This is a note to let you know that I've just added the patch titled
x86/alternative: Make custom return thunk unconditional
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-alternative-make-custom-return-thunk-unconditional.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 095b8303f3835c68ac4a8b6d754ca1c3b6230711 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon, 14 Aug 2023 13:44:30 +0200
Subject: x86/alternative: Make custom return thunk unconditional
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
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) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230814121148.775293785@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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(-)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -337,17 +337,18 @@ extern retpoline_thunk_t __x86_indirect_
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);
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -571,10 +571,6 @@ 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
@@ -63,6 +63,8 @@ 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)
{
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-6.4/x86-cpu-fix-up-srso_safe_ret-and-__x86_return_thunk.patch
queue-6.4/x86-static_call-fix-__static_call_fixup.patch
queue-6.4/x86-cpu-cleanup-the-untrain-mess.patch
queue-6.4/iopoll-call-cpu_relax-in-busy-loops.patch
queue-6.4/objtool-x86-fixup-frame-pointer-vs-rethunk.patch
queue-6.4/x86-retpoline-kprobes-skip-optprobe-check-for-indirect-jumps-with-retpolines-and-ibt.patch
queue-6.4/x86-retpoline-kprobes-fix-position-of-thunk-sections-with-config_lto_clang.patch
queue-6.4/x86-cpu-kvm-provide-untrain_ret_vm.patch
queue-6.4/x86-cpu-rename-srso_-.-_alias-to-srso_alias_-1.patch
queue-6.4/x86-alternative-make-custom-return-thunk-unconditional.patch
queue-6.4/x86-cpu-rename-original-retbleed-methods.patch
queue-6.4/objtool-x86-fix-srso-mess.patch
queue-6.4/x86-cpu-clean-up-srso-return-thunk-mess.patch
queue-6.4/x86-cpu-fix-__x86_return_thunk-symbol-type.patch
