Commit 095b8303 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov (AMD)
Browse files

x86/alternative: Make custom return thunk unconditional 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121148.775293785@infradead.org
parent 4ae68b26

arch/x86/include/asm/nospec-branch.h

+5 −4
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/alternative.c

+0 −4
Original line number Diff line number Diff line
@@ -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.

 *

arch/x86/kernel/cpu/bugs.c

+2 −0
Original line number Diff line number Diff line
@@ -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)

{