linux-kernel - Re: [RFC 2/2] initramfs with digital signature protection

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Message-ID: <CALLzPKZ7A6NW1ztX=hBjykMHkGofvtq6g-uK=Y2B2viskE9zDQ@mail.gmail.com>
Date:	Fri, 8 Feb 2013 18:24:48 +0200
From:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Jones <pjones@...hat.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/2] initramfs with digital signature protection

On Fri, Feb 8, 2013 at 5:49 PM, H. Peter Anvin <hpa@...or.com> wrote:
> Yes, but you can't umount rootfs.

But that was not a rootfs, but tmpfs/ramfs mounted to /root folder.

>
> "Kasatkin, Dmitry" <dmitry.kasatkin@...el.com> wrote:
>
>>On Wed, Feb 6, 2013 at 6:41 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>> The cleanup is not a umount, it is actually a tree walk unlinking the
>>contents.
>>>
>>
>>Please see that umounting ramfs releases the memory.
>>There was no forced cleanup.
>>"cp" copied about 2GB of content.
>>After umounting we got 2GB back to free RAM...
>>
>>kds@kds:~$ sudo mount -t ramfs testramfs /test
>>kds@kds:~$ sudo cp -r /usr/ /test
>>kds@kds:~$ du -sm /test
>>2154    /test
>>kds@kds:~$ free
>>                       total       used            free     shared
>>buffers     cached
>>Mem:       8058600    7855780     202820          0      24768
>>4819136
>>-/+ buffers/cache:    3011876    5046724
>>Swap:            0          0          0
>>kds@kds:~$ sudo umount /test
>>kds@kds:~$ free
>>                      total       used            free     shared
>>buffers     cached
>>Mem:       8058600    5644864    2413736          0      25268
>>2623956
>>-/+ buffers/cache:    2995640    5062960
>>Swap:            0          0          0
>>
>>The same happens also with tmpfs.
>>
>>- Dmitry
>>
>>> "Kasatkin, Dmitry" <dmitry.kasatkin@...el.com> wrote:
>>>
>>>>On Wed, Feb 6, 2013 at 7:04 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>>>> On 02/05/2013 02:09 PM, Kasatkin, Dmitry wrote:
>>>>>>
>>>>>>
>>>>>> It should not be like that. Actually when pre-init exits, cleanup
>>>>code
>>>>>> umount tmpfs, which in turn cleanups the RAM.
>>>>>>
>>>>>
>>>>> It doesn't quite... the rootfs is permanent.  This is also only one
>>>>usage
>>>>> mode: there are quite a few Linux systems running directly out of
>>>>initramfs.
>>>>>
>>>>
>>>>rootfs is not permanent when it is ramfs. It is cleaned up on switch
>>>>root.
>>>>It is easy to find out that it is empty by mounting : mount -t ramfs
>>>>rootfs /mnt/
>>>>
>>>>In the case of running from normal storage, of course, there is
>>>>ridicules remove the content.
>>>>
>>>>- Dmitry
>>>>
>>>>
>>>>>         -hpa
>>>>>
>>>>>
>>>>> --
>>>>> H. Peter Anvin, Intel Open Source Technology Center
>>>>> I work for Intel.  I don't speak on their behalf.
>>>>>
>>>
>>> --
>>> Sent from my mobile phone. Please excuse brevity and lack of
>>formatting.
>
> --
> Sent from my mobile phone. Please excuse brevity and lack of formatting.
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