In the Linux kernel, the following vulnerability has been resolved:
ARM: 9483/1: select HAVE_POSIX_CPU_TIMERS_TASK_WORK
Commit c6e61c06d606 (“ARM: 9463/1: Allow to enable RT”) enabled PREEMPT_RT
on ARM but did not select HAVE_POSIX_CPU_TIMERS_TASK_WORK. This leaves
CONFIG_POSIX_CPU_TIMERS_TASK_WORK disabled, so CPU timers expire in hard
IRQ context.
On PREEMPT_RT this makes run_posix_cpu_timers() take the sleeping
sighand->siglock:
BUG: sleeping function called from invalid context at spinlock_rt.c:48
rt_spin_lock from lock_task_sighand
lock_task_sighand from run_posix_cpu_timers
run_posix_cpu_timers from update_process_times
ARM handles TIF_NOTIFY_RESUME on all return-to-user paths, including v7-M.
ARM32 KVM host support was removed by commit 541ad0150ca4 (“arm: Remove
32bit KVM host support”), so the select need not be conditional on KVM.
Select it to defer POSIX CPU timer expiry to task context.
Reproduced with setrlimit(RLIMIT_CPU, …) and a busy loop. The same path
is used by setitimer(ITIMER_PROF or ITIMER_VIRTUAL) and POSIX CPU timers
created with timer_create().
