From 29fa1c8bcbb299f699e263bd9ee94b6ef2c31cdc 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 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 CVE-2023-20569 (cherry picked from commit 095b8303f3835c68ac4a8b6d754ca1c3b6230711) Signed-off-by: Thadeu Lima de Souza Cascardo Acked-by: Roxana Nicolescu Acked-by: Stefan Bader Signed-off-by: Stefan Bader --- arch/x86/include/asm/nospec-branch.h | 9 +++++---- arch/x86/kernel/alternative.c | 4 ---- arch/x86/kernel/cpu/bugs.c | 2 ++ 3 files changed, 7 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 7316c2d43c8d..015f8f1e4632 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -336,17 +336,18 @@ extern retpoline_thunk_t __x86_indirect_thunk_array[]; extern retpoline_thunk_t __x86_indirect_call_thunk_array[]; extern retpoline_thunk_t __x86_indirect_jump_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); 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); diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index bc8e654de660..6c5ad0966b46 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -573,10 +573,6 @@ 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 6284936d0e67..84c3cfb2175c 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) { -- 2.39.5