linux-kernel - Re: [patch 02/15] x86/cpu: Uninline CR4 accessors

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Date:   Mon, 20 Apr 2020 19:25:20 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Lendacky <Thomas.Lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [patch 02/15] x86/cpu: Uninline CR4 accessors

Christoph Hellwig <hch@...radead.org> writes:
>> --- a/arch/x86/kernel/cpu/common.c
>> +++ b/arch/x86/kernel/cpu/common.c
>> @@ -387,7 +387,30 @@ void native_write_cr4(unsigned long val)
>>  			  bits_missing);
>>  	}
>>  }
>> -EXPORT_SYMBOL(native_write_cr4);
>> +#if IS_MODULE(CONFIG_LKDTM)
>> +EXPORT_SYMBOL_GPL(native_write_cr4);
>> +#endif
>
> While this is better than what we had before we really need to have
> a discussion on lkdtm - it needs a lot of crap that otherwise wouldn't
> be exported, and I'm really worried about people enabling it and thus
> adding exports even if they are conditional.  Can we force the code
> to be built in require a boot option for it to be activated?

I can live with that :)