Kernel module binary
In computinga loadable kernel module LKM is an object file that contains kernel module binary to extend the running kernelor so-called base kernelof an operating system.
When the functionality provided by a LKM is no longer required, it can be unloaded in order to free memory and other resources. Without loadable kernel modules, an operating system would have to include all possible anticipated kernel module binary already compiled directly into the base kernel. Much of that functionality would reside in memory without being used, wasting memory, and would require that users rebuild and reboot the base kernel every time they require new functionality.
Most operating systems supporting loadable kernel modules will include modules to support most desired functionality. One minor criticism of preferring a modular kernel over a static kernel is the so-called fragmentation penalty. The base kernel kernel module binary always unpacked into real contiguous memory by kernel module binary setup routines; thus, the base kernel code kernel module binary never fragmented.
Once the system is in a state in which modules may be inserted, for example once the filesystems have been mounted that contain the modules, it is likely that any new kernel code insertion will cause the kernel to become fragmented, thereby introducing a minor performance penalty by using more TLB entries, causing more TLB misses. Loadable kernel modules in Linux are loaded and unloaded by the modprobe command. In emergency cases, when the system fails to boot due to e.
In the opinion of Linux maintainers, LKM are derived works of the kernel [ citation needed ]. Loading a proprietary or non-GPL-compatible LKM will set a 'taint' flag  in the running kernel—meaning that any problems or bugs experienced will be less likely to be investigated by the maintainers. Kernel module binary kernel modules usually have the extension. Once the machine has booted, they may be loaded with the kldload command, unloaded with kldunloadand listed with kldstat.
Some loadable kernel modules in macOS can be loaded automatically. Loadable kernel modules can also be loaded by the kextload command.
They can be listed by the kextstat command. Loadable kernel modules are located in bundles with the extension. NLMs may reside in any valid search path assigned on the NetWare server, and they have. NLM as the file name extension. A downloadable kernel module DKM type project can be created to generate a ".
This downloadable kernel module can be unloaded using "unld" command. This means that there are differences in internal structure and function between different kernel versions, which can cause compatibility problems. In an attempt to combat those problems, symbol versioning data is placed within the. This versioning information can be compared with that of the running kernel before loading a kernel module binary if the versions are incompatible, the module will not be loaded. For example, FreeBSD kernel modules compiled against kernel version 6.
However, they are not compatible with other major versions and must be recompiled for use with FreeBSD 7. While loadable kernel modules are a convenient method of modifying the running kernel, this can be abused by attackers on a compromised system to prevent detection of their processes or filesallowing them to maintain control over the system. Many rootkits make use of LKMs in this way.
Note that on most operating systems modules do not help privilege elevation in any way, as elevated privilege is required to load a LKM; they merely make it easier for the attacker to hide the break-in. This makes the security very similar to a monolithic kernel. If an attacker can change the initramfs, they kernel module binary change the kernel binary. In OS X Yosemite and later releases, a kernel extension has to be code-signed with a developer certificate that holds a particular "entitlement" for this.
Such a developer certificate is only kernel module binary by Apple on request and not automatically given to Apple Developer members. This feature, called "kext signing", is enabled by default and it instructs the kernel to stop booting if unsigned kernel extensions are present. In older kernel module binary of macOS, or if kext signing is disabled, a loadable kernel module in a kernel extension bundle can be kernel module binary by non-root users if the OSBundleAllowUserLoad property is set to True in the bundle's property list.
Kernel modules can optionally have a cryptographic signature ELF section which is verified on load depending on the Verified Boot policy settings. Userspace initiated kernel module loading is only possible from the Trusted Path when the system is running with the Immutable Global Zone feature enabled. From Wikipedia, the free encyclopedia. Archived from the original on May 4, Retrieved May 5, Archived from the original on March 6, Archived from the original on Archived from the original on November 2, Retrieved October 30, Retrieved Kernel module binary 4, Archived from the original on August 17, Retrieved September 29, Archived from the original on September 26, Retrieved September 27, Device driver Loadable kernel module Microkernel User space.
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The kernel module signing facility cryptographically signs modules kernel module binary installation and then checks the signature upon loading the module. This allows increased kernel kernel module binary by disallowing the loading of unsigned modules or modules signed with an invalid key. Module signing increases security by making it harder to load a malicious module into the kernel. The module signature checking is done by the kernel so that it is not necessary to have trusted userspace bits.
This facility uses X. The signatures are not themselves encoded in any industrial standard type. The facility currently only supports the RSA kernel module binary key encryption standard though it is pluggable and permits others to be used. The module signing facility is enabled by going to the Enable Loadable Module Support section of the kernel configuration and turning on:. This specifies how the kernel should deal with a module that has a signature for which the key is not known or a module that is unsigned.
If this is off ie. If this is on ie. All other modules will generate an error. Irrespective of the setting here, if the module has a signature block that cannot be parsed, it will be rejected out of hand.
If this is off, then the modules must be signed manually using:. Which hash algorithm should modules be signed with? This presents a choice of which hash algorithm the installation phase will sign the modules with:. The algorithm selected here will also be built into the kernel rather than being a module so that modules signed with that algorithm can kernel module binary their signatures checked without causing a dependency loop. The string provided should identify a file containing both a private key and its corresponding X.
This option can be set to the filename of a PEM-encoded file containing additional certificates which will be included in kernel module binary system keyring by default. Note that kernel module binary module signing adds a dependency on the OpenSSL devel packages to the kernel build processes for the tool that does the signing. Cryptographic keypairs are required to generate and check signatures. A private key is used to generate a signature and the corresponding public key is used to check it.
The private key is only needed during the build, after which it can be deleted or stored securely. The public key gets built into the kernel so that it can be used to check the signatures as the modules are loaded. Kernel module binary notably, in the x The kernel contains a ring of public keys that can be viewed by root.
Further, the architecture code may take public keys from a hardware store and add those in also e. Note, however, that the kernel will only permit keys to be added to.
The script requires 4 arguments:. A signed module has a digital signature simply appended at the end. Note the entire module is the signed payload, including any and all debug information present at the time of signing. The signature checking is all done within the kernel.
Otherwise, it will also load modules that are unsigned. Any module for which the kernel has a key, but which proves to have a signature mismatch will not be permitted to load. Since the private key is used to sign modules, viruses and malware could use the private key to sign modules and compromise the operating system.
The private key must be either destroyed or moved to a secure location and not kept in the root node of the kernel source tree. If you kernel module binary the same private key to sign modules for multiple kernel configurations, you must ensure that the module version information is sufficient to prevent loading a module into a different kernel. The Linux Kernel 4. If this is off, then the modules must be signed manually using: The script requires 4 arguments: The hash algorithm e.
Any kernel module binary that has an unparseable kernel module binary will be rejected.
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