From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756031AbeEaSBm (ORCPT ); Thu, 31 May 2018 14:01:42 -0400 Received: from mga01.intel.com ([192.55.52.88]:18552 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755938AbeEaR7A (ORCPT ); Thu, 31 May 2018 13:59:00 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.49,463,1520924400"; d="scan'208";a="60725518" From: "Chang S. Bae" To: Andy Lutomirski , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar Cc: Andi Kleen , Dave Hansen , Markus T Metzger , "Ravi V . Shankar" , "Chang S . Bae" , linux-kernel@vger.kernel.org Subject: [PATCH V2 07/15] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Date: Thu, 31 May 2018 10:58:37 -0700 Message-Id: <1527789525-8857-8-git-send-email-chang.seok.bae@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1527789525-8857-1-git-send-email-chang.seok.bae@intel.com> References: <1527789525-8857-1-git-send-email-chang.seok.bae@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andy Lutomirski This is temporary. It will allow the next few patches to be tested incrementally. Setting unsafe_fsgsbase is a root hole. Don't do it. Signed-off-by: Andy Lutomirski [chang: Fix the deactivated flag. Add TAINT_INSECURE flag.] Signed-off-by: Chang S. Bae Reviewed-by: Andi Kleen Cc: H. Peter Anvin Cc: Dave Hansen Cc: Thomas Gleixner Cc: Ingo Molnar --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ arch/x86/kernel/cpu/common.c | 26 +++++++++++++++++++++++++ 2 files changed, 29 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f2040d4..b92c4a0 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2600,6 +2600,9 @@ emulation library even if a 387 maths coprocessor is present. + unsafe_fsgsbase [X86] Allow FSGSBASE instructions. This will be + replaced with a nofsgsbase flag. + no_console_suspend [HW] Never suspend the console Disable suspending of consoles during suspend and diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 0be333f..5412d62 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -356,6 +356,24 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c) } /* + * Temporary hack: FSGSBASE is unsafe until a few kernel code paths are updated. + * This allows us to get the kernel ready incrementally. Setting + * unsafe_fsgsbase will allow the series to be bisected if necessary. + * + * Once all the pieces are in place, this will go away and be replaced with + * a nofsgsbase chicken flag. + */ +static bool unsafe_fsgsbase; + +static __init int setup_unsafe_fsgsbase(char *arg) +{ + unsafe_fsgsbase = true; + add_taint(TAINT_INSECURE, LOCKDEP_STILL_OK); + return 1; +} +__setup("unsafe_fsgsbase", setup_unsafe_fsgsbase); + +/* * Protection Keys are not available in 32-bit mode. */ static bool pku_disabled; @@ -1286,6 +1304,14 @@ static void identify_cpu(struct cpuinfo_x86 *c) setup_smap(c); setup_umip(c); + /* Enable FSGSBASE instructions if available. */ + if (cpu_has(c, X86_FEATURE_FSGSBASE)) { + if (unsafe_fsgsbase) + cr4_set_bits(X86_CR4_FSGSBASE); + else + clear_cpu_cap(c, X86_FEATURE_FSGSBASE); + } + /* * The vendor-specific functions might have changed features. * Now we do "generic changes." -- 2.7.4