linux-kernel - Re: [PATCH v6 07/12] x86/cpu/keylocker: Load an internal wrapping key at boot-time

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Date:   Mon, 8 May 2023 14:56:27 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Eric Biggers <ebiggers@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        dm-devel@...hat.com, gmazyland@...il.com, luto@...nel.org,
        dave.hansen@...ux.intel.com, tglx@...utronix.de, bp@...e.de,
        mingo@...nel.org, x86@...nel.org, herbert@...dor.apana.org.au,
        ardb@...nel.org, dan.j.williams@...el.com, bernie.keany@...el.com,
        charishma1.gairuboyina@...el.com,
        lalithambika.krishnakumar@...el.com,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v6 07/12] x86/cpu/keylocker: Load an internal wrapping key
 at boot-time

On 5/8/23 11:18, Chang S. Bae wrote:
> On 5/5/2023 4:05 PM, Eric Biggers wrote:
>> On Mon, Apr 10, 2023 at 03:59:31PM -0700, Chang S. Bae wrote:
>>>   +#ifdef CONFIG_X86_KEYLOCKER
>>> +void setup_keylocker(struct cpuinfo_x86 *c);
>>> +void destroy_keylocker_data(void);
>>> +#else
>>> +#define setup_keylocker(c) do { } while (0)
>>> +#define destroy_keylocker_data() do { } while (0)
>>> +#endif
>>
>> Shouldn't the !CONFIG_X86_KEYLOCKER stubs be static inline functions
>> instead of
>> macros, so that type checking works?
> 
> I think either way works here. This macro is just for nothing.

Chang, I do prefer the 'static inline' as a general rule.  Think of this:

static inline void setup_keylocker(struct cpuinfo_x86 *c) {}

versus:

#define setup_keylocker(c) do { } while (0)

Imagine some dope does:

	char c;
	...
	setup_keylocker(c);

With the macro, they'll get no type warning.  The inline actually makes
it easier to find bugs because folks will get _some_ type checking no
matter how they compile the code.