tracking_assert_state(CONTEXT_USER); + user_exit(); +} +#endif + static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) { #ifdef CONFIG_X86_64 @@ -65,14 +74,16 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch) work = ACCESS_ONCE(current_thread_info()->flags) & _TIF_WORK_SYSCALL_ENTRY; +#ifdef CONFIG_CONTEXT_TRACKING /* * If TIF_NOHZ is set, we are required to call user_exit() before * doing anything that could touch RCU. */ if (work & _TIF_NOHZ) { - user_exit(); + enter_from_user_mode(); work &= ~_TIF_NOHZ; } +#endif #ifdef CONFIG_SECCOMP /* -- 2.4.3