x86/retpoline: Fix retpoline unwind

Currently objtool cannot understand retpolines, and thus cannot
generate ORC unwind information for them. This means that we cannot
unwind from the middle of a retpoline.

The recent ANNOTATE_INTRA_FUNCTION_CALL and UNWIND_HINT_RET_OFFSET
support in objtool enables it to understand the basic retpoline
construct. A further problem is that the ORC unwind information is
alternative invariant; IOW. every alternative should have the same
ORC, retpolines obviously violate this. This means we need to
out-of-line them.

Since all GCC generated code already uses out-of-line retpolines, this
should not affect performance much, if anything.

This will enable objtool to generate valid ORC data for the
out-of-line copies, which means we can correctly and reliably unwind
through a retpoline.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200428191700.210835357@infradead.org

1 files changed, 8 insertions, 48 deletions

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index d3269b69728a..d52d1aacdd97 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -13,15 +13,6 @@
 #include <asm/unwind_hints.h>
 
 /*
- * This should be used immediately before a retpoline alternative. It tells
- * objtool where the retpolines are so that it can make sense of the control
- * flow by just reading the original instruction(s) and ignoring the
- * alternatives.
- */
-#define ANNOTATE_NOSPEC_ALTERNATIVE \
-	ANNOTATE_IGNORE_ALTERNATIVE
-
-/*
  * Fill the CPU return stack buffer.
  *
  * Each entry in the RSB, if used for a speculative 'ret', contains an
@@ -83,44 +74,15 @@
 .endm
 
 /*
- * These are the bare retpoline primitives for indirect jmp and call.
- * Do not use these directly; they only exist to make the ALTERNATIVE
- * invocation below less ugly.
- */
-.macro RETPOLINE_JMP reg:req
-	call	.Ldo_rop_\@
-.Lspec_trap_\@:
-	pause
-	lfence
-	jmp	.Lspec_trap_\@
-.Ldo_rop_\@:
-	mov	\reg, (%_ASM_SP)
-	ret
-.endm
-
-/*
- * This is a wrapper around RETPOLINE_JMP so the called function in reg
- * returns to the instruction after the macro.
- */
-.macro RETPOLINE_CALL reg:req
-	jmp	.Ldo_call_\@
-.Ldo_retpoline_jmp_\@:
-	RETPOLINE_JMP \reg
-.Ldo_call_\@:
-	call	.Ldo_retpoline_jmp_\@
-.endm
-
-/*
  * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
  * indirect jmp/call which may be susceptible to the Spectre variant 2
  * attack.
  */
 .macro JMP_NOSPEC reg:req
 #ifdef CONFIG_RETPOLINE
-	ANNOTATE_NOSPEC_ALTERNATIVE
-	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg),	\
-		__stringify(RETPOLINE_JMP %\reg), X86_FEATURE_RETPOLINE,\
-		__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
+	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
+		      __stringify(jmp __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \
+		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
 #else
 	jmp	*%\reg
 #endif
@@ -128,10 +90,9 @@
 
 .macro CALL_NOSPEC reg:req
 #ifdef CONFIG_RETPOLINE
-	ANNOTATE_NOSPEC_ALTERNATIVE
-	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg),\
-		__stringify(RETPOLINE_CALL %\reg), X86_FEATURE_RETPOLINE,\
-		__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD
+	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
+		      __stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE, \
+		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_AMD
 #else
 	call	*%\reg
 #endif
@@ -165,16 +126,16 @@
  * which is ensured when CONFIG_RETPOLINE is defined.
  */
 # define CALL_NOSPEC						\
-	ANNOTATE_NOSPEC_ALTERNATIVE				\
 	ALTERNATIVE_2(						\
 	ANNOTATE_RETPOLINE_SAFE					\
 	"call *%[thunk_target]\n",				\
-	"call __x86_indirect_thunk_%V[thunk_target]\n",		\
+	"call __x86_retpoline_%V[thunk_target]\n",		\
 	X86_FEATURE_RETPOLINE,					\
 	"lfence;\n"						\
 	ANNOTATE_RETPOLINE_SAFE					\
 	"call *%[thunk_target]\n",				\
 	X86_FEATURE_RETPOLINE_AMD)
+
 # define THUNK_TARGET(addr) [thunk_target] "r" (addr)
 
 #else /* CONFIG_X86_32 */
@@ -184,7 +145,6 @@
  * here, anyway.
  */
 # define CALL_NOSPEC						\
-	ANNOTATE_NOSPEC_ALTERNATIVE				\
 	ALTERNATIVE_2(						\
 	ANNOTATE_RETPOLINE_SAFE					\
 	"call *%[thunk_target]\n",				\