{"id":99293,"date":"2021-02-28T10:22:45","date_gmt":"2021-02-28T08:22:45","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/v-yadro-linux-5-12-prinyata-podsistema-kfence-dlya-vyyavleniya-oshibok-pri-rabote-s-pamyatyu"},"modified":"2021-02-28T10:22:45","modified_gmt":"2021-02-28T08:22:45","slug":"v-yadro-linux-5-12-prinyata-podsistema-kfence-dlya-vyyavleniya-oshibok-pri-rabote-s-pamyatyu","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/v-yadro-linux-5-12-prinyata-podsistema-kfence-dlya-vyyavleniya-oshibok-pri-rabote-s-pamyatyu","title":{"rendered":"KFence Subsystem for Memory Error Detection Accepted in Linux Kernel 5.12","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"
The in-development Linux kernel 5.12 includes the implementation of the KFence (Kernel Electric Fence) mechanism, which checks memory operations by detecting buffer overflows, accesses to freed memory, and other similar errors. <\/p>\n
This functionality was already present in the kernel in the form of the KASAN (kernel address sanitizer) build option (using Address Sanitizer in modern gcc and clang) \u2014 however, it was primarily positioned for debugging purposes. The KFence subsystem differs from KASAN in its high speed, allowing this capability to be utilized even in kernels running in production systems. <\/p>\n
Using it in production systems will enable the detection of memory operation errors that do not manifest during test runs and only appear under heavy workloads or prolonged operation (with high uptime). Additionally, applying KFence in production systems will significantly increase the number of machines involved in testing the kernel's memory operations. <\/p>\n
Minimal overhead, independent of load, is achieved in KFence by inserting guard pages into the heap at fixed intervals. After the expiration of the current guard interval, KFence adds another guard page from the KFence object pool through the standard memory allocation system (SLAB or SLUB allocator) and starts a new time counter. Each KFence object is placed on a separate memory page, with the memory pages along the left and right edges forming the guard pages, the size of which is selected randomly. <\/p>\n
Thus, pages with objects are separated from one another by protection pages, which are configured to trigger a \"page fault\" on any access. To detect out-of-bounds write operations within pages containing objects, additional \"red zones\" based on patterns are used, occupying memory that is not utilized by objects and remaining after memory page size alignment. \u2014+\u2014\u2014\u2014\u2014+\u2014\u2014\u2014+\u2014\u2014\u2014\u2014+ : O | xxxxxxxxx | | xxxxxxxxx | B : | xxxxxxxxx | : B | xxxxxxxxx | | x GUARD x | J : RED- | x GUARD x | RED- : J | x GUARD x | | xxxxxxxxx | E : ZONE | xxxxxxxxx | ZONE : E | xxxxxxxxx | | xxxxxxxxx | C : | xxxxxxxxx | : C | xxxxxxxxx | | xxxxxxxxx | T : | xxxxxxxxx | : T | xxxxxxxxx | \u2014+\u2014\u2014\u2014\u2014+\u2014\u2014\u2014+\u2014\u2014\u2014\u2014+ <\/p>\n
In the event of attempting to access an area outside the buffer boundaries, the operation touches the protection page, which leads to the generation of a \"page fault\" that is intercepted by KFence, logging information about the detected issue. By default, KFence does not block the error and only logs a warning, but there is a configuration option called \"panic_on_warn\" that allows the kernel to switch to a crash state (panic) upon error detection. \n Source: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"