From patchwork Tue Oct 3 06:24:43 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Li, Xin3" X-Patchwork-Id: 13406888 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9F423E7542D for ; Tue, 3 Oct 2023 06:56:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239278AbjJCG4K (ORCPT ); Tue, 3 Oct 2023 02:56:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230243AbjJCGzu (ORCPT ); Tue, 3 Oct 2023 02:55:50 -0400 Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 927A9CF7; Mon, 2 Oct 2023 23:55:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1696316102; x=1727852102; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=m7R91mzhAyMwuxf88uvtu3V1UGcA6vznqDxNdL57F/c=; b=FdtT006N+CmTdugo9f0Ur8OnsM+Li+bpTa1btmxsFOOOb9e+DtqgSUAk o/jYpD04P10pQ7Ay1GFpw5urcqpoqG7YLTgXGMBwuweRwOiKzEyNoH72Q u5zjDsghgI6O8JXnLa1kC6YTW6pxLyTJGx0Vs46SK+J/FOKijSR82nUok WX4+4OwNcG7Il/1fBGz3mcmLec7zBXyWHjte3C5rLgZM2mBWxdre+/vHv eGXBicCXBH1YFKZp9bZk5hGn/OCfaVUOp/Pm3i4uMEBhnFqo+8dJSYzKo rtDUFmd7tGENHcohGYAbaEbDj12pZvmycmEA4vlAngVY2jSURvYoFwgPa w==; X-IronPort-AV: E=McAfee;i="6600,9927,10851"; a="367858169" X-IronPort-AV: E=Sophos;i="6.03,196,1694761200"; d="scan'208";a="367858169" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Oct 2023 23:54:46 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10851"; a="1081900966" X-IronPort-AV: E=Sophos;i="6.03,196,1694761200"; d="scan'208";a="1081900966" Received: from unknown (HELO fred..) ([172.25.112.68]) by fmsmga005.fm.intel.com with ESMTP; 02 Oct 2023 23:54:45 -0700 From: Xin Li To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, pbonzini@redhat.com, seanjc@google.com, peterz@infradead.org, jgross@suse.com, ravi.v.shankar@intel.com, mhiramat@kernel.org, andrew.cooper3@citrix.com, jiangshanlai@gmail.com, nik.borisov@suse.com Subject: [PATCH v12 22/37] x86/fred: Allow single-step trap and NMI when starting a new task Date: Mon, 2 Oct 2023 23:24:43 -0700 Message-Id: <20231003062458.23552-23-xin3.li@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231003062458.23552-1-xin3.li@intel.com> References: <20231003062458.23552-1-xin3.li@intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-edac@vger.kernel.org From: "H. Peter Anvin (Intel)" Entering a new task is logically speaking a return from a system call (exec, fork, clone, etc.). As such, if ptrace enables single stepping a single step exception should be allowed to trigger immediately upon entering user space. This is not optional. NMI should *never* be disabled in user space. As such, this is an optional, opportunistic way to catch errors. Allow single-step trap and NMI when starting a new task, thus once the new task enters user space, single-step trap and NMI are both enabled immediately. Signed-off-by: H. Peter Anvin (Intel) Tested-by: Shan Kang Signed-off-by: Xin Li --- Changes since v8: * Use high-order 48 bits above the lowest 16 bit SS only when FRED is enabled (Thomas Gleixner). --- arch/x86/kernel/process_64.c | 38 ++++++++++++++++++++++++++++++------ 1 file changed, 32 insertions(+), 6 deletions(-) diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 4f87f5987ae8..c075591b7b46 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -56,6 +56,7 @@ #include #include #include +#include #ifdef CONFIG_IA32_EMULATION /* Not included via unistd.h */ #include @@ -528,7 +529,7 @@ void x86_gsbase_write_task(struct task_struct *task, unsigned long gsbase) static void start_thread_common(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp, - unsigned int _cs, unsigned int _ss, unsigned int _ds) + u16 _cs, u16 _ss, u16 _ds) { WARN_ON_ONCE(regs != current_pt_regs()); @@ -545,11 +546,36 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip, loadsegment(ds, _ds); load_gs_index(0); - regs->ip = new_ip; - regs->sp = new_sp; - regs->cs = _cs; - regs->ss = _ss; - regs->flags = X86_EFLAGS_IF; + regs->ip = new_ip; + regs->sp = new_sp; + regs->csx = _cs; + regs->ssx = _ss; + /* + * Allow single-step trap and NMI when starting a new task, thus + * once the new task enters user space, single-step trap and NMI + * are both enabled immediately. + * + * Entering a new task is logically speaking a return from a + * system call (exec, fork, clone, etc.). As such, if ptrace + * enables single stepping a single step exception should be + * allowed to trigger immediately upon entering user space. + * This is not optional. + * + * NMI should *never* be disabled in user space. As such, this + * is an optional, opportunistic way to catch errors. + * + * Paranoia: High-order 48 bits above the lowest 16 bit SS are + * discarded by the legacy IRET instruction on all Intel, AMD, + * and Cyrix/Centaur/VIA CPUs, thus can be set unconditionally, + * even when FRED is not enabled. But we choose the safer side + * to use these bits only when FRED is enabled. + */ + if (cpu_feature_enabled(X86_FEATURE_FRED)) { + regs->fred_ss.swevent = true; + regs->fred_ss.nmi = true; + } + + regs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED; } void