linux-kernel - [PATCH v2 04/11] x86/alternative: Make custom return thunk unconditional

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Date:   Mon, 14 Aug 2023 13:44:30 +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,
        nik.borisov@...e.com
Subject: [PATCH v2 04/11] x86/alternative: Make custom return thunk unconditional

There is infrastructure to rewrite return thunks to point to any
random thunk one desires, unwrap that from CALL_THUNKS, which up to
now was the sole user of that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/nospec-branch.h |    4 ----
 arch/x86/kernel/alternative.c        |    2 --
 2 files changed, 6 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -347,11 +347,7 @@ extern void srso_untrain_ret(void);
 extern void srso_untrain_ret_alias(void);
 extern void entry_ibpb(void);
 
-#ifdef CONFIG_CALL_THUNKS
 extern void (*x86_return_thunk)(void);
-#else
-#define x86_return_thunk	(&__x86_return_thunk)
-#endif
 
 #ifdef CONFIG_CALL_DEPTH_TRACKING
 extern void __x86_return_skl(void);
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -687,9 +687,7 @@ void __init_or_module noinline apply_ret
 
 #ifdef CONFIG_RETHUNK
 
-#ifdef CONFIG_CALL_THUNKS
 void (*x86_return_thunk)(void) __ro_after_init = &__x86_return_thunk;
-#endif
 
 /*
  * Rewrite the compiler generated return thunk tail-calls.