linux-kernel - Re: [PATCH 1/1] x86/boot: clear some fields explicitly

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Date:   Wed, 24 Jul 2019 23:49:22 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     <hpa@...or.com>, <john.hubbard@...il.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] x86/boot: clear some fields explicitly

On 7/24/19 7:12 PM, hpa@...or.com wrote:
> On July 24, 2019 4:15:28 PM PDT, john.hubbard@...il.com wrote:
>> From: John Hubbard <jhubbard@...dia.com>
...
>> +		boot_params->ext_ramdisk_image = 0;
>> +		boot_params->ext_ramdisk_size = 0;
>> +		boot_params->ext_cmd_line_ptr = 0;
>> +
>> +		memset(&boot_params->_pad4, 0, sizeof(boot_params->_pad4));
>> 		memset(&boot_params->_pad7[0], 0,
>> 		       (char *)&boot_params->edd_mbr_sig_buffer[0] -
>> 			(char *)&boot_params->_pad7[0]);
> 
> The problem with this is that it will break silently when changes are made to this structure.
> 
> So, that is a NAK from me.
> 

Understood. It occurs to me, though, that it would be trivial to
just add build time assertions to check a few struct member offset
values, and fail out if they changed. That would give us everything:
warnings-free builds, and no silent failures.

Thoughts?

thanks,
-- 
John Hubbard
NVIDIA