linux-kernel - Re: [RFC PATCH 09/10] powerpc/fsl_booke/kaslr: support nokaslr cmdline parameter

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Message-ID: <e31851fd-5032-2787-ea36-c48a7a6ebbe9@c-s.fr>
Date:   Mon, 29 Jul 2019 13:38:57 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Jason Yan <yanaijie@...wei.com>, mpe@...erman.id.au,
        linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com,
        benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com,
        keescook@...omium.org, kernel-hardening@...ts.openwall.com
Cc:     linux-kernel@...r.kernel.org, wangkefeng.wang@...wei.com,
        yebin10@...wei.com, thunder.leizhen@...wei.com,
        jingxiangfeng@...wei.com, fanchengyang@...wei.com
Subject: Re: [RFC PATCH 09/10] powerpc/fsl_booke/kaslr: support nokaslr
 cmdline parameter



Le 17/07/2019 à 10:06, Jason Yan a écrit :
> One may want to disable kaslr when boot, so provide a cmdline parameter
> 'nokaslr' to support this.
> 
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> Cc: Diana Craciun <diana.craciun@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe Leroy <christophe.leroy@....fr>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>   arch/powerpc/kernel/kaslr_booke.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
> index 00339c05879f..e65a5d9d2ff1 100644
> --- a/arch/powerpc/kernel/kaslr_booke.c
> +++ b/arch/powerpc/kernel/kaslr_booke.c
> @@ -373,6 +373,18 @@ static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size
>   	return kaslr_offset;
>   }
>   
> +static inline __init bool kaslr_disabled(void)
> +{
> +	char *str;
> +
> +	str = strstr(early_command_line, "nokaslr");

Why using early_command_line instead of boot_command_line ?


> +	if ((str == early_command_line) ||
> +	    (str > early_command_line && *(str - 1) == ' '))

Is that stuff really needed ?

Why not just:

return strstr(early_command_line, "nokaslr") != NULL;

> +		return true;
> +
> +	return false;
> +}


> +
>   /*
>    * To see if we need to relocate the kernel to a random offset
>    * void *dt_ptr - address of the device tree
> @@ -388,6 +400,8 @@ notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
>   	kernel_sz = (unsigned long)_end - KERNELBASE;
>   
>   	kaslr_get_cmdline(dt_ptr);
> +	if (kaslr_disabled())
> +		return;
>   
>   	offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
>   
> 

Christophe