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x86/alternative: Make custom return thunk unconditional

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commit 095b8303f3 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@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121148.775293785@infradead.org
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 Justin Hammond
parent 9a5b06e24d
commit 71ae8bd18d
2 changed files with 7 additions and 0 deletions
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5
arch/x86/include/asm/nospec-branch.h
View file

@ -195,7 +195,12 @@
_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 zen_untrain_ret(void);
extern void srso_untrain_ret(void);
extern void srso_untrain_ret_alias(void);

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

@ -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)
{