x86/retpoline: Swizzle retpoline thunk

Put the actual retpoline thunk as the original code so that it can
become more complicated. Specifically, it allows RET to be a JMP,
which can't be .altinstr_replacement since that doesn't do relocations
(except for the very first instruction).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index b2b2366..2cdd624 100644 (file)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -33,9 +33,9 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
        UNWIND_HINT_EMPTY
        ANNOTATE_NOENDBR
 
-       ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
-                     __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
-                     __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE
+       ALTERNATIVE_2 __stringify(RETPOLINE \reg), \
+                     __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE, \
+                     __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), ALT_NOT(X86_FEATURE_RETPOLINE)
 
 .endm