linux-kernel - Re: [PATCH] latent_entropy: avoid build error when plugin cflags are not set

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Date:   Tue, 7 May 2019 09:16:29 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Vasily Gorbik <gor@...ux.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Emese Revfy <re.emese@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] latent_entropy: avoid build error when plugin cflags are
 not set

On Tue, May 7, 2019 at 7:28 AM Vasily Gorbik <gor@...ux.ibm.com> wrote:
> Some architectures set up CFLAGS for linux decompressor phase from
> scratch and do not include GCC_PLUGINS_CFLAGS. Since "latent_entropy"
> variable declaration is generated by the plugin code itself including
> linux/random.h in decompressor code then would cause a build
> error. E.g. on s390:
>
> In file included from ./include/linux/net.h:22,
>                  from ./include/linux/skbuff.h:29,
>                  from ./include/linux/if_ether.h:23,
>                  from ./arch/s390/include/asm/diag.h:12,
>                  from arch/s390/boot/startup.c:8:
> ./include/linux/random.h: In function 'add_latent_entropy':
> ./include/linux/random.h:26:39: error: 'latent_entropy' undeclared
> (first use in this function); did you mean 'add_latent_entropy'?
>    26 |  add_device_randomness((const void *)&latent_entropy,
>       |                                       ^~~~~~~~~~~~~~
>       |                                       add_latent_entropy
> ./include/linux/random.h:26:39: note: each undeclared identifier is
> reported only once for each function it appears in
>
> The build error is triggered by commit a80313ff91ab ("s390/kernel:
> introduce .dma sections") which made it into 5.2 merge window.
>
> To address that avoid using CONFIG_GCC_PLUGIN_LATENT_ENTROPY in
> favour of LATENT_ENTROPY_PLUGIN definition which is defined as a
> part of gcc plugins cflags and hence reflect more accurately when gcc
> plugin is active. Besides that it is also used for similar purpose in
> linux/compiler-gcc.h for latent_entropy attribute definition.
>
> Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>

Thanks for fixing this! Do you want to take it via the s390 tree?

Acked-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  include/linux/random.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/random.h b/include/linux/random.h
> index 445a0ea4ff49..d4eb9b3789ad 100644
> --- a/include/linux/random.h
> +++ b/include/linux/random.h
> @@ -20,7 +20,7 @@ struct random_ready_callback {
>
>  extern void add_device_randomness(const void *, unsigned int);
>
> -#if defined(CONFIG_GCC_PLUGIN_LATENT_ENTROPY) && !defined(__CHECKER__)
> +#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
>  static inline void add_latent_entropy(void)
>  {
>         add_device_randomness((const void *)&latent_entropy,
> --
> 2.18.0.13.gd42ae10
>


-- 
Kees Cook