linux-kernel - Re: [PATCH 07/27] kexec_file: Disable at runtime if securelevel has been set

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Message-Id: <1509027463.5886.26.camel@linux.vnet.ibm.com>
Date:   Thu, 26 Oct 2017 10:17:43 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     joeyli <jlee@...e.com>
Cc:     David Howells <dhowells@...hat.com>,
        linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        linux-efi@...r.kernel.org, matthew.garrett@...ula.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        jforbes@...hat.com
Subject: Re: [PATCH 07/27] kexec_file: Disable at runtime if securelevel has
 been set

On Thu, 2017-10-26 at 15:42 +0800, joeyli wrote:
> Hi Mimi,
> 
> Thank you for reviewing.
> 
> On Mon, Oct 23, 2017 at 11:54:43AM -0400, Mimi Zohar wrote:
> > On Thu, 2017-10-19 at 15:51 +0100, David Howells wrote:
> > > From: Chun-Yi Lee <joeyli.kernel@...il.com>
> > > 
> > > When KEXEC_VERIFY_SIG is not enabled, kernel should not loads image
> > > through kexec_file systemcall if securelevel has been set.
> > 
> > The patch title and description needs to be updated to refer to
> > lockdown, not securelevel.
> > 
> > As previously mentioned the last time these patches were posted, this
> > leaves out testing to see if the integrity subsystem is enabled.
> > 
> > Commit 503ceaef8e2e "ima: define a set of appraisal rules requiring
> > file signatures" was upstreamed.  An additional patch could force
> > these rules to be added to the custom policy, if lockdown is enabled.
> >  This and other patches in this series could then check to see if
> > is_ima_appraise_enabled() is true.
> > 
> > Mimi
> >
> 
> I have updated the patch title and description, and I also added
> is_ima_appraise_enabled() as the following. Is it good to you?

Yes, that works.  Thanks!  Remember is_ima_appraise_enabled() is
dependent on the "ima: require secure_boot rules in lockdown mode"
patch - http://kernsec.org/pipermail/linux-security-module-archive/201
7-October/003910.html.

The IMA "secure_boot" policy can be specified on the boot command line
as ima_policy="secure_boot".  It requires kernel modules, firmware,
kexec kernel image and the IMA custom policy to be signed.  In
lockdown mode, these rules are enabled by default and added to the
custom policy.

> On the other hand, I am not good on IMA. I have traced the code path
> in kimage_file_prepare_segments(). Looks that the READING_KEXEC_IMAGE
> doesn't show in selinux_kernel_read_file(). Where is the exact code
> in IMA for checking the signature when loading crash kernel file?

kernel_read_file_from_fd() calls the security_kernel_read_file() and
security_kernel_post_read_file() hooks, which call ima_read_file() and
ima_post_read_file() respectively.

Mimi