x86/cpu: Cleanup the untrain mess

commit e7c25c4 upstream. Since there can only be one active return_thunk, there only needs be one (matching) untrain_ret. It fundamentally doesn't make sense to allow multiple untrain_ret at the same time. Fold all the 3 different untrain methods into a single (temporary) helper stub. Fixes: fb3bd91 ("x86/srso: Add a Speculative RAS Overflow mitigation") Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Signed-off-by: Borislav Petkov (AMD) <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Greg Kroah-Hartman <[email protected]>
chargebyte · lategoodbye · Aug 29, 2023 · Aug 4, 2023 · Aug 2, 2023 · Aug 3, 2023
commit 529a9f087a7e03e87dd9c2acd687739e3e348045
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
@@ -168,9 +168,9 @@
 .endm
 
 #ifdef CONFIG_CPU_UNRET_ENTRY
-#define CALL_ZEN_UNTRAIN_RET	"call retbleed_untrain_ret"
+#define CALL_UNTRAIN_RET	"call entry_untrain_ret"
 #else
-#define CALL_ZEN_UNTRAIN_RET	""
+#define CALL_UNTRAIN_RET	""
 #endif
 
 /*
@@ -189,14 +189,9 @@
 	defined(CONFIG_CPU_SRSO)
 	ANNOTATE_UNRET_END
 	ALTERNATIVE_2 "",						\
-	              CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET,		\
+		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
 		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB
 #endif
-
-#ifdef CONFIG_CPU_SRSO
-	ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \
-			  "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS
-#endif
 .endm
 
 #else /* __ASSEMBLY__ */
@@ -224,6 +219,7 @@ extern void retbleed_untrain_ret(void);
 extern void srso_untrain_ret(void);
 extern void srso_alias_untrain_ret(void);
 
+extern void entry_untrain_ret(void);
 extern void entry_ibpb(void);
 
 #ifdef CONFIG_RETPOLINE

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
@@ -2429,6 +2429,7 @@ static void __init srso_select_mitigation(void)
 			 * like ftrace, static_call, etc.
 			 */
 			setup_force_cpu_cap(X86_FEATURE_RETHUNK);
+			setup_force_cpu_cap(X86_FEATURE_UNRET);
 
 			if (boot_cpu_data.x86 == 0x19) {
 				setup_force_cpu_cap(X86_FEATURE_SRSO_ALIAS);

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
@@ -233,6 +233,13 @@ SYM_CODE_START(srso_return_thunk)
 	ud2
 SYM_CODE_END(srso_return_thunk)
 
+SYM_FUNC_START(entry_untrain_ret)
+	ALTERNATIVE_2 "jmp retbleed_untrain_ret", \
+		      "jmp srso_untrain_ret", X86_FEATURE_SRSO, \
+		      "jmp srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS
+SYM_FUNC_END(entry_untrain_ret)
+__EXPORT_THUNK(entry_untrain_ret)
+
 SYM_CODE_START(__x86_return_thunk)
 	UNWIND_HINT_FUNC
 	ANNOTATE_NOENDBR