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x86/alternative: Make custom return thunk unconditional

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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
This commit is contained in:
Peter Zijlstra 2023-08-14 13:44:30 +02:00 committed by Borislav Petkov (AMD)
parent 4ae68b26c3
commit 095b8303f3
3 changed files with 7 additions and 8 deletions
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9
arch/x86/include/asm/nospec-branch.h
View File

@ -341,17 +341,18 @@ 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);

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

@ -687,10 +687,6 @@ 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

@ -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)
{