From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755410AbdKAVHI (ORCPT ); Wed, 1 Nov 2017 17:07:08 -0400 Received: from terminus.zytor.com ([65.50.211.136]:50219 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755305AbdKAVHF (ORCPT ); Wed, 1 Nov 2017 17:07:05 -0400 Date: Wed, 1 Nov 2017 14:00:05 -0700 From: tip-bot for Ricardo Neri Message-ID: Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, cmetcalf@mellanox.com, colin.king@canonical.com, adrian.hunter@intel.com, shuah@kernel.org, corbet@lwn.net, adam.buchbinder@gmail.com, luto@kernel.org, mingo@kernel.org, dvyukov@google.com, brgerst@gmail.com, ravi.v.shankar@intel.com, bp@suse.de, tglx@linutronix.de, paul.gortmaker@windriver.com, ray.huang@amd.com, dave.hansen@linux.intel.com, thgarnie@google.com, peterz@infradead.org, qiaowei.ren@intel.com, ricardo.neri-calderon@linux.intel.com, keescook@chromium.org, pbonzini@redhat.com, vbabka@suse.cz, slaoub@gmail.com, mst@redhat.com, acme@redhat.com, mhiramat@kernel.org, hpa@zytor.com, lstoakes@gmail.com, jslaby@suse.cz Reply-To: shuah@kernel.org, adrian.hunter@intel.com, akpm@linux-foundation.org, cmetcalf@mellanox.com, colin.king@canonical.com, linux-kernel@vger.kernel.org, ravi.v.shankar@intel.com, mingo@kernel.org, dvyukov@google.com, brgerst@gmail.com, luto@kernel.org, corbet@lwn.net, adam.buchbinder@gmail.com, thgarnie@google.com, peterz@infradead.org, dave.hansen@linux.intel.com, tglx@linutronix.de, paul.gortmaker@windriver.com, ray.huang@amd.com, bp@suse.de, jslaby@suse.cz, mst@redhat.com, acme@redhat.com, mhiramat@kernel.org, hpa@zytor.com, lstoakes@gmail.com, slaoub@gmail.com, vbabka@suse.cz, ricardo.neri-calderon@linux.intel.com, qiaowei.ren@intel.com, keescook@chromium.org, pbonzini@redhat.com In-Reply-To: <1509135945-13762-14-git-send-email-ricardo.neri-calderon@linux.intel.com> References: <1509135945-13762-14-git-send-email-ricardo.neri-calderon@linux.intel.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/mpx] x86/insn-eval: Add utility functions to get segment selector Git-Commit-ID: 32d0b95300db03c2b23b2ea2c94769a4a138e79d X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 32d0b95300db03c2b23b2ea2c94769a4a138e79d Gitweb: https://git.kernel.org/tip/32d0b95300db03c2b23b2ea2c94769a4a138e79d Author: Ricardo Neri AuthorDate: Fri, 27 Oct 2017 13:25:40 -0700 Committer: Thomas Gleixner CommitDate: Wed, 1 Nov 2017 21:50:11 +0100 x86/insn-eval: Add utility functions to get segment selector When computing a linear address and segmentation is used, we need to know the base address of the segment involved in the computation. In most of the cases, the segment base address will be zero as in USER_DS/USER32_DS. However, it may be possible that a user space program defines its own segments via a local descriptor table. In such a case, the segment base address may not be zero. Thus, the segment base address is needed to calculate correctly the linear address. If running in protected mode, the segment selector to be used when computing a linear address is determined by either any of segment override prefixes in the instruction or inferred from the registers involved in the computation of the effective address; in that order. Also, there are cases when the segment override prefixes shall be ignored (i.e., code segments are always selected by the CS segment register; string instructions always use the ES segment register when using rDI register as operand). In long mode, segment registers are ignored, except for FS and GS. In these two cases, base addresses are obtained from the respective MSRs. For clarity, this process can be split into four steps (and an equal number of functions): determine if segment prefixes overrides can be used; parse the segment override prefixes, and use them if found; if not found or cannot be used, use the default segment registers associated with the operand registers. Once the segment register to use has been identified, read its value to obtain the segment selector. The method to obtain the segment selector depends on several factors. In 32-bit builds, segment selectors are saved into a pt_regs structure when switching to kernel mode. The same is also true for virtual-8086 mode. In 64-bit builds, segmentation