kprobes/x86: Disable optimizing on the function jumps to indirect thunk

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 <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Acked-by: David Woodhouse <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Ananth N Mavinakayanahalli <[e-mail]>
Cc: Arjan van de Ven <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: [e-mail]
Link: https://lkml.kernel.org/r/151629212062.10241.6991266100233002273.stgit@devbox

arch/x86/kernel/kprobes/opt.c

···
 #include <asm/debugreg.h>
 #include <asm/set_memory.h>
 #include <asm/sections.h>
+#include <asm/nospec-branch.h>
 
 #include "common.h"
 
···
 }
 
 /* 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 */
···
 	target = (unsigned long)insn->next_byte + insn->immediate.value;
 
 	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 */