NAME

       kernel_lockdown - kernel image access prevention feature

DESCRIPTION

       The  Kernel  Lockdown  feature is designed to prevent both direct and indirect access to a running kernel
       image, attempting to protect against unauthorized modification of the kernel image and to prevent  access
       to security and cryptographic data located in kernel memory, whilst still permitting driver modules to be
       loaded.

       If  a  prohibited  or  restricted  feature is accessed or used, the kernel will emit a message that looks
       like:

               Lockdown: X: Y is restricted, see man kernel_lockdown.7

       where X indicates the process name and Y indicates what is restricted.

       On an EFI-enabled x86 or arm64 machine, lockdown will be automatically enabled if the system boots in EFI
       Secure Boot mode.

   Coverage
       When lockdown is in effect, a number of features  are  disabled  or  have  their  use  restricted.   This
       includes special device files and kernel services that allow direct access of the kernel image:

              /dev/mem
              /dev/kmem
              /dev/kcore
              /dev/ioports
              BPF
              kprobes

       and the ability to directly configure and control devices, so as to prevent the use of a device to access
       or modify a kernel image:

       • The  use  of  module parameters that directly specify hardware parameters to drivers through the kernel
         command line or when loading a module.

       • The use of direct PCI BAR access.

       • The use of the ioperm and iopl instructions on x86.

       • The use of the KD*IO console ioctls.

       • The use of the TIOCSSERIAL serial ioctl.

       • The alteration of MSR registers on x86.

       • The replacement of the PCMCIA CIS.

       • The overriding of ACPI tables.

       • The use of ACPI error injection.

       • The specification of the ACPI RDSP address.

       • The use of ACPI custom methods.

       Certain facilities are restricted:

       • Only validly signed modules may be loaded (waived if the module file being loaded is vouched for by IMA
         appraisal).

       • Only validly signed binaries may be kexec'd (waived if the binary image file to be executed is  vouched
         for by IMA appraisal).

       • Unencrypted  hibernation/suspend  to  swap are disallowed as the kernel image is saved to a medium that
         can then be accessed.

       • Use of debugfs is not permitted as this allows a whole range of actions including direct  configuration
         of, access to and driving of hardware.

       • IMA  requires  the addition of the "secure_boot" rules to the policy, whether or not they are specified
         on the command line, for both the built-in and custom policies in secure boot lockdown mode.

VERSIONS

       The Kernel Lockdown feature was added in Linux 5.4.

NOTES

       The Kernel Lockdown feature is enabled by CONFIG_SECURITY_LOCKDOWN_LSM.   The  lsm=lsm1,...,lsmN  command
       line  parameter  controls  the sequence of the initialization of Linux Security Modules.  It must contain
       the string lockdown to enable the Kernel  Lockdown  feature.   If  the  command  line  parameter  is  not
       specified,  the initialization falls back to the value of the deprecated security= command line parameter
       and further to the value of CONFIG_LSM.

COLOPHON

       This page is part of release 5.10 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       https://www.kernel.org/doc/man-pages/.

Linux                                              2020-11-01                                 KERNEL_LOCKDOWN(7)