CVE-2021-29628

En FreeBSD versiones 13.0-STABLE anteriores a n245764-876ffe28796c, versiones 12.2-STABLE anteriores a r369857, versiones 13.0-RELEASE anteriores a p1 y versiones 12.2-RELEASE anteriores a p7, una llamada al sistema que desencadena un fallo podría causar que las protecciones SMAP sean deshabilitadas durante la llamada al sistema. Esta debilidad podría ser combinada con otros bugs del kernel para diseñar una explotación

The FreeBSD kernel enables SMAP during boot when the CPU reports that the SMAP capability is present. Subroutines such as copyin() and copyout() are responsible for disabling SMAP around the sections of code that perform user memory accesses. Such subroutines must handle page faults triggered when user memory is not mapped. The kernel's page fault handler checks the validity of the fault, and if it is indeed valid it will map a page and resume copying. If the fault is invalid, the fault handler returns control to a trampoline which aborts the operation and causes an error to be returned. In this second scenario, a bug in the implementation of SMAP support meant that SMAP would remain disabled until the thread returns to user mode. This bug may be used to bypass the protections provided by SMAP for the duration of a system call. It could thus be combined with other kernel bugs to craft an exploit.