Re: [PATCH v8 3/7] kexec, x86: clean boot_params area for entry-32bit path

From: "H. Peter Anvin" <hpa@zytor.com>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Simon Horman <horms@verge.net.au>,
	kexec@lists.infradead.org,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH v8 3/7] kexec, x86: clean boot_params area for entry-32bit path
Date: Wed, 30 Jan 2013 13:34:43 -0800	[thread overview]
Message-ID: <510991F3.9020006@zytor.com> (raw)
In-Reply-To: <1359581120-24397-4-git-send-email-yinghai@kernel.org>

On 01/30/2013 01:25 PM, Yinghai Lu wrote:
>  
> +static void clean_boot_params(unsigned char *real_mode, unsigned long size)
> +{
> +	unsigned long end;
> +
> +	/* clear value before header */
> +	memset(real_mode, 0, 0x1f1);
> +	/* clear value after setup_header  */
> +	end = *(real_mode + 0x201);

real_mode[0x201] might be clearer...

> +	end += 0x202;
> +	if (end < size)
> +		memset(real_mode + end, 0, size - end);
> +}

You don't actually need the test... the value is inherently smaller than
0x301 which is less than the size.

That being said, if you want to sanity-check it you can check that the
value is in a sensible range -- the permitted range is 0x22 to 0x7f
inclusive, corresponding to a total end value of 0x224 to 0x281.

	-hpa

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