Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  sched/cache: Decouple sched_cache_group from mm to fix UAF  Currently the sched cache grouping is by mm and the scheduling statistics sched_cache_stat lives in the mm structure.  This ties the life cycle of scheduling stats with mm.  In account_mm_sched(), the scheduling stats are accessed by task->mm->sc_stat.  However, a task may be switching mm on one CPU when another CPU is running account_mm_sched(), and possibly accessing the old mm that was freed.  This problem was found when running tests with KASAN by Hyunwoo:    https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/  Instead of serializing the mm access by introducing extra acquisition of rq lock in the mm free path, extract sched_cache_stat from mm_struct, rename it as sched_cache_group and manage its life cycle apart from mm_struct with its own ref counting.  This allows us in the next patch access sched_cache_group directly from task, and add a refcount on sched_cache_group when a task links to it. This prevents the use after free issue when accessing stale and released old mm and its sched cache stat a task switches to a new mm while account_mm_sched() is done elsewhere.  The other benefit of this restructure is in the future, the grouping of tasks to a LLC would have the flexibility to be associated with a user defined grouping, or cgroup, cookie group, numa_group or others instead of just with a single mm address space.  Rename sched_cache_stat to sched_cache_group and turn it into a refcounted object allocated from mm_struct.  The mm_struct now holds a pointer (sched_cache_grp) to this object instead of embedding it.