TLDRVuln - Cybersecurity Vulnerabilities Made Simple

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

arm64: efi: Make efi_rt_lock a raw_spinlock

Running a rt-kernel base on 6.2.0-rc3-rt1 on an Ampere Altra outputs

the following:

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46

in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 9, name: kworker/u320:0

preempt_count: 2, expected: 0

RCU nest depth: 0, expected: 0

3 locks held by kworker/u320:0/9:

#0: ffff3fff8c27d128 ((wq_completion)efi_rts_wq){+.+.}-{0:0}, at: process_one_work (./include/linux/atomic/atomic-long.h:41)

#1: ffff80000861bdd0 ((work_completion)(&efi_rts_work.work)){+.+.}-{0:0}, at: process_one_work (./include/linux/atomic/atomic-long.h:41)

#2: ffffdf7e1ed3e460 (efi_rt_lock){+.+.}-{3:3}, at: efi_call_rts (drivers/firmware/efi/runtime-wrappers.c:101)

Preemption disabled at:

efi_virtmap_load (./arch/arm64/include/asm/mmu_context.h:248)

CPU: 0 PID: 9 Comm: kworker/u320:0 Tainted: G W 6.2.0-rc3-rt1

Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18

Workqueue: efi_rts_wq efi_call_rts

Call trace:

dump_backtrace (arch/arm64/kernel/stacktrace.c:158)

show_stack (arch/arm64/kernel/stacktrace.c:165)

dump_stack_lvl (lib/dump_stack.c:107 (discriminator 4))

dump_stack (lib/dump_stack.c:114)

__might_resched (kernel/sched/core.c:10134)

rt_spin_lock (kernel/locking/rtmutex.c:1769 (discriminator 4))

efi_call_rts (drivers/firmware/efi/runtime-wrappers.c:101)

[...]

This seems to come from commit ff7a167961d1 ("arm64: efi: Execute

runtime services from a dedicated stack") which adds a spinlock. This

spinlock is