linux-kernel - init: How did init/do_mounts_rd.c overcome memory protection ?

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Message-ID: <CAPTae5LkwjLLwf2h0ovQt7twD1WxtGrcM0350hC8Hsvwo7ax9w@mail.gmail.com>
Date:	Tue, 10 Nov 2015 10:38:38 -0800
From:	Badhri Jagan Sridharan <badhri@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	dhowells@...hat.com, akpm@...ux-foundation.org
Subject: init: How did init/do_mounts_rd.c overcome memory protection ?

Mighty upstream,

I see that do_mounts_rd.c seems to make calls to sys_read and
sys_lseek functions. As these are syscall functions, they expects
some of the arguments to be from userspace.

I was going through the article that Greg KH wrote a while back:
http://www.linuxjournal.com/article/8110?page=0,1 . I don't see any
references to set_fs/get_fs under init/*. Does the memory protection
get enabled only in the later stage ? Or does do_mounts_rd.c accomplish
this in some other way ?

Thanks,
Badhri
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