linux-kernel - Re: [PATCH v41 01/13] Linux Random Number Generator

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Message-ID: <2681052.7KKukIsK80@positron.chronox.de>
Date:   Thu, 15 Jul 2021 07:24:52 +0200
From:   Stephan Müller <smueller@...onox.de>
To:     Tso Ted <tytso@....edu>, linux-crypto@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org, Willy Tarreau <w@....eu>,
        Nicolai Stange <nstange@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>
Subject: Re: [PATCH v41 01/13] Linux Random Number Generator

Am Donnerstag, 15. Juli 2021, 00:55:23 CEST schrieb kernel test robot:

Hi,

> All errors (new ones prefixed by >>):
> >> drivers/char/lrng/lrng_chacha20.c:32:8: error: structure variable
> >> 'chacha20' with 'latent_entropy' attribute has a non-integer field
> >> 'block'
>       32 | struct chacha20_state chacha20 __latent_entropy;
> 
>          |        ^~~~~~~~~~~~~~
> 
> vim +32 drivers/char/lrng/lrng_chacha20.c
> 
>     26
>     27	/*
>     28	 * Have a static memory blocks for the ChaCha20 DRNG instance to
> avoid calling 29	 * kmalloc too early in the boot cycle. For subsequent
> allocation requests, 30	 * such as per-NUMA-node DRNG instances, kmalloc
> will be used. 31	 */
> 
>   > 32	struct chacha20_state chacha20 __latent_entropy;
> 
>     33

Thanks for the notification.

I think this is a false-positive discussed before. __latent_entropy is 
seemingly allowed for an entire linear buffer as seen in the declaration of 
the variable input_pool_data in driver/char/random.c which is an array of u32.

The struct chacha20_state is a linear buffer of u32 words. 

struct chacha20_block {
        u32 constants[4];
        union {
                u32 u[CHACHA_KEY_SIZE_WORDS];
                u8  b[CHACHA_KEY_SIZE];
        } key;
        u32 counter;
        u32 nonce[3];
};

Therefore it should be identical to the aforementioned example. The 
__latent_entropy marker therefore seems to be appropriate for this structure.

Ciao
Stephan