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 6.1-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-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c203b857ba7dedefdf9924a56be434b46a73765a 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>
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@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230814121148.775293785@xxxxxxxxxxxxx
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -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
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -537,10 +537,6 @@ 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)
{
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-6.1/x86-alternative-make-custom-return-thunk-unconditional.patch
queue-6.1/x86-returnthunk-allow-different-return-thunks.patch
queue-6.1/sched-rt-sysctl_sched_rr_timeslice-show-default-timeslice-after-reset.patch
