linux-kernel - Re: [PATCH v4 1/2] powerpc/32: add stack protector support

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Message-ID: <20180926191615.GO23155@gate.crashing.org>
Date:   Wed, 26 Sep 2018 14:16:16 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] powerpc/32: add stack protector support

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