From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751323AbdJDEAk (ORCPT ); Wed, 4 Oct 2017 00:00:40 -0400 Received: from mga07.intel.com ([134.134.136.100]:43537 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751441AbdJDDzf (ORCPT ); Tue, 3 Oct 2017 23:55:35 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.42,476,1500966000"; d="scan'208";a="906475139" 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 , "Ravi V. Shankar" , Shuah Khan , linux-kernel@vger.kernel.org, x86@kernel.org, ricardo.neri@intel.com, 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 v9 14/29] x86/insn-eval: Add utility function to get segment descriptor Date: Tue, 3 Oct 2017 20:54:17 -0700 Message-Id: <1507089272-32733-15-git-send-email-ricardo.neri-calderon@linux.intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1507089272-32733-1-git-send-email-ricardo.neri-calderon@linux.intel.com> References: <1507089272-32733-1-git-send-email-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 addresses 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 to 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 a prerequisite for functions in subsequent commits 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 | 57 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 77b48f9..d599dc3 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 #undef pr_fmt @@ -450,6 +454,59 @@ 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. + * + * Returns: + * + * Pointer to segment descriptor on success. + * + * NULL on error. + */ +static struct desc_struct *get_desc(unsigned short sel) +{ + struct desc_ptr gdt_desc = {0, 0}; + unsigned long desc_base; + +#ifdef CONFIG_MODIFY_LDT_SYSCALL + struct desc_struct *desc = NULL; + struct ldt_struct *ldt; + + 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); + ldt = current->active_mm->context.ldt; + if (ldt && sel < ldt->nr_entries) + desc = &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 memory offset of the desired descriptor + * from the base of the GDT. As bits [15:3] of the segment selector + * contain the index, it can be regarded as 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; + + return (struct desc_struct *)(gdt_desc.address + desc_base); +} + +/** * insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte * @insn: Instruction containing the ModRM byte * @regs: Register values as seen when entering kernel mode -- 2.7.4