Re: Should we automatically generate a module signing key at all?

[Andy Lutomirski]

On Fri, May 22, 2015 at 1:40 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, May 22, 2015 at 7:13 AM, George Spelvin <linux@xxxxxxxxxxx> wrote:
>>
>> 1) Create a tool to canonicalize the kernel and modules,
>>    stripping out the signatures before comparing them.  This has
>>    precedent in the way the prelink tool can un-prelink binaries
>>    so that hashes can be verified.
>
> So I'd obviously prefer this, so that we have just one model for verification.
>

In the threat model where module signatures matter in the first place
[1], this prevents reproducible builds from serving their purpose.  I
can build a kernel with a fresh signing key and throw away the private
key.  You can build a canonically identical kernel with a private key
that you keep.  A third party using mine is safe, but a third party
using yours is unsafe, even though the whole packages canonicalize to
exactly the same bytes.

[1] I still think this is a silly threat model, but many people
disagree with me.

--Andy
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