x86/alternative: Make custom return thunk unconditional

Upstream commit: 095b8303f3835c68ac4a8b6d754ca1c3b6230711

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.

  [ bp: Make the thunks visible on 32-bit and add ifdeffery for the
    32-bit builds. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121148.775293785@infradead.org
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 319b4249ea01e0c5b4a3ff2b3cda9fc0b9d5707f..7711ba5342a1a88a06bae4803620929ee9de84cf 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -190,7 +190,11 @@
        _ASM_PTR " 999b\n\t"                                    \
        ".popsection\n\t"
 
+#ifdef CONFIG_RETHUNK
 extern void __x86_return_thunk(void);
+#else
+static inline void __x86_return_thunk(void) {}
+#endif
 
 extern void retbleed_return_thunk(void);
 extern void srso_return_thunk(void);
@@ -203,11 +207,7 @@ extern void srso_alias_untrain_ret(void);
 extern void entry_untrain_ret(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_RETPOLINE
 

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 4d3715f6aaab3ed366ce9c5cb1902607292162f9..9ceef8515c0312b292d67ac2d2ffbb1b7d6acd1d 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -677,10 +677,6 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
 
 #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.
  *

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fc20f24b422a9e02ce1f8cf5a66d36b29b20dd7f..d9fda0b6eb19e2920c0c06c956b1884fae3ccc5b 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -61,6 +61,8 @@ EXPORT_SYMBOL_GPL(x86_pred_cmd);
 
 static DEFINE_MUTEX(spec_ctrl_mutex);
 
+void (*x86_return_thunk)(void) __ro_after_init = &__x86_return_thunk;
+
 /* Update SPEC_CTRL MSR and its cached copy unconditionally */
 static void update_spec_ctrl(u64 val)
 {