From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753234AbdEESUA (ORCPT ); Fri, 5 May 2017 14:20:00 -0400 Received: from mga07.intel.com ([134.134.136.100]:40575 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751736AbdEESSI (ORCPT ); Fri, 5 May 2017 14:18:08 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.38,293,1491289200"; d="scan'208";a="96140783" From: Ricardo Neri To: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov Cc: Peter Zijlstra , Andrew Morton , Brian Gerst , Chris Metcalf , Dave Hansen , Paolo Bonzini , Liang Z Li , Masami Hiramatsu , Huang Rui , Jiri Slaby , Jonathan Corbet , "Michael S. Tsirkin" , Paul Gortmaker , Vlastimil Babka , Chen Yucong , Alexandre Julliard , Stas Sergeev , Fenghua Yu , "Ravi V. Shankar" , Shuah Khan , linux-kernel@vger.kernel.org, x86@kernel.org, linux-msdos@vger.kernel.org, wine-devel@winehq.org, Ricardo Neri , Adam Buchbinder , Colin Ian King , Lorenzo Stoakes , Qiaowei Ren , Arnaldo Carvalho de Melo , Adrian Hunter , Kees Cook , Thomas Garnier , Dmitry Vyukov Subject: [PATCH v7 11/26] x86/insn-eval: Add utility function to get segment descriptor Date: Fri, 5 May 2017 11:17:09 -0700 Message-Id: <20170505181724.55000-12-ricardo.neri-calderon@linux.intel.com> X-Mailer: git-send-email 2.9.3 In-Reply-To: <20170505181724.55000-1-ricardo.neri-calderon@linux.intel.com> References: <20170505181724.55000-1-ricardo.neri-calderon@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The segment descriptor contains information that is relevant to how linear address need to be computed. It contains the default size of addresses as well as the base address of the segment. Thus, given a segment selector, we ought look at segment descriptor to correctly calculate the linear address. In protected mode, the segment selector might indicate a segment descriptor from either the global descriptor table or a local descriptor table. Both cases are considered in this function. This function is the initial implementation for subsequent functions that will obtain the aforementioned attributes of the segment descriptor. Cc: Dave Hansen Cc: Adam Buchbinder Cc: Colin Ian King Cc: Lorenzo Stoakes Cc: Qiaowei Ren Cc: Arnaldo Carvalho de Melo Cc: Masami Hiramatsu Cc: Adrian Hunter Cc: Kees Cook Cc: Thomas Garnier Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Dmitry Vyukov Cc: Ravi V. Shankar Cc: x86@kernel.org Signed-off-by: Ricardo Neri --- arch/x86/lib/insn-eval.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 0a496f4..f46cb31 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -6,9 +6,13 @@ #include #include #include +#include +#include +#include #include #include #include +#include #include enum reg_type { @@ -421,6 +425,57 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, } /** + * get_desc() - Obtain address of segment descriptor + * @sel: Segment selector + * + * Given a segment selector, obtain a pointer to the segment descriptor. + * Both global and local descriptor tables are supported. + * + * Return: pointer to segment descriptor on success. NULL on failure. + */ +static struct desc_struct *get_desc(unsigned short sel) +{ + struct desc_ptr gdt_desc = {0, 0}; + struct desc_struct *desc = NULL; + unsigned long desc_base; + +#ifdef CONFIG_MODIFY_LDT_SYSCALL + if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) { + /* Bits [15:3] contain the index of the desired entry. */ + sel >>= 3; + + mutex_lock(¤t->active_mm->context.lock); + /* The size of the LDT refers to the number of entries. */ + if (!current->active_mm->context.ldt || + sel >= current->active_mm->context.ldt->size) { + mutex_unlock(¤t->active_mm->context.lock); + return NULL; + } + + desc = ¤t->active_mm->context.ldt->entries[sel]; + mutex_unlock(¤t->active_mm->context.lock); + return desc; + } +#endif + native_store_gdt(&gdt_desc); + + /* + * Segment descriptors have a size of 8 bytes. Thus, the index is + * multiplied by 8 to obtain the offset of the desired descriptor from + * the start of the GDT. As bits [15:3] of the segment selector contain + * the index, it can be regarded multiplied by 8 already. All that + * remains is to clear bits [2:0]. + */ + desc_base = sel & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK); + + if (desc_base > gdt_desc.size) + return NULL; + + desc = (struct desc_struct *)(gdt_desc.address + desc_base); + return desc; +} + +/** * insn_get_reg_offset_modrm_rm() - Obtain register in r/m part of ModRM byte * @insn: Instruction structure containing the ModRM byte * @regs: Structure with register values as seen when entering kernel mode -- 2.9.3