From 17880e4d5777df4770081ecf0750471cda57f86b Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Wed, 29 Mar 2017 13:59:15 +0900
Subject: [PATCH] kprobes/x86: Use instruction decoder for booster

Use x86 instruction decoder for checking whether the probed
instruction is able to boost or not, instead of hand-written
code.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ye Xiaolong <xiaolong.ye@intel.com>
Link: http://lkml.kernel.org/r/149076354563.22469.13379472209338986858.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/kprobes/core.c | 39 ++++++++++++++--------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 81d4dc786dae..6327f95832a0 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -169,35 +169,33 @@ NOKPROBE_SYMBOL(skip_prefixes);
  */
 int can_boost(kprobe_opcode_t *opcodes, void *addr)
 {
+	struct insn insn;
 	kprobe_opcode_t opcode;
-	kprobe_opcode_t *orig_opcodes = opcodes;
 
 	if (search_exception_tables((unsigned long)addr))
 		return 0;	/* Page fault may occur on this address. */
 
-retry:
-	if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
-		return 0;
-	opcode = *(opcodes++);
+	kernel_insn_init(&insn, (void *)opcodes, MAX_INSN_SIZE);
+	insn_get_opcode(&insn);
 
 	/* 2nd-byte opcode */
-	if (opcode == 0x0f) {
-		if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
-			return 0;
-		return test_bit(*opcodes,
+	if (insn.opcode.nbytes == 2)
+		return test_bit(insn.opcode.bytes[1],
 				(unsigned long *)twobyte_is_boostable);
-	}
+
+	if (insn.opcode.nbytes != 1)
+		return 0;
+
+	/* Can't boost Address-size override prefix */
+	if (unlikely(inat_is_address_size_prefix(insn.attr)))
+		return 0;
+
+	opcode = insn.opcode.bytes[0];
 
 	switch (opcode & 0xf0) {
-#ifdef CONFIG_X86_64
-	case 0x40:
-		goto retry; /* REX prefix is boostable */
-#endif
 	case 0x60:
-		if (0x63 < opcode && opcode < 0x67)
-			goto retry; /* prefixes */
-		/* can't boost Address-size override and bound */
-		return (opcode != 0x62 && opcode != 0x67);
+		/* can't boost "bound" */
+		return (opcode != 0x62);
 	case 0x70:
 		return 0; /* can't boost conditional jump */
 	case 0x90:
@@ -212,14 +210,9 @@ retry:
 		/* can boost in/out and absolute jmps */
 		return ((opcode & 0x04) || opcode == 0xea);
 	case 0xf0:
-		if ((opcode & 0x0c) == 0 && opcode != 0xf1)
-			goto retry; /* lock/rep(ne) prefix */
 		/* clear and set flags are boostable */
 		return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
 	default:
-		/* segment override prefixes are boostable */
-		if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
-			goto retry; /* prefixes */
 		/* CS override prefix and call are not boostable */
 		return (opcode != 0x2e && opcode != 0x9a);
 	}
-- 
2.25.1