From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <segher@kernel.crashing.org>
Received: from gate.crashing.org (gate.crashing.org [63.228.1.57])
 (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by lists.ozlabs.org (Postfix) with ESMTPS id 42L73X49DlzF3Ld
 for <linuxppc-dev@lists.ozlabs.org>; Thu, 27 Sep 2018 05:16:56 +1000 (AEST)
Date: Wed, 26 Sep 2018 14:16:16 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
 Paul Mackerras <paulus@samba.org>,
 Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org,
 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/2] powerpc/32: add stack protector support
Message-ID: <20180926191615.GO23155@gate.crashing.org>
References: <d6c43ab708bf9ae1266c745fece457ed2da43d7c.1537961921.git.christophe.leroy@c-s.fr>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
In-Reply-To: <d6c43ab708bf9ae1266c745fece457ed2da43d7c.1537961921.git.christophe.leroy@c-s.fr>
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>

On Wed, Sep 26, 2018 at 11:40:38AM +0000, Christophe Leroy wrote:
> +static __always_inline void boot_init_stack_canary(void)
> +{
> +	unsigned long canary;
> +
> +	/* Try to get a semi random initial value. */
> +	get_random_bytes(&canary, sizeof(canary));
> +	canary ^= mftb();
> +	canary ^= LINUX_VERSION_CODE;
> +
> +	current->stack_canary = canary;
> +}

I still think you should wait until there is entropy available.  You
haven't answered my questions about that (or I didn't see them): what
does the kernel do in other similar cases?

Looks great otherwise!


Segher