11787 Kernel needs to be built with retpolines
11788 Kernel needs to generally use RSB stuffing
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: John Levon <john.levon@joyent.com>

@@ -22,15 +22,17 @@
 /*
  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  * Use is subject to license terms.
  */
 
+/*
+ * Copyright 2019 Joyent, Inc.
+ */
+
 #ifndef _IA32_SYS_ASM_LINKAGE_H
 #define _IA32_SYS_ASM_LINKAGE_H
 
-#pragma ident   "%Z%%M% %I%     %E% SMI"
-
 #include <sys/stack.h>
 #include <sys/trap.h>
 
 #ifdef  __cplusplus
 extern "C" {

@@ -298,10 +300,50 @@
 
 #define NWORD   long
 
 #endif  /* __i386 */
 
+/*
+ * These macros should be used when making indirect calls in the kernel. They
+ * will perform a jump or call to the corresponding register in a way that knows
+ * about retpolines and handles whether such mitigations are enabled or not.
+ *
+ * INDIRECT_JMP_REG will jump to named register. INDIRECT_CALL_REG will instead
+ * do a call. These macros cannot be used to dereference a register. For
+ * example, if you need to do something that looks like the following:
+ *
+ *      call    *24(%rdi)
+ *      jmp     *(%r15)
+ *
+ * You must instead first do a movq into the corresponding location. You need to
+ * be careful to make sure that the register that its loaded into is safe to
+ * use. Often that register may be saved or used elsewhere so it may not be safe
+ * to clobber the value. Usually, loading into %rax would be safe. These would
+ * turn into something like:
+ *
+ *      movq 24(%rdi), %rdi; INDIRECT_CALL_REG(rdi)
+ *      movq (%r15), %r15; INDIRECT_JMP_REG(r15)
+ *
+ * If you are trying to call a global function, then use the following pattern
+ * (substituting the register in question):
+ *
+ *      leaq    my_favorite_function(%rip), %rax
+ *      INDIRECT_CALL_REG(rax)
+ *
+ * If you instead have a function pointer (say gethrtimef for example), then you
+ * need to do:
+ *
+ *      movq    my_favorite_function_pointer(%rip), %rax
+ *      INDIRECT_CALL_REG(rax)
+ */
+
+/* CSTYLED */
+#define INDIRECT_JMP_REG(reg)   jmp     __x86_indirect_thunk_/**/reg;
+
+/* CSTYLED */
+#define INDIRECT_CALL_REG(reg)  call    __x86_indirect_thunk_/**/reg;
+
 #endif /* _ASM */
 
 #ifdef  __cplusplus
 }
 #endif