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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 91B7EC433F4 for ; Tue, 18 Sep 2018 23:10:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5379121471 for ; Tue, 18 Sep 2018 23:10:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5379121471 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728219AbeISEob (ORCPT ); Wed, 19 Sep 2018 00:44:31 -0400 Received: from mga14.intel.com ([192.55.52.115]:3122 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725873AbeISEob (ORCPT ); Wed, 19 Sep 2018 00:44:31 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Sep 2018 16:09:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,391,1531810800"; d="scan'208";a="87288046" Received: from chang-linux-2.sc.intel.com ([10.3.52.139]) by fmsmga002.fm.intel.com with ESMTP; 18 Sep 2018 16:09:39 -0700 From: "Chang S. Bae" To: Ingo Molnar , Thomas Gleixner , Andy Lutomirski , "H . Peter Anvin" Cc: Andi Kleen , Dave Hansen , Markus T Metzger , Ravi Shankar , "Chang S . Bae" , LKML Subject: [PATCH v6 1/8] x86/arch_prctl/64: Make ptrace read FS/GS base accurately Date: Tue, 18 Sep 2018 16:08:52 -0700 Message-Id: <1537312139-5580-2-git-send-email-chang.seok.bae@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1537312139-5580-1-git-send-email-chang.seok.bae@intel.com> References: <1537312139-5580-1-git-send-email-chang.seok.bae@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andy Lutomirski Ptrace can read FS/GS base using the register access API (PTRACE_PEEKUSER, etc) or PTRACE_ARCH_PRCTL. Make both of these mechanisms return the actual FS/GS base. This will improve debuggability by providing the correct information to ptracer (GDB and etc). Signed-off-by: Andy Lutomirski [chang: Rebase and revise patch description] Signed-off-by: Chang S. Bae Reviewed-by: Andi Kleen Cc: H. Peter Anvin Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Dave Hansen --- arch/x86/kernel/ptrace.c | 62 ++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 52 insertions(+), 10 deletions(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index e2ee403..3acbf45 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -39,6 +39,7 @@ #include #include #include +#include #include "tls.h" @@ -342,6 +343,49 @@ static int set_segment_reg(struct task_struct *task, return 0; } +static unsigned long task_seg_base(struct task_struct *task, + unsigned short selector) +{ + unsigned short idx = selector >> 3; + unsigned long base; + + if (likely((selector & SEGMENT_TI_MASK) == 0)) { + if (unlikely(idx >= GDT_ENTRIES)) + return 0; + + /* + * There are no user segments in the GDT with nonzero bases + * other than the TLS segments. + */ + if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) + return 0; + + idx -= GDT_ENTRY_TLS_MIN; + base = get_desc_base(&task->thread.tls_array[idx]); + } else { +#ifdef CONFIG_MODIFY_LDT_SYSCALL + struct ldt_struct *ldt; + + /* + * If performance here mattered, we could protect the LDT + * with RCU. This is a slow path, though, so we can just + * take the mutex. + */ + mutex_lock(&task->mm->context.lock); + ldt = task->mm->context.ldt; + if (unlikely(idx >= ldt->nr_entries)) + base = 0; + else + base = get_desc_base(ldt->entries + idx); + mutex_unlock(&task->mm->context.lock); +#else + base = 0; +#endif + } + + return base; +} + #endif /* CONFIG_X86_32 */ static unsigned long get_flags(struct task_struct *task) @@ -435,18 +479,16 @@ static unsigned long getreg(struct task_struct *task, unsigned long offset) #ifdef CONFIG_X86_64 case offsetof(struct user_regs_struct, fs_base): { - /* - * XXX: This will not behave as expected if called on - * current or if fsindex != 0. - */ - return task->thread.fsbase; + if (task->thread.fsindex == 0) + return task->thread.fsbase; + else + return task_seg_base(task, task->thread.fsindex); } case offsetof(struct user_regs_struct, gs_base): { - /* - * XXX: This will not behave as expected if called on - * current or if fsindex != 0. - */ - return task->thread.gsbase; + if (task->thread.gsindex == 0) + return task->thread.gsbase; + else + return task_seg_base(task, task->thread.gsindex); } #endif } -- 2.7.4