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    SubjectRe: [PATCH 07/27] kexec_file: Disable at runtime if securelevel has been set
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    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@gmail.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.
    > >
    > > Hm, with "lockdown" enabled on the boot command line, I'm now able to
    > > do the kexec load, but not the unload. :/   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.  This is the
    correct behavior.  So 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

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