Date:   Fri, 18 Aug 2017 17:27:56 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...e.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liang Z Li <liang.z.li@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, ricardo.neri@...el.com,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Colin Ian King <colin.king@...onical.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Qiaowei Ren <qiaowei.ren@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: [PATCH v8 15/28] x86/insn-eval: Add function to get default params of code segment

Obtain the default values of the address and operand sizes as specified in
the D and L bits of the the segment descriptor selected by the register
CS. The function can be used for both protected and long modes.
For virtual-8086 mode, the default address and operand sizes are always 2
bytes.

The returned parameters are encoded in a signed 8-bit data type. Auxiliar
macros are provided to encode and decode such values.

Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Adam Buchbinder <adam.buchbinder@...il.com>
Cc: Colin Ian King <colin.king@...onical.com>
Cc: Lorenzo Stoakes <lstoakes@...il.com>
Cc: Qiaowei Ren <qiaowei.ren@...el.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
Cc: x86@...nel.org
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
---
 arch/x86/include/asm/insn-eval.h |  5 ++++
 arch/x86/lib/insn-eval.c         | 59 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 7f3c7fe72cd0..e8c3e7cd1673 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -11,9 +11,14 @@
 #include <linux/err.h>
 #include <asm/ptrace.h>
 
+#define INSN_CODE_SEG_ADDR_SZ(params) ((params >> 4) & 0xf)
+#define INSN_CODE_SEG_OPND_SZ(params) (params & 0xf)
+#define INSN_CODE_SEG_PARAMS(oper_sz, addr_sz) (oper_sz | (addr_sz << 4))
+
 void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
 int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs);
 unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
 				int regoff);
+char insn_get_code_seg_defaults(struct pt_regs *regs);
 
 #endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 2c5e7081957d..a8e12bd0aecd 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -584,6 +584,65 @@ static unsigned long get_seg_limit(struct pt_regs *regs, struct insn *insn,
 }
 
 /**
+ * insn_get_code_seg_defaults() - Obtain code segment default parameters
+ * @regs:	Structure with register values as seen when entering kernel mode
+ *
+ * Obtain the default parameters of the code segment: address and operand sizes.
+ * The code segment is obtained from the selector contained in the CS register
+ * in regs. In protected mode, the default address is determined by inspecting
+ * the L and D bits of the segment descriptor. In virtual-8086 mode, the default
+ * is always two bytes for both address and operand sizes.
+ *
+ * Return: A signed 8-bit value containing the default parameters on success and
+ * -EINVAL on error.
+ */
+char insn_get_code_seg_defaults(struct pt_regs *regs)
+{
+	struct desc_struct *desc;
+	unsigned short sel;
+
+	if (v8086_mode(regs))
+		/* Address and operand size are both 16-bit. */
+		return INSN_CODE_SEG_PARAMS(2, 2);
+
+	sel = (unsigned short)regs->cs;
+
+	desc = get_desc(sel);
+	if (!desc)
+		return -EINVAL;
+
+	/*
+	 * The most significant byte of the Type field of the segment descriptor
+	 * determines whether a segment contains data or code. If this is a data
+	 * segment, return error.
+	 */
+	if (!(desc->type & BIT(3)))
+		return -EINVAL;
+
+	switch ((desc->l << 1) | desc->d) {
+	case 0: /*
+		 * Legacy mode. CS.L=0, CS.D=0. Address and operand size are
+		 * both 16-bit.
+		 */
+		return INSN_CODE_SEG_PARAMS(2, 2);
+	case 1: /*
+		 * Legacy mode. CS.L=0, CS.D=1. Address and operand size are
+		 * both 32-bit.
+		 */
+		return INSN_CODE_SEG_PARAMS(4, 4);
+	case 2: /*
+		 * IA-32e 64-bit mode. CS.L=1, CS.D=0. Address size is 64-bit;
+		 * operand size is 32-bit.
+		 */
+		return INSN_CODE_SEG_PARAMS(4, 8);
+	case 3: /* Invalid setting. CS.L=1, CS.D=1 */
+		/* fall through */
+	default:
+		return -EINVAL;
+	}
+}
+
+/**
  * insn_get_modrm_rm_off() - 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
-- 
2.13.0

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