5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra peterz@infradead.org
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 --- arch/x86/include/asm/nospec-branch.h | 8 ++++---- arch/x86/kernel/alternative.c | 4 ---- arch/x86/kernel/cpu/bugs.c | 2 ++ 3 files changed, 6 insertions(+), 8 deletions(-)
--- 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
--- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -522,10 +522,6 @@ 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. * --- 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) {