120 lines
5.2 KiB
Diff
120 lines
5.2 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Ingo Molnar <mingo@kernel.org>
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Date: Sat, 23 Dec 2017 13:14:25 +0100
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Subject: [PATCH] x86/insn-eval: Add utility functions to get segment selector
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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CVE-2017-5754
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When computing a linear address and segmentation is used, we need to know
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the base address of the segment involved in the computation. In most of
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the cases, the segment base address will be zero as in USER_DS/USER32_DS.
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However, it may be possible that a user space program defines its own
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segments via a local descriptor table. In such a case, the segment base
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address may not be zero. Thus, the segment base address is needed to
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calculate correctly the linear address.
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If running in protected mode, the segment selector to be used when
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computing a linear address is determined by either any of segment override
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prefixes in the instruction or inferred from the registers involved in the
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computation of the effective address; in that order. Also, there are cases
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when the segment override prefixes shall be ignored (i.e., code segments
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are always selected by the CS segment register; string instructions always
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use the ES segment register when using rDI register as operand). In long
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mode, segment registers are ignored, except for FS and GS. In these two
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cases, base addresses are obtained from the respective MSRs.
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For clarity, this process can be split into four steps (and an equal
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number of functions): determine if segment prefixes overrides can be used;
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parse the segment override prefixes, and use them if found; if not found
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or cannot be used, use the default segment registers associated with the
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operand registers. Once the segment register to use has been identified,
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read its value to obtain the segment selector.
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The method to obtain the segment selector depends on several factors. In
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32-bit builds, segment selectors are saved into a pt_regs structure
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when switching to kernel mode. The same is also true for virtual-8086
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mode. In 64-bit builds, segmentation is mostly ignored, except when
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running a program in 32-bit legacy mode. In this case, CS and SS can be
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obtained from pt_regs. DS, ES, FS and GS can be read directly from
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the respective segment registers.
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In order to identify the segment registers, a new set of #defines is
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introduced. It also includes two special identifiers. One of them
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indicates when the default segment register associated with instruction
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operands shall be used. Another one indicates that the contents of the
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segment register shall be ignored; this identifier is used when in long
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mode.
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Improvements-by: Borislav Petkov <bp@suse.de>
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Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Reviewed-by: Borislav Petkov <bp@suse.de>
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Cc: "Michael S. Tsirkin" <mst@redhat.com>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Dave Hansen <dave.hansen@linux.intel.com>
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Cc: ricardo.neri@intel.com
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Cc: Adrian Hunter <adrian.hunter@intel.com>
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Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
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Cc: Huang Rui <ray.huang@amd.com>
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Cc: Qiaowei Ren <qiaowei.ren@intel.com>
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Cc: Shuah Khan <shuah@kernel.org>
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Cc: Kees Cook <keescook@chromium.org>
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Cc: Jonathan Corbet <corbet@lwn.net>
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Cc: Jiri Slaby <jslaby@suse.cz>
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Cc: Dmitry Vyukov <dvyukov@google.com>
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Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
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Cc: Chris Metcalf <cmetcalf@mellanox.com>
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Cc: Brian Gerst <brgerst@gmail.com>
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Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
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Cc: Andy Lutomirski <luto@kernel.org>
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Cc: Colin Ian King <colin.king@canonical.com>
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Cc: Chen Yucong <slaoub@gmail.com>
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Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
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Cc: Vlastimil Babka <vbabka@suse.cz>
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Cc: Lorenzo Stoakes <lstoakes@gmail.com>
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Cc: Masami Hiramatsu <mhiramat@kernel.org>
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Cc: Paolo Bonzini <pbonzini@redhat.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>
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Cc: Thomas Garnier <thgarnie@google.com>
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Link: https://lkml.kernel.org/r/1509135945-13762-14-git-send-email-ricardo.neri-calderon@linux.intel.com
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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(Partially cherry picked from commit 32d0b95300db03c2b23b2ea2c94769a4a138e79d)
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(cherry picked from commit ca2c18cb10c8beb56dfe21321abdddc724cec4de)
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Signed-off-by: Andy Whitcroft <apw@canonical.com>
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Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
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(cherry picked from commit abd7780592a3687eacc0a295d4d2959bb11ff75f)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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arch/x86/include/asm/inat.h | 10 ++++++++++
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1 file changed, 10 insertions(+)
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diff --git a/arch/x86/include/asm/inat.h b/arch/x86/include/asm/inat.h
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index 02aff0867211..1c78580e58be 100644
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--- a/arch/x86/include/asm/inat.h
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+++ b/arch/x86/include/asm/inat.h
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@@ -97,6 +97,16 @@
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#define INAT_MAKE_GROUP(grp) ((grp << INAT_GRP_OFFS) | INAT_MODRM)
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#define INAT_MAKE_IMM(imm) (imm << INAT_IMM_OFFS)
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+/* Identifiers for segment registers */
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+#define INAT_SEG_REG_IGNORE 0
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+#define INAT_SEG_REG_DEFAULT 1
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+#define INAT_SEG_REG_CS 2
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+#define INAT_SEG_REG_SS 3
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+#define INAT_SEG_REG_DS 4
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+#define INAT_SEG_REG_ES 5
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+#define INAT_SEG_REG_FS 6
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+#define INAT_SEG_REG_GS 7
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+
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/* Attribute search APIs */
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extern insn_attr_t inat_get_opcode_attribute(insn_byte_t opcode);
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extern int inat_get_last_prefix_id(insn_byte_t last_pfx);
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--
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2.14.2
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