From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 75918C55192 for ; Thu, 23 Apr 2020 23:22:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 55D122077D for ; Thu, 23 Apr 2020 23:22:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587684165; bh=hLMKYmJyiWGannRLywh3Dp0bYs9jxWDR8ibDbApWLOg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ClWybF1RippzIrE7tTaFWCa7GgdrYyZrlrY3m20iJYorwXxyJ0i2CGMiNGuXiShme jxOvfr+Ta6nxigkzkOZN0mjHIFXrnSjYjS2EvDz9gFGqJx0l2V6DUlwp8rDISWDPJ8 8YNQ2F+i/TLxnoUmzBfRSZcD+9blDAISj5VTVBO0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729765AbgDWXWo (ORCPT ); Thu, 23 Apr 2020 19:22:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:59366 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729950AbgDWXWg (ORCPT ); Thu, 23 Apr 2020 19:22:36 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 71F7F20784; Thu, 23 Apr 2020 23:22:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587684155; bh=hLMKYmJyiWGannRLywh3Dp0bYs9jxWDR8ibDbApWLOg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kZp9z0BxBC+Bhc3rryu+K8WKqc3dDEvvZhmaHExtSmqXbEH9tDmAwqApYqlb8Xctl n5tjJRLBXerVuTIuyE2E5CZ0CJTe9MZSuHdsTGujcvh/x5zrNUNFWixRHZyHt9DyKw yzbjPudzBob66rHHVNWlJXhMCh6ukFkXwfc7sEuY= From: Sasha Levin To: linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, luto@kernel.org Cc: hpa@zytor.com, dave.hansen@intel.com, tony.luck@intel.com, ak@linux.intel.com, ravi.v.shankar@intel.com, chang.seok.bae@intel.com, Sasha Levin Subject: [PATCH v10 17/18] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Date: Thu, 23 Apr 2020 19:22:06 -0400 Message-Id: <20200423232207.5797-18-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200423232207.5797-1-sashal@kernel.org> References: <20200423232207.5797-1-sashal@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andi Kleen The kernel needs to explicitly enable FSGSBASE. So, the application needs to know if it can safely use these instructions. Just looking at the CPUID bit is not enough because it may be running in a kernel that does not enable the instructions. One way for the application would be to just try and catch the SIGILL. But that is difficult to do in libraries which may not want to overwrite the signal handlers of the main application. Enumerate the enabled FSGSBASE capability in bit 1 of AT_HWCAP2 in the ELF aux vector. AT_HWCAP2 is already used by PPC for similar purposes. The application can access it open coded or by using the getauxval() function in newer versions of glibc. Signed-off-by: Andi Kleen Signed-off-by: Chang S. Bae Reviewed-by: Tony Luck Cc: Thomas Gleixner Cc: Borislav Petkov Cc: Andy Lutomirski Cc: H. Peter Anvin Cc: Dave Hansen Cc: Tony Luck Cc: Andi Kleen Signed-off-by: Sasha Levin --- arch/x86/include/uapi/asm/hwcap2.h | 3 +++ arch/x86/kernel/cpu/common.c | 4 +++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/uapi/asm/hwcap2.h b/arch/x86/include/uapi/asm/hwcap2.h index 8b2effe6efb82..5fdfcb47000f9 100644 --- a/arch/x86/include/uapi/asm/hwcap2.h +++ b/arch/x86/include/uapi/asm/hwcap2.h @@ -5,4 +5,7 @@ /* MONITOR/MWAIT enabled in Ring 3 */ #define HWCAP2_RING3MWAIT (1 << 0) +/* Kernel allows FSGSBASE instructions available in Ring 3 */ +#define HWCAP2_FSGSBASE BIT(1) + #endif diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 0d480cbadc7dc..b5a086ea34258 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1495,8 +1495,10 @@ static void identify_cpu(struct cpuinfo_x86 *c) setup_umip(c); /* Enable FSGSBASE instructions if available. */ - if (cpu_has(c, X86_FEATURE_FSGSBASE)) + if (cpu_has(c, X86_FEATURE_FSGSBASE)) { cr4_set_bits(X86_CR4_FSGSBASE); + elf_hwcap2 |= HWCAP2_FSGSBASE; + } /* * The vendor-specific functions might have changed features. -- 2.20.1