CVE-2026-90589

When CONFIG THREAD STACK MEM MAPPED is enabled, each thread stack is mapped into the kernel virtual address space with a guard page on either side, and the mapping is released during abort cleanup. k thread abort cleanup() in kernel/thread.c has two paths: a deferred one for self-abort, which stashes the mapping in thread cleanup stack addr/thread cleanup stack sz, and an immediate one for a thread aborted by some other thread. The immediate path called do thread cleanup(), which ignored its thread argument and only ever unmapped the stashed address — a value populated exclusively by the self-abort path. The mapped stack of a thread aborted by another thread was therefore never unmapped.

Every k thread abort() of a non-current thread leaks the thread's stack region plus its two guard pages from the kernel virtual address space. Threads that end by returning from their entry function take the working self-abort path, so the leak is specific to explicit cancellation — k thread abort(), pthread cancel(), osThreadTerminate(), or the kernel thread kill shell command. Both k thread create() and k thread abort() are system calls, so with CONFIG USERSPACE an unprivileged user-mode thread that has been granted a thread object and a user-capable stack object can drive the leak from user mode, consuming a kernel-side resource it cannot otherwise touch.

With CONFIG KERNEL VM SIZE defaulting to 8 MB, a few hundred create/abort cycles exhaust the runtime mapping region. k mem map phys guard() then returns NULL, and map thread stack() guards that only with ASSERT NO MSG(), which is compiled out of production builds; thread creation proceeds to write through a NULL-derived stack base and faults in kernel mode. The impact is a persistent denial of service — a kernel fatal error requiring a reboot — with no memory disclosure or corruption, and it is limited to configurations where memory-mapped thread stacks are enabled (x86 targets with X86 MMU and demand paging disabled, where the option is implied by default).