is mostly ignored, except when running a program in 32-bit legacy mode. In this case, CS and SS can be obtained from pt_regs. DS, ES, FS and GS can be read directly from the respective segment registers. In order to identify the segment registers, a new set of #defines is introduced. It also includes two special identifiers. One of them indicates when the default segment register associated with instruction operands shall be used. Another one indicates that the contents of the segment register shall be ignored; this identifier is used when in long mode. Improvements-by: Borislav Petkov Signed-off-by: Ricardo Neri Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: "Michael S. Tsirkin" Cc: Peter Zijlstra Cc: Dave Hansen Cc: ricardo.neri@intel.com Cc: Adrian Hunter Cc: Paul Gortmaker Cc: Huang Rui Cc: Qiaowei Ren Cc: Shuah Khan Cc: Kees Cook Cc: Jonathan Corbet Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: "Ravi V. Shankar" Cc: Chris Metcalf Cc: Brian Gerst Cc: Arnaldo Carvalho de Melo Cc: Andy Lutomirski Cc: Colin Ian King Cc: Chen Yucong Cc: Adam Buchbinder Cc: Vlastimil Babka Cc: Lorenzo Stoakes Cc: Masami Hiramatsu Cc: Paolo Bonzini Cc: Andrew Morton Cc: Thomas Garnier Link: https://lkml.kernel.org/r/1509135945-13762-14-git-send-email-ricardo.neri-calderon@linux.intel.com --- arch/x86/include/asm/inat.h | 10 ++ arch/x86/lib/insn-eval.c | 340 ++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 350 insertions(+) diff --git a/arch/x86/include/asm/inat.h b/arch/x86/include/asm/inat.h index 02aff08..1c78580 100644 --- a/arch/x86/include/asm/inat.h +++ b/arch/x86/include/asm/inat.h @@ -97,6 +97,16 @@ #define INAT_MAKE_GROUP(grp) ((grp << INAT_GRP_OFFS) | INAT_MODRM) #define INAT_MAKE_IMM(imm) (imm << INAT_IMM_OFFS) +/* Identifiers for segment registers */ +#define INAT_SEG_REG_IGNORE 0 +#define INAT_SEG_REG_DEFAULT 1 +#define INAT_SEG_REG_CS 2 +#define INAT_SEG_REG_SS 3 +#define INAT_SEG_REG_DS 4 +#define INAT_SEG_REG_ES 5 +#define INAT_SEG_REG_FS 6 +#define INAT_SEG_REG_GS 7 + /* Attribute search APIs */ extern insn_attr_t inat_get_opcode_attribute(insn_byte_t opcode); extern int inat_get_last_prefix_id(insn_byte_t last_pfx); diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index ac7b87c..6a902b1 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -9,6 +9,7 @@ #include #include #include +#include #undef pr_fmt #define pr_fmt(fmt) "insn: " fmt @@ -47,6 +48,345 @@ static bool is_string_insn(struct insn *insn) } } +/** + * get_seg_reg_override_idx() - obtain segment register override index + * @insn: Valid instruction with segment override prefixes + * + * Inspect the instruction prefixes in @insn and find segment overrides, if any. + * + * Returns: + * + * A constant identifying the segment register to use, among CS, SS, DS, + * ES, FS, or GS. INAT_SEG_REG_DEFAULT is returned if no segment override + * prefixes were found. + * + * -EINVAL in case of error. + */ +static int get_seg_reg_override_idx(struct insn *insn) +{ + int idx = INAT_SEG_REG_DEFAULT; + int num_overrides = 0, i; + + insn_get_prefixes(insn); + + /* Look for any segment override prefixes. */ + for (i = 0; i < insn->prefixes.nbytes; i++) { + insn_attr_t attr; + + attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]); + switch (attr) { + case INAT_MAKE_PREFIX(INAT_PFX_CS): + idx = INAT_SEG_REG_CS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_SS): + idx = INAT_SEG_REG_SS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_DS): + idx = INAT_SEG_REG_DS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_ES): + idx = INAT_SEG_REG_ES; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_FS): + idx = INAT_SEG_REG_FS; + num_overrides++; + break; + case INAT_MAKE_PREFIX(INAT_PFX_GS): + idx = INAT_SEG_REG_GS; + num_overrides++; + break; + /* No default action needed. */ + } + } + + /* More than one segment override prefix leads to undefined behavior. */ + if (num_overrides > 1) + return -EINVAL; + + return idx; +} + +/** + * check_seg_overrides() - check if segment override prefixes are allowed + * @insn: Valid instruction with segment override prefixes + * @regoff: Operand offset, in pt_regs, for which the check is performed + * + * For a particular