linux-kernel - Re: [PATCHv2 1/2] init: Move stack canary initialization after setup

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Message-ID: <CAGXu5jK=K5DmW=TODb6ZOd7fHqhjHjoOP2yTW-v_0jONsti4yw@mail.gmail.com>
Date:   Wed, 16 Aug 2017 15:50:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Laura Abbott <lauraa@...eaurora.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Micay <danielmicay@...il.com>
Subject: Re: [PATCHv2 1/2] init: Move stack canary initialization after setup_arch

On Wed, Aug 16, 2017 at 3:46 PM, Laura Abbott <labbott@...hat.com> wrote:
> From: Laura Abbott <lauraa@...eaurora.org>
>
> Stack canary intialization involves getting a random number.
> Getting this random number may involve accessing caches or other
> architectural specific features which are not available until
> after the architecture is setup. Move the stack canary initialization
> later to accomodate this.
>
> Signed-off-by: Laura Abbott <lauraa@...eaurora.org>
> Signed-off-by: Laura Abbott <labbott@...hat.com>

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

-Kees

> ---
> v2: Also moved add_latent_entropy per suggestion of Kees.
> ---
>  init/main.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/init/main.c b/init/main.c
> index 052481fbe363..21d599eaad06 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -515,12 +515,6 @@ asmlinkage __visible void __init start_kernel(void)
>         smp_setup_processor_id();
>         debug_objects_early_init();
>
> -       /*
> -        * Set up the initial canary ASAP:
> -        */
> -       add_latent_entropy();
> -       boot_init_stack_canary();
> -
>         cgroup_init_early();
>
>         local_irq_disable();
> @@ -534,6 +528,11 @@ asmlinkage __visible void __init start_kernel(void)
>         page_address_init();
>         pr_notice("%s", linux_banner);
>         setup_arch(&command_line);
> +       /*
> +        * Set up the the initial canary and entropy after arch
> +        */
> +       add_latent_entropy();
> +       boot_init_stack_canary();
>         mm_init_cpumask(&init_mm);
>         setup_command_line(command_line);
>         setup_nr_cpu_ids();
> --
> 2.13.0
>



-- 
Kees Cook
Pixel Security