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 44c78af98af4bb1e4c2acf10a844828c2c1d2b83..d3706de91a934bf82bf29842906db7943904542a 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -205,7 +205,11 @@
 typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE];
 extern retpoline_thunk_t __x86_indirect_thunk_array[];
 
+#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);
@@ -218,11 +222,7 @@ 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 5c11f688a10112f547806cb800fb4bff877fb2ab..69f85e2746119665a9e8169ad10229b627008c64 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -537,10 +537,6 @@ 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 208e4938f35ba657ebe7e9f5e6d90cbff855e90d..13dffc43ded020ce9e24c02ea8c8fed0eb2bcd3b 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -62,6 +62,8 @@ 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)
 {