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x86/retpolines: Enable the default thunk warning only on relevant configs

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The using-default-thunk warning check makes sense only with
configurations which actually enable the special return thunks.

Otherwise, it fires on unrelated 32-bit configs on which the special
return thunks won't even work (they're 64-bit only) and, what is more,
those configs even go off into the weeds when booting in the
alternatives patching code, leading to a dead machine.

Fixes: 4461438a84 ("x86/retpoline: Ensure default return thunk isn't used at runtime")
Reported-by: Klara Modin <klarasmodin@gmail.com>
Reported-by: Erhard Furtner <erhard_f@mailbox.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Klara Modin <klarasmodin@gmail.com>
Link: https://lore.kernel.org/r/78e0d19c-b77a-4169-a80f-2eef91f4a1d6@gmail.com
Link: https://lore.kernel.org/r/20240413024956.488d474e@yea
This commit is contained in:
Borislav Petkov (AMD) 2024-04-15 18:15:43 +02:00
parent 69129794d9
commit 6376306add
1 changed files with 7 additions and 0 deletions
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7
arch/x86/lib/retpoline.S
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@ -382,8 +382,15 @@ SYM_FUNC_END(call_depth_return_thunk)
SYM_CODE_START(__x86_return_thunk) SYM_CODE_START(__x86_return_thunk)
UNWIND_HINT_FUNC UNWIND_HINT_FUNC
ANNOTATE_NOENDBR ANNOTATE_NOENDBR
#if defined(CONFIG_MITIGATION_UNRET_ENTRY) || \
defined(CONFIG_MITIGATION_SRSO) || \
defined(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)
ALTERNATIVE __stringify(ANNOTATE_UNRET_SAFE; ret), \ ALTERNATIVE __stringify(ANNOTATE_UNRET_SAFE; ret), \
"jmp warn_thunk_thunk", X86_FEATURE_ALWAYS "jmp warn_thunk_thunk", X86_FEATURE_ALWAYS
#else
ANNOTATE_UNRET_SAFE
ret
#endif
int3 int3
SYM_CODE_END(__x86_return_thunk) SYM_CODE_END(__x86_return_thunk)
EXPORT_SYMBOL(__x86_return_thunk) EXPORT_SYMBOL(__x86_return_thunk)