linux-kernel - Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't used at runtime

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Date:   Wed, 18 Oct 2023 15:38:56 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        David Kaplan <david.kaplan@....com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org
Subject: Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't
 used at runtime


* Borislav Petkov <bp@...en8.de> wrote:

> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index bb0ab8466b91..e4b2dfbf3de5 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2849,3 +2849,8 @@ ssize_t cpu_show_gds(struct device *dev, struct device_attribute *attr, char *bu
>  	return cpu_show_common(dev, attr, buf, X86_BUG_GDS);
>  }
>  #endif
> +
> +void check_thunks(void)
> +{
> +	WARN(1, "Unconverted return thunk\n");

If then WARN_ONCE().

Thanks,

	Ingo