From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932437AbbEHTFE (ORCPT ); Fri, 8 May 2015 15:05:04 -0400 Received: from mga03.intel.com ([134.134.136.65]:24923 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753032AbbEHS7f (ORCPT ); Fri, 8 May 2015 14:59:35 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,391,1427785200"; d="scan'208";a="491194265" 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: Fri, 08 May 2015 11:59:48 -0700 References: <20150508185948.4C19F4B0@viggo.jf.intel.com> In-Reply-To: <20150508185948.4C19F4B0@viggo.jf.intel.com> Message-Id: <20150508185948.01B91DEB@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 --- b/arch/x86/kernel/xsave.c | 41 ++++++++++++++++++++++++++++++++++------- 1 file changed, 34 insertions(+), 7 deletions(-) diff -puN arch/x86/kernel/xsave.c~consullt-xstate_bv arch/x86/kernel/xsave.c --- a/arch/x86/kernel/xsave.c~consullt-xstate_bv 2015-05-08 11:46:10.595563814 -0700 +++ b/arch/x86/kernel/xsave.c 2015-05-08 11:46:10.598563949 -0700 @@ -706,19 +706,46 @@ void __init_refok eager_fpu_init(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_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_addr(struct xsave_struct *xsave, int xstate) +void *get_xsave_addr(struct xsave_struct *xsave, int xstate_field) { - int feature = fls64(xstate) - 1; - if (!test_bit(feature, (unsigned long *)&pcntxt_mask)) + int feature_nr = fls64(xstate_field) - 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 fields that we + * have not enabled. Remember that pcntxt_mask is + * what we write to the XCR0 register. + */ + WARN_ONCE(!(pcntxt_mask & xstate_field), "get of unsupported state"); + /* + * This assumes the last 'xsave*' instruction to + * have requested that 'xstate_field' 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->xsave_hdr.xstate_bv & xstate_field)) return NULL; - return (void *)xsave + xstate_comp_offsets[feature]; + return (void *)xsave + xstate_comp_offsets[feature_nr]; } EXPORT_SYMBOL_GPL(get_xsave_addr); _