register used in register-indirect addressing, determine if + * segment override prefixes can be used. Specifically, no overrides are allowed + * for rDI if used with a string instruction. + * + * Returns: + * + * True if segment override prefixes can be used with the register indicated + * in @regoff. False if otherwise. + */ +static bool check_seg_overrides(struct insn *insn, int regoff) +{ + if (regoff == offsetof(struct pt_regs, di) && is_string_insn(insn)) + return false; + + return true; +} + +/** + * resolve_default_seg() - resolve default segment register index for an operand + * @insn: Instruction with opcode and address size. Must be valid. + * @regs: Register values as seen when entering kernel mode + * @off: Operand offset, in pt_regs, for which resolution is needed + * + * Resolve the default segment register index associated with the instruction + * operand register indicated by @off. Such index is resolved based on defaults + * described in the Intel Software Development Manual. + * + * Returns: + * + * If in protected mode, a constant identifying the segment register to use, + * among CS, SS, ES or DS. If in long mode, INAT_SEG_REG_IGNORE. + * + * -EINVAL in case of error. + */ +static int resolve_default_seg(struct insn *insn, struct pt_regs *regs, int off) +{ + if (user_64bit_mode(regs)) + return INAT_SEG_REG_IGNORE; + /* + * Resolve the default segment register as described in Section 3.7.4 + * of the Intel Software Development Manual Vol. 1: + * + * + DS for all references involving r[ABCD]X, and rSI. + * + If used in a string instruction, ES for rDI. Otherwise, DS. + * + AX, CX and DX are not valid register operands in 16-bit address + * encodings but are valid for 32-bit and 64-bit encodings. + * + -EDOM is reserved to identify for cases in which no register + * is used (i.e., displacement-only addressing). Use DS. + * + SS for rSP or rBP. + * + CS for rIP. + */ + + switch (off) { + case offsetof(struct pt_regs, ax): + case offsetof(struct pt_regs, cx): + case offsetof(struct pt_regs, dx): + /* Need insn to verify address size. */ + if (insn->addr_bytes == 2) + return -EINVAL; + + case -EDOM: + case offsetof(struct pt_regs, bx): + case offsetof(struct pt_regs, si): + return INAT_SEG_REG_DS; + + case offsetof(struct pt_regs, di): + if (is_string_insn(insn)) + return INAT_SEG_REG_ES; + return INAT_SEG_REG_DS; + + case offsetof(struct pt_regs, bp): + case offsetof(struct pt_regs, sp): + return INAT_SEG_REG_SS; + + case offsetof(struct pt_regs, ip): + return INAT_SEG_REG_CS; + + default: + return -EINVAL; + } +} + +/** + * resolve_seg_reg() - obtain segment register index + * @insn: Instruction with operands + * @regs: Register values as seen when entering kernel mode + * @regoff: Operand offset, in pt_regs, used to deterimine segment register + * + * Determine the segment register associated with the operands and, if + * applicable, prefixes and the instruction pointed by @insn. + * + * The segment register associated to an operand used in register-indirect + * addressing depends on: + * + * a) Whether running in long mode (in such a case segments are ignored, except + * if FS or GS are used). + * + * b) Whether segment override prefixes can be used. Certain instructions and + * registers do not allow override prefixes. + * + * c) Whether segment overrides prefixes are found in the instruction prefixes. + * + * d) If there are not segment override prefixes or they cannot be used, the + * default segment register associated with the operand register is used. + * + * The function checks first if segment override prefixes can be used with the + * operand indicated by @regoff. If allowed, obtain such overridden segment + * register index. Lastly, if not prefixes were found or cannot be used, resolve + * the segment register index to use based on the defaults described in the + * Intel documentation. In long mode, all segment register indexes will be + * ignored, except if overrides were found for FS or GS. All these operations + * are done using helper functions. + * + * The operand register, @regoff, is represented as the offset from the base of + * pt_regs. + * + * As stated, the main use of this function is to determine the