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Date: Tue, 24 May 2016 10:16:09 -0700
From: Kees Cook <keescook@...omium.org>
To: Emese Revfy <re.emese@...il.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>, Michal Marek <mmarek@...e.com>,
LKML <linux-kernel@...r.kernel.org>,
Masahiro Yamada <yamada.masahiro@...ionext.com>, linux-kbuild <linux-kbuild@...r.kernel.org>,
"Theodore Ts'o" <tytso@....edu>, Andrew Morton <akpm@...ux-foundation.org>, Linux-MM <linux-mm@...ck.org>,
Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>, bart.vanassche@...disk.com,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v1 2/3] Mark functions with the latent_entropy attribute
On Mon, May 23, 2016 at 3:16 PM, Emese Revfy <re.emese@...il.com> wrote:
> These functions have been selected because they are init functions or
> are called at random times or they have variable loops.
>
> Based on work created by the PaX Team.
>
> Signed-off-by: Emese Revfy <re.emese@...il.com>
> [...]
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -188,6 +188,11 @@
> #endif /* GCC_VERSION >= 40300 */
>
> #if GCC_VERSION >= 40500
> +
> +#ifdef LATENT_ENTROPY_PLUGIN
> +#define __latent_entropy __attribute__((latent_entropy))
> +#endif
This deserves a full comment above it to describe its purpose and use
for when people go trying to figure out what it is and where to use
it. The commit message is a bit terse, so I'd try to expand both to
describe what function characteristics a developer should look for to
mark something with __latent_entropy.
> +
> /*
> * Mark a position in code as unreachable. This can be used to
> * suppress control flow warnings after asm blocks that transfer
> [...]
> diff --git a/include/linux/init.h b/include/linux/init.h
> index aedb254..68df2c3 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -37,9 +37,15 @@
> * section.
> */
>
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +#define add_meminit_latent_entropy
> +#else
> +#define add_meminit_latent_entropy __latent_entropy
> +#endif
> +
> /* These are for everybody (although not all archs will actually
> discard it in modules) */
> -#define __init __section(.init.text) __cold notrace
> +#define __init __section(.init.text) __cold notrace __latent_entropy
> #define __initdata __section(.init.data)
> #define __initconst __constsection(.init.rodata)
> #define __exitdata __section(.exit.data)
> @@ -92,7 +98,7 @@
> #define __exit __section(.exit.text) __exitused __cold notrace
>
> /* Used for MEMORY_HOTPLUG */
> -#define __meminit __section(.meminit.text) __cold notrace
> +#define __meminit __section(.meminit.text) __cold notrace add_meminit_latent_entropy
> #define __meminitdata __section(.meminit.data)
> #define __meminitconst __constsection(.meminit.rodata)
> #define __memexit __section(.memexit.text) __exitused __cold notrace
I was confused by these defines. :) Maybe "add_meminit_latent_entropy"
should be named "__memory_hotplug_only_latent_entropy" or something
like that?
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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