From 53ebbe1c8c02aa7b7f072dd2f96bca4faa1daa59 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 14 Aug 2023 13:44:30 +0200 Subject: [PATCH] x86/alternative: Make custom return thunk unconditional commit 095b8303f3835c68ac4a8b6d754ca1c3b6230711 upstream. 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) Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230814121148.775293785@infradead.org Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/nospec-branch.h | 5 +++++ arch/x86/kernel/cpu/bugs.c | 2 ++ 2 files changed, 7 insertions(+) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 31fa631..9a4ffd3 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -210,7 +210,12 @@ 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 zen_untrain_ret(void); extern void srso_untrain_ret(void); extern void srso_untrain_ret_alias(void); diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index d98f33e..666f5be 100644 --- 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) { -- 2.7.4