segment register + * index based on the instruction, its operands and prefixes. Hence, @insn + * must be valid. However, if @regoff indicates rIP, we don't need to inspect + * @insn at all as in this case CS is used in all cases. This case is checked + * before proceeding further. + * + * Please note that this function does not return the value in the segment + * register (i.e., the segment selector) but our defined index. The segment + * selector needs to be obtained using get_segment_selector() and passing the + * segment register index resolved by this function. + * + * Returns: + * + * An index identifying the segment register to use, among CS, SS, DS, + * ES, FS, or GS. INAT_SEG_REG_IGNORE is returned if running in long mode. + * + * -EINVAL in case of error. + */ +static int resolve_seg_reg(struct insn *insn, struct pt_regs *regs, int regoff) +{ + int idx; + + /* + * In the unlikely event of having to resolve the segment register + * index for rIP, do it first. Segment override prefixes should not + * be used. Hence, it is not necessary to inspect the instruction, + * which may be invalid at this point. + */ + if (regoff == offsetof(struct pt_regs, ip)) { + if (user_64bit_mode(regs)) + return INAT_SEG_REG_IGNORE; + else + return INAT_SEG_REG_CS; + } + + if (!insn) + return -EINVAL; + + if (!check_seg_overrides(insn, regoff)) + return resolve_default_seg(insn, regs, regoff); + + idx = get_seg_reg_override_idx(insn); + if (idx < 0) + return idx; + + if (idx == INAT_SEG_REG_DEFAULT) + return resolve_default_seg(insn, regs, regoff); + + /* + * In long mode, segment override prefixes are ignored, except for + * overrides for FS and GS. + */ + if (user_64bit_mode(regs)) { + if (idx != INAT_SEG_REG_FS && + idx != INAT_SEG_REG_GS) + idx = INAT_SEG_REG_IGNORE; + } + + return idx; +} + +/** + * get_segment_selector() - obtain segment selector + * @regs: Register values as seen when entering kernel mode + * @seg_reg_idx: Segment register index to use + * + * Obtain the segment selector from any of the CS, SS, DS, ES, FS, GS segment + * registers. In CONFIG_X86_32, the segment is obtained from either pt_regs or + * kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained + * from pt_regs. DS, ES, FS and GS are obtained by reading the actual CPU + * registers. This done for only for completeness as in CONFIG_X86_64 segment + * registers are ignored. + * + * Returns: + * + * Value of the segment selector, including null when running in + * long mode. + * + * -EINVAL on error. + */ +static short get_segment_selector(struct pt_regs *regs, int seg_reg_idx) +{ +#ifdef CONFIG_X86_64 + unsigned short sel; + + switch (seg_reg_idx) { + case INAT_SEG_REG_IGNORE: + return 0; + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + savesegment(ds, sel); + return sel; + case INAT_SEG_REG_ES: + savesegment(es, sel); + return sel; + case INAT_SEG_REG_FS: + savesegment(fs, sel); + return sel; + case INAT_SEG_REG_GS: + savesegment(gs, sel); + return sel; + default: + return -EINVAL; + } +#else /* CONFIG_X86_32 */ + struct kernel_vm86_regs *vm86regs = (struct kernel_vm86_regs *)regs; + + if (v8086_mode(regs)) { + switch (seg_reg_idx) { + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + return vm86regs->ds; + case INAT_SEG_REG_ES: + return vm86regs->es; + case INAT_SEG_REG_FS: + return vm86regs->fs; + case INAT_SEG_REG_GS: + return vm86regs->gs; + case INAT_SEG_REG_IGNORE: + /* fall through */ + default: + return -EINVAL; + } + } + + switch (seg_reg_idx) { + case INAT_SEG_REG_CS: + return (unsigned short)(regs->cs & 0xffff); + case INAT_SEG_REG_SS: + return (unsigned short)(regs->ss & 0xffff); + case INAT_SEG_REG_DS: + return (unsigned short)(regs->ds & 0xffff); + case INAT_SEG_REG_ES: + return (unsigned short)(regs->es & 0xffff); + case INAT_SEG_REG_FS: + return (unsigned short)(regs->fs & 0xffff); + case INAT_SEG_REG_GS: + /* + * GS may or may not be in regs as per CONFIG_X86_32_LAZY_GS. + * The macro below takes care of both cases. + */ + return get_user_gs(regs); + case INAT_SEG_REG_IGNORE: + /* fall through */ + default: + return -EINVAL; + } +#endif /* CONFIG_X86_64 */ +} + static int get_reg_offset(struct insn *insn, struct pt_regs *regs, enum reg_type type) {