# kernel_lockdown

## 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.
    


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