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Message-ID: <20230809072200.782716727@infradead.org>
Date: Wed, 09 Aug 2023 09:12:23 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
David.Kaplan@....com, Andrew.Cooper3@...rix.com,
jpoimboe@...nel.org, gregkh@...uxfoundation.org
Subject: [RFC][PATCH 05/17] x86/cpu: Cleanup the untrain mess
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.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/nospec-branch.h | 19 +++++--------------
arch/x86/lib/retpoline.S | 7 +++++++
2 files changed, 12 insertions(+), 14 deletions(-)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -272,9 +272,9 @@
.endm
#ifdef CONFIG_CPU_UNRET_ENTRY
-#define CALL_ZEN_UNTRAIN_RET "call zen_untrain_ret"
+#define CALL_UNTRAIN_RET "call entry_untrain_ret"
#else
-#define CALL_ZEN_UNTRAIN_RET ""
+#define CALL_UNTRAIN_RET ""
#endif
/*
@@ -293,15 +293,10 @@
defined(CONFIG_CALL_DEPTH_TRACKING) || defined(CONFIG_CPU_SRSO)
VALIDATE_UNRET_END
ALTERNATIVE_3 "", \
- CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET, \
+ CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \
"call entry_ibpb", X86_FEATURE_ENTRY_IBPB, \
__stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
#endif
-
-#ifdef CONFIG_CPU_SRSO
- ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \
- "call srso_untrain_ret_alias", X86_FEATURE_SRSO_ALIAS
-#endif
.endm
.macro UNTRAIN_RET_FROM_CALL
@@ -309,15 +304,10 @@
defined(CONFIG_CALL_DEPTH_TRACKING)
VALIDATE_UNRET_END
ALTERNATIVE_3 "", \
- CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET, \
+ CALL_UNTRAIN_RET, X86_FEATURE_UNRET, \
"call entry_ibpb", X86_FEATURE_ENTRY_IBPB, \
__stringify(RESET_CALL_DEPTH_FROM_CALL), X86_FEATURE_CALL_DEPTH
#endif
-
-#ifdef CONFIG_CPU_SRSO
- ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \
- "call srso_untrain_ret_alias", X86_FEATURE_SRSO_ALIAS
-#endif
.endm
@@ -349,6 +339,7 @@ extern void zen_untrain_ret(void);
extern void srso_untrain_ret(void);
extern void srso_untrain_ret_alias(void);
+extern void entry_untrain_ret(void);
extern void entry_ibpb(void);
extern void (*x86_return_thunk)(void);
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -268,6 +268,13 @@ SYM_CODE_END(srso_safe_ret)
SYM_FUNC_END(srso_untrain_ret)
__EXPORT_THUNK(srso_untrain_ret)
+SYM_FUNC_START(entry_untrain_ret)
+ ALTERNATIVE_2 "jmp zen_untrain_ret", \
+ "jmp srso_untrain_ret", X86_FEATURE_SRSO, \
+ "jmp srso_untrain_ret_alias", X86_FEATURE_SRSO_ALIAS
+SYM_FUNC_END(entry_untrain_ret)
+__EXPORT_THUNK(entry_untrain_ret)
+
/*
* Both these do an unbalanced CALL to mess up the RSB, terminate with UD2
* to indicate noreturn.
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