From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762724AbbA3RnF (ORCPT ); Fri, 30 Jan 2015 12:43:05 -0500 Received: from mga14.intel.com ([192.55.52.115]:19408 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750927AbbA3RnD (ORCPT ); Fri, 30 Jan 2015 12:43:03 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,492,1418112000"; d="scan'208";a="678679039" Subject: [RFC][PATCH 1/2] x86, fpu: wrap get_xsave_addr() to make it safer To: oleg@redhat.com Cc: Dave Hansen , dave.hansen@linux.intel.com, riel@redhat.com, sbsiddha@gmail.com, luto@amacapital.net, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, fenghua.yu@intel.com, x86@kernel.org, linux-kernel@vger.kernel.org From: Dave Hansen Date: Fri, 30 Jan 2015 09:43:09 -0800 Message-Id: <20150130174309.D666B2A7@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 to a helper. Signed-off-by: Dave Hansen 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 Cc:linux-kernel --- 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 2015-01-30 09:42:15.457555582 -0800 +++ b/arch/x86/include/asm/xsave.h 2015-01-30 09:42:15.462555808 -0800 @@ -258,6 +258,7 @@ static inline int xrestore_user(struct x } void *get_xsave_addr(struct xsave_struct *xsave, int xstate); +void *tsk_get_xsave_field(struct task_struct *tsk, 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 2015-01-30 09:42:15.459555673 -0800 +++ b/arch/x86/kernel/xsave.c 2015-01-30 09:42:15.463555853 -0800 @@ -739,3 +739,35 @@ 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 an xsave struct. It first ensures that the task was actually + * 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. + * + * Inputs: + * tsk: the task from which we are fetching xsave state + * xstate: state which is defined in xsave.h (e.g. XSTATE_FP, XSTATE_SSE, + * etc.) + * Output: + * address of the state in the xsave area. + */ +void *tsk_get_xsave_field(struct task_struct *tsk, int xsave_field) +{ + union thread_xstate *xstate; + + unlazy_fpu(tsk); + xstate = tsk->thread.fpu.state; + /* + * This might be unallocated if the FPU + * was never in use. + */ + if (!xstate) + return NULL; + + return get_xsave_addr(&xstate->xsave, xsave_field); +} +EXPORT_SYMBOL_GPL(tsk_get_xsave_field); _