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x86/alternative: Make custom return thunk unconditional

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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>
This commit is contained in:
Peter Zijlstra 2023-08-14 13:44:30 +02:00 committed by Greg Kroah-Hartman
parent dd1a169b44
commit 1dfe6393d1
3 changed files with 6 additions and 8 deletions
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8
arch/x86/include/asm/nospec-branch.h
View File

@ -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

4
arch/x86/kernel/alternative.c
View File

@ -677,10 +677,6 @@ 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.
*

2
arch/x86/kernel/cpu/bugs.c
View File

@ -61,6 +61,8 @@ 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)
{