CVE-2022-49090

In the Linux kernel, the following vulnerability has been resolved:

arch/arm64: Fix topology initialization for core scheduling

Arm64 systems rely on storecputopology() to call updatesiblingsmasks() to transfer the toplogy to the various cpu masks. This needs to be done before the call to notifycpustarting() which tells the scheduler about each cpu found, otherwise the core scheduling data structures are setup in a way that does not match the actual topology.

With smt_mask not setup correctly we bail on cpumask_weight(smt_mask) == 1 for !leaders in:

notifycpustarting() cpuhpinvokecallbackrange() schedcpustarting() schedcorecpustarting()

which leads to rq->core not being correctly set for !leader-rq's.

Without this change stress-ng (which enables core scheduling in its prctl tests in newer versions -- i.e. with PRSCHEDCORE support) causes a warning and then a crash (trimmed for legibility):

[ 1853.805168] ------------[ cut here ]------------ [ 1853.809784] taskrq(b)->core != rq->core [ 1853.809792] WARNING: CPU: 117 PID: 0 at kernel/sched/fair.c:11102 cfsprioless+0x1b4/0x1c4 ... [ 1854.015210] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010 ... [ 1854.231256] Call trace: [ 1854.233689] picknexttask+0x3dc/0x81c [ 1854.237512] _schedule+0x10c/0x4cc [ 1854.240988] schedule_idle+0x34/0x54