Re: [RFC] Second attempt at kernel secure boot support
From: Shea Levy
Date: Wed Oct 31 2012 - 13:08:28 EST
On 10/31/2012 01:08 PM, Alan Cox wrote:
On Wed, 31 Oct 2012 15:56:35 +0000
Matthew Garrett <mjg59@xxxxxxxxxxxxx> wrote:
1) Gain root.
2) Modify swap partition directly.
3) Force reboot.
4) Win.
Root should not have the ability to elevate themselves to running
arbitrary kernel code. Therefore, the above attack needs to be
impossible.
To protect swap you need to basically disallow any unencrypted swap (as
he OS can't prove any given swap device is local and inside the case) and
disallow the use of most disk management tools (so you'll need to write a
few new management interfaces or implement the BPF based command filters
that have been discussed for years).
Can any kernel memory get swapped? If not all root can do is mess with
the memory of other userspace processes, which isn't a use-case that
secure boot cares about from my understanding.
In addition of course there is no requirement that a device returns
the data you put on it so subverted removable media is a potential issue.
Or indeed just cheap memory sticks that do it anyway ;)
Oh and of course the file systems in default mode don't guarantee this so
you'll need to fix ext3, ext4 8)
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