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

[Mimi Zohar]

On Sat, 2017-10-28 at 16:34 +0800, joeyli wrote:
> On Fri, Oct 27, 2017 at 03:32:26PM -0400, Mimi Zohar wrote:
> > On Thu, 2017-10-26 at 10:17 -0400, Mimi Zohar wrote:
> > > 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@xxxxxxxxx>
> > > > > > 
> > > > > > 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. ÂAn additional patch could force
> > > > > these rules to be added to the custom policy, if lockdown is enabled.
> > > > > ÂThis 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. ÂThanks! ÂRemember is_ima_appraise_enabled() is
> > > dependent on the "ima: require secure_boot rules in lockdown mode"
> > > patch -Âhttp://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". ÂIt requires kernel modules, firmware,
> > > kexec kernel image and the IMA custom policy to be signed. ÂIn
> > > 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.
> > 
> > Hm, with "lockdown" enabled on the boot command line, I'm now able to
> > do the kexec load, but not the unload.  :/ Â After the kexec load with
> 
> I have tried on Qemu with OVMF, I can load and unload second kernel by
> kexec tool (on openSUSE is in kexec-tools RPM):  
> 
> # kexec -u -s

Thanks, I left off the "-s" option, causing it to fail. ÂThis is the
correct behavior. ÂSo both with/without the "-s" option are working
properly.

> I add -s for using kexec-load-file, and I signed kernel by pesign.
> 
> > the "--reuse-cmdline" option, the system reboots, but isn't in
> > "lockdown" mode.
> >
> 
> Either enabling secure boot in EFI firmware or using _lockdown_ kernel
> parameter, the second kernel can be locked down on my OVMF VM.
> 
> I used following commands:
> 
> # kexec -s -l /boot/vmlinuz-4.14.0-rc2-default+ --append="$(cat /proc/cmdline)" --initrd=/boot/initrd-4.14.0-rc2-default+
> # umount -a; mount -o remount,ro /I'
> # kexec -e
> 
> The kernel source is from David's linux-fs git with lockdown-20171026 tag.
> The kernel is also signed by pesign.

Yes, based on the patches in David's tree, "lockdown" is being carried
to the target OS properly.

Mimi