linux-kernel - Re: [PATCH v35 01/13] Linux Random Number Generator

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Message-ID: <4146830.tdWV9SEqCh@tauon.chronox.de>
Date:   Sun, 20 Sep 2020 18:49:57 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Arnd Bergmann <arnd@...db.de>, kernel test robot <lkp@...el.com>
Cc:     kbuild-all@...ts.01.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>
Subject: Re: [PATCH v35 01/13] Linux Random Number Generator

Am Freitag, 18. September 2020, 15:02:17 CEST schrieb kernel test robot:

Hi,

> All errors (new ones prefixed by >>):
> >> drivers/char/lrng/lrng_chacha20.c:33:8: error: structure variable
> >> 'chacha20' with 'latent_entropy' attribute has a non-integer field
> >> 'block'
>       33 | struct chacha20_state chacha20 __latent_entropy;
> 
>          |        ^~~~~~~~~~~~~~
> 
> #
> https://github.com/0day-ci/linux/commit/ecb964754fd80cca434d6d2ad6db8f28a15
> 92fa1 git remote add linux-review https://github.com/0day-ci/linux
> git fetch --no-tags linux-review
> Stephan-M-ller/dev-random-a-new-approach/20200918-181505 git checkout
> ecb964754fd80cca434d6d2ad6db8f28a1592fa1
> vim +33 drivers/char/lrng/lrng_chacha20.c
> 
>     27
>     28	/*
>     29	 * Have a static memory blocks for the ChaCha20 DRNG instance to
> avoid calling 30	 * kmalloc too early in the boot cycle. For 
subsequent
> allocation requests, 31	 * such as per-NUMA-node DRNG instances, 
kmalloc
> will be used. 32	 */
> 
>   > 33	struct chacha20_state chacha20 __latent_entropy;

I do not think this report is valid. The following definitions apply:

struct chacha20_state {
        struct chacha20_block block;
};

struct chacha20_block {
        u32 constants[4];
        union {
#define CHACHA_KEY_SIZE_WORDS (CHACHA_KEY_SIZE / sizeof(u32))
                u32 u[CHACHA_KEY_SIZE_WORDS];
                u8  b[CHACHA_KEY_SIZE];
        } key;
        u32 counter;
        u32 nonce[3];
};


This implies that struct chacha20_state and thus the chacha20 variable is a 
linear buffer with in total 4 + 8 + 1 + 3  = 16 32-bit integers which are at 
least aligned on a 32-bit boundary and are designated as u32 integers.

Please let me know if I need to make a tweak to the definitions to convince 
the code analyzer it is a flat linear buffer consisting of integers and thus 
to understand the structure correctly.

Thanks a lot.

Ciao
Stephan