kernel_lockdown

KERNEL_LOCKDOWN(7)         Linux Programmer's Manual        KERNEL_LOCKDOWN(7)

NAME
       kernel_lockdown - kernel image access prevention feature

DESCRIPTION
       The  Kernel Lockdown feature is designed to prevent both direct and in-
       direct 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:

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

       o The use of direct PCI BAR access.

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

       o The use of the KD*IO console ioctls.

       o The use of the TIOCSSERIAL serial ioctl.

       o The alteration of MSR registers on x86.

       o The replacement of the PCMCIA CIS.

       o The overriding of ACPI tables.

       o The use of ACPI error injection.

       o The specification of the ACPI RDSP address.

       o The use of ACPI custom methods.

       Certain facilities are restricted:

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

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

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

       o Use  of  debugfs is not permitted as this allows a whole range of ac-
         tions including direct configuration of, access  to  and  driving  of
         hardware.

       o 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)