From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753423AbbCWTKZ (ORCPT ); Mon, 23 Mar 2015 15:10:25 -0400 Received: from mail.kernel.org ([198.145.29.136]:56025 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752465AbbCWTKV (ORCPT ); Mon, 23 Mar 2015 15:10:21 -0400 From: Andy Lutomirski To: Takashi Iwai , Denys Vlasenko , Stefan Seyfried , X86 ML Cc: Jiri Kosina , LKML , Tejun Heo , Andy Lutomirski Subject: [PATCH] x86, entry: Check for syscall exit work with IRQs disabled Date: Mon, 23 Mar 2015 12:10:18 -0700 Message-Id: <189320d42b4d671df78c10555976bb10af1ffc75.1427137498.git.luto@kernel.org> X-Mailer: git-send-email 2.3.0 In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We currently have a race: if we're preempted during syscall exit, we can fail to process syscall return work that is queued up while we're preempted in ret_from_sys_call after checking ti.flags. Fix it by disabling interrupts before checking ti.flags. Fixes: 96b6352c1271 x86_64, entry: Remove the syscall exit audit and schedule optimizations Reported-by: Stefan Seyfried Reported-by: Takashi Iwai Signed-off-by: Andy Lutomirski --- Ingo, I don't understand the LOCKDEP_SYS_EXIT stuff. Can you take a quick look to confirm that it's okay to call it more than once? arch/x86/kernel/entry_64.S | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 1d74d161687c..2babb393915e 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -364,12 +364,21 @@ system_call_fastpath: * Has incomplete stack frame and undefined top of stack. */ ret_from_sys_call: - testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) - jnz int_ret_from_sys_call_fixup /* Go the the slow path */ - LOCKDEP_SYS_EXIT DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF + + /* + * We must check ti flags with interrupts (or at least preemption) + * off because we must *never* return to userspace without + * processing exit work that is enqueued if we're preempted here. + * In particular, returning to userspace with any of the one-shot + * flags (TIF_NOTIFY_RESUME, TIF_USER_RETURN_NOTIFY, etc) set is + * very bad. + */ + testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) + jnz int_ret_from_sys_call_fixup /* Go the the slow path */ + CFI_REMEMBER_STATE /* * sysretq will re-enable interrupts: @@ -386,7 +395,7 @@ ret_from_sys_call: int_ret_from_sys_call_fixup: FIXUP_TOP_OF_STACK %r11, -ARGOFFSET - jmp int_ret_from_sys_call + jmp int_ret_from_sys_call_irqs_off /* Do syscall tracing */ tracesys: @@ -432,6 +441,7 @@ tracesys_phase2: GLOBAL(int_ret_from_sys_call) DISABLE_INTERRUPTS(CLBR_NONE) TRACE_IRQS_OFF +int_ret_from_sys_call_irqs_off: movl $_TIF_ALLWORK_MASK,%edi /* edi: mask to check */ GLOBAL(int_with_check) -- 2.3.0