From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757537AbbDVS1X (ORCPT ); Wed, 22 Apr 2015 14:27:23 -0400 Received: from mga11.intel.com ([192.55.52.93]:3732 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751909AbbDVS1T (ORCPT ); Wed, 22 Apr 2015 14:27:19 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,625,1422950400"; d="scan'208";a="560186449" Subject: [PATCH 01/17] x86, fpu: wrap get_xsave_addr() to make it safer To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, tglx@linutronix.de, Dave Hansen , dave.hansen@linux.intel.com, oleg@redhat.com, bp@alien8.de, riel@redhat.com, sbsiddha@gmail.com, luto@amacapital.net, mingo@redhat.com, hpa@zytor.com, fenghua.yu@intel.com From: Dave Hansen Date: Wed, 22 Apr 2015 11:27:31 -0700 References: <20150422182729.0512E57D@viggo.jf.intel.com> In-Reply-To: <20150422182729.0512E57D@viggo.jf.intel.com> Message-Id: <20150422182731.4E4F8448@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen Changes from "v19": * remove 'tsk' argument to get_xsave_addr() since the code can only realistically work on 'current', and fix up the comment a bit to match. Changes from "v17": * fix s/xstate/xsave_field/ in the function comment * remove EXPORT_SYMBOL_GPL() --- From: Dave Hansen The MPX code appears to be saving off the FPU in an unsafe way. It does not disable preemption or ensure that the FPU state has been allocated. This patch introduces a new helper which will do both of those things internally. Note that this requires a patch from Oleg in order to work properly. It is currently in tip/x86/fpu. > commit f893959b0898bd876673adbeb6798bdf25c034d7 > Author: Oleg Nesterov > Date: Fri Mar 13 18:30:30 2015 +0100 > > x86/fpu: Don't abuse drop_init_fpu() in flush_thread() Signed-off-by: Dave Hansen Cc: Oleg Nesterov Cc: bp@alien8.de Cc: Rik van Riel Cc: Suresh Siddha Cc: Andy Lutomirski Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: Fenghua Yu Cc: the arch/x86 maintainers --- b/arch/x86/include/asm/xsave.h | 1 + b/arch/x86/kernel/xsave.c | 32 ++++++++++++++++++++++++++++++++ 2 files changed, 33 insertions(+) diff -puN arch/x86/include/asm/xsave.h~tsk_get_xsave_addr arch/x86/include/asm/xsave.h --- a/arch/x86/include/asm/xsave.h~tsk_get_xsave_addr 2015-04-22 11:16:17.781800602 -0700 +++ b/arch/x86/include/asm/xsave.h 2015-04-22 11:16:17.786800827 -0700 @@ -252,6 +252,7 @@ static inline int xrestore_user(struct x } void *get_xsave_addr(struct xsave_struct *xsave, int xstate); +void *get_xsave_field(int xstate_field); void setup_xstate_comp(void); #endif diff -puN arch/x86/kernel/xsave.c~tsk_get_xsave_addr arch/x86/kernel/xsave.c --- a/arch/x86/kernel/xsave.c~tsk_get_xsave_addr 2015-04-22 11:16:17.782800647 -0700 +++ b/arch/x86/kernel/xsave.c 2015-04-22 11:16:17.786800827 -0700 @@ -741,3 +741,35 @@ void *get_xsave_addr(struct xsave_struct return (void *)xsave + xstate_comp_offsets[feature]; } EXPORT_SYMBOL_GPL(get_xsave_addr); + +/* + * This wraps up the common operations that need to occur when retrieving + * data from xsave state. It first ensures that the current task was + * using the FPU and retrieves the data in to a buffer. It then calculates + * the offset of the requested field in the buffer. + * + * This function is safe to call whether the FPU is in use or not. + * + * Note that this only works on the current task. + * + * Inputs: + * @xsave_field: state which is defined in xsave.h (e.g. XSTATE_FP, + * XSTATE_SSE, etc...) + * Output: + * address of the state in the xsave area. + */ +void *get_xsave_field(int xsave_field) +{ + union thread_xstate *xstate; + + if (!tsk_used_math(current)) + return NULL; + /* + * unlazy_fpu() is poorly named and will actually + * save the xstate off in to the memory buffer. + */ + unlazy_fpu(current); + xstate = current->thread.fpu.state; + + return get_xsave_addr(&xstate->xsave, xsave_field); +} _