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Subject: Re: [RFC PATCH 09/10] powerpc/fsl_booke/kaslr: support nokaslr
 cmdline parameter
To:     Christophe Leroy <christophe.leroy@c-s.fr>, <mpe@ellerman.id.au>,
        <linuxppc-dev@lists.ozlabs.org>, <diana.craciun@nxp.com>,
        <benh@kernel.crashing.org>, <paulus@samba.org>,
        <npiggin@gmail.com>, <keescook@chromium.org>,
        <kernel-hardening@lists.openwall.com>
CC:     <linux-kernel@vger.kernel.org>, <wangkefeng.wang@huawei.com>,
        <yebin10@huawei.com>, <thunder.leizhen@huawei.com>,
        <jingxiangfeng@huawei.com>, <fanchengyang@huawei.com>
References: <20190717080621.40424-1-yanaijie@huawei.com>
 <20190717080621.40424-10-yanaijie@huawei.com>
 <e31851fd-5032-2787-ea36-c48a7a6ebbe9@c-s.fr>
From:   Jason Yan <yanaijie@huawei.com>
Message-ID: <846fa5fc-5d21-d974-e021-c314b554fa51@huawei.com>
Date:   Mon, 29 Jul 2019 22:04:31 +0800
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On 2019/7/29 19:38, Christophe Leroy wrote:
> 
> 
> 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@huawei.com>
>> Cc: Diana Craciun <diana.craciun@nxp.com>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
>> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: Nicholas Piggin <npiggin@gmail.com>
>> Cc: Kees Cook <keescook@chromium.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 ?
> 

Will switch to 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;
> 

This code is derived from other arch such as arm64/mips. It's trying to
make sure that 'nokaslr' is a separate word but not part of other words 
such as 'abcnokaslr'.

>> +        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
> 
> .
>