Kdump with signed images

Vivek Goyal vgoyal at redhat.com
Thu Oct 25 14:55:20 EDT 2012

On Thu, Oct 25, 2012 at 02:40:21PM -0400, Mimi Zohar wrote:
> On Thu, 2012-10-25 at 10:10 -0400, Vivek Goyal wrote:
> > On Thu, Oct 25, 2012 at 02:10:01AM -0400, Mimi Zohar wrote:
> > 
> > [..]
> > > IMA-appraisal verifies the integrity of file data, while EVM verifies
> > > the integrity of the file metadata, such as LSM and IMA-appraisal
> > > labels.  Both 'security.ima' and 'security.evm' can contain digital
> > > signatures.
> > 
> > But the private key for creating these digital signature needs to be
> > on the target system?
> > 
> > Thanks
> > Vivek
> Absolutely not.  The public key needs to be added to the _ima or _evm
> keyrings.  Roberto Sassu modified dracut and later made equivalent
> changes to systemd.  Both have been upstreamed.

Putting public key in _ima or _evm keyring is not the problem. This is
just the verification part.

> Dmitry has a package
> that labels the filesystem called ima-evm-utils, which supports hash
> (IMA), hmac(EVM) and digital signatures(both).
> We're hoping that distro's would label all immutable files, not only elf
> executables, with digital signatures and mutable files with a hash.

So this labeling (digital signing) can happen at build time?

I suspect you need labeling to happen at system install time? If yes,
installer does not have the private key to sign anything.

IOW, if distro sign a file, they will most likely put signatures in
ELF header (something along the lines of signing PE/COFF binaries). But
I think you need digital signatures to be put in security.ima which are
stored in xattrs and xattrs are not generated till you put file in
question on target file system.


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