From 4fb8368bb6a0b7a50974722ddc16419b5a4c4559 Mon Sep 17 00:00:00 2001
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Fri, 19 Jan 2018 01:15:20 +0900
Subject: [PATCH] kprobes/x86: Disable optimizing on the function jumps to
 indirect thunk

commit c86a32c09f8ced67971a2310e3b0dda4d1749007 upstream.

Since indirect jump instructions will be replaced by jump
to __x86_indirect_thunk_*, those jmp instruction must be
treated as an indirect jump. Since optprobe prohibits to
optimize probes in the function which uses an indirect jump,
it also needs to find out the function which jump to
__x86_indirect_thunk_* and disable optimization.

Add a check that the jump target address is between the
__indirect_thunk_start/end when optimizing kprobe.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Link: https://lkml.kernel.org/r/151629212062.10241.6991266100233002273.stgit@devbox
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/kprobes/opt.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 4f98aad38237..3668f28cf5fc 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -40,6 +40,7 @@
 #include <asm/debugreg.h>
 #include <asm/set_memory.h>
 #include <asm/sections.h>
+#include <asm/nospec-branch.h>
 
 #include "common.h"
 
@@ -205,7 +206,7 @@ static int copy_optimized_instructions(u8 *dest, u8 *src)
 }
 
 /* Check whether insn is indirect jump */
-static int insn_is_indirect_jump(struct insn *insn)
+static int __insn_is_indirect_jump(struct insn *insn)
 {
 	return ((insn->opcode.bytes[0] == 0xff &&
 		(X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
@@ -239,6 +240,26 @@ static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
 	return (start <= target && target <= start + len);
 }
 
+static int insn_is_indirect_jump(struct insn *insn)
+{
+	int ret = __insn_is_indirect_jump(insn);
+
+#ifdef CONFIG_RETPOLINE
+	/*
+	 * Jump to x86_indirect_thunk_* is treated as an indirect jump.
+	 * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
+	 * older gcc may use indirect jump. So we add this check instead of
+	 * replace indirect-jump check.
+	 */
+	if (!ret)
+		ret = insn_jump_into_range(insn,
+				(unsigned long)__indirect_thunk_start,
+				(unsigned long)__indirect_thunk_end -
+				(unsigned long)__indirect_thunk_start);
+#endif
+	return ret;
+}
+
 /* Decode whole function to ensure any instructions don't jump into target */
 static int can_optimize(unsigned long paddr)
 {