From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752087AbbFGShF (ORCPT ); Sun, 7 Jun 2015 14:37:05 -0400 Received: from mga14.intel.com ([192.55.52.115]:19256 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751003AbbFGSgr (ORCPT ); Sun, 7 Jun 2015 14:36:47 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,569,1427785200"; d="scan'208";a="706922093" Subject: [PATCH 01/19] x86, mpx, xsave: Fix up bad get_xsave_addr() assumptions To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, tglx@linutronix.de, Dave Hansen , dave.hansen@linux.intel.com From: Dave Hansen Date: Sun, 07 Jun 2015 11:37:00 -0700 References: <20150607183700.7E78D631@viggo.jf.intel.com> In-Reply-To: <20150607183700.7E78D631@viggo.jf.intel.com> Message-Id: <20150607183700.1E739B34@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen get_xsave_addr() assumes that if an xsave bit is present in the hardware (pcntxt_mask) that it is present in a given xsave buffer. Due to an bug in the xsave code on all of the systems that have MPX (and thus all the users of this code), that has been a true assumption. But, the bug is getting fixed, so our assumption is not going to hold any more. It's quite possible (and normal) for an enabled state to be present on 'pcntxt_mask', but *not* in 'xstate_bv'. We need to consult 'xstate_bv'. Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner --- b/arch/x86/kernel/fpu/xstate.c | 45 +++++++++++++++++++++++++++++++++-------- 1 file changed, 37 insertions(+), 8 deletions(-) diff -puN arch/x86/kernel/fpu/xstate.c~consullt-xstate_bv arch/x86/kernel/fpu/xstate.c --- a/arch/x86/kernel/fpu/xstate.c~consullt-xstate_bv 2015-06-01 10:24:03.025676699 -0700 +++ b/arch/x86/kernel/fpu/xstate.c 2015-06-01 10:24:03.029676880 -0700 @@ -382,19 +382,48 @@ void fpu__resume_cpu(void) * This is the API that is called to get xstate address in either * standard format or compacted format of xsave area. * + * Note that if there is no data for the field in the xsave buffer + * this will return NULL. + * * Inputs: - * xsave: base address of the xsave area; - * xstate: state which is defined in xsave.h (e.g. XSTATE_FP, XSTATE_SSE, - * etc.) + * xstate: the thread's storage area for all FPU data + * xstate_feature: state which is defined in xsave.h (e.g. + * XSTATE_FP, XSTATE_SSE, etc...) * Output: - * address of the state in the xsave area. + * address of the state in the xsave area, or NULL if the + * field is not present in the xsave buffer. */ -void *get_xsave_addr(struct xregs_state *xsave, int xstate) +void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature) { - int feature = fls64(xstate) - 1; - if (!test_bit(feature, (unsigned long *)&xfeatures_mask)) + int feature_nr = fls64(xstate_feature) - 1; + /* + * Do we even *have* xsave state? + */ + if (!boot_cpu_has(X86_FEATURE_XSAVE)) + return NULL; + + xsave = ¤t->thread.fpu.state.xsave; + /* + * We should not ever be requesting features that we + * have not enabled. Remember that pcntxt_mask is + * what we write to the XCR0 register. + */ + WARN_ONCE(!(xfeatures_mask & xstate_feature), + "get of unsupported state"); + /* + * This assumes the last 'xsave*' instruction to + * have requested that 'xstate_feature' be saved. + * If it did not, we might be seeing and old value + * of the field in the buffer. + * + * This can happen because the last 'xsave' did not + * request that this feature be saved (unlikely) + * or because the "init optimization" caused it + * to not be saved. + */ + if (!(xsave->header.xfeatures & xstate_feature)) return NULL; - return (void *)xsave + xstate_comp_offsets[feature]; + return (void *)xsave + xstate_comp_offsets[feature_nr]; } EXPORT_SYMBOL_GPL(get_xsave_addr); _