From patchwork Tue Dec 5 10:50:09 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Li, Xin3" X-Patchwork-Id: 13480039 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="bSXS6L4r" Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.12]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D2ED5191; Tue, 5 Dec 2023 03:21:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1701775291; x=1733311291; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=g+1BPOHGWOCmAN2ihj8vafw+Z+qq/YZJt19PCQv0I50=; b=bSXS6L4rRWoTVSOpcVap6XvNVoD8BW+aww5jAQrZ4tiqKRGLeeGftAzo I/j9hA2wBEdmgwWCpO/T3esiw3qHr+mywJlnULjh9WMlNmwwvlwfL16sS 5xPrZB4UM7dOgCUGFkmLx7xhBBS2Cy/PsDdEYTeAcU4yppRzql9vqDaJz JOhyvs1tZeiUJi4d/AqTGsJbrCezCOXayyop6c3yycL6YYTRKopdBmX1J lsYZjXMpFGLjZytjJuKHF7mk5WJbJ0averYf6g71Xef2/+w5sVMYUbbOj Tuo+gwW/oBX8VsNfgMPweYAIDv9X2JLnoePmWRibL6ASeQPuZfPEEYXnI Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10914"; a="942543" X-IronPort-AV: E=Sophos;i="6.04,252,1695711600"; d="scan'208";a="942543" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Dec 2023 03:21:23 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10914"; a="1018192968" X-IronPort-AV: E=Sophos;i="6.04,252,1695711600"; d="scan'208";a="1018192968" Received: from unknown (HELO fred..) ([172.25.112.68]) by fmsmga006.fm.intel.com with ESMTP; 05 Dec 2023 03:21:22 -0800 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, shan.kang@intel.com Subject: [PATCH v13 20/35] x86/fred: Allow single-step trap and NMI when starting a new task Date: Tue, 5 Dec 2023 02:50:09 -0800 Message-ID: <20231205105030.8698-21-xin3.li@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231205105030.8698-1-xin3.li@intel.com> References: <20231205105030.8698-1-xin3.li@intel.com> Precedence: bulk X-Mailing-List: linux-edac@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 7f66c0b14de6..7062b84dd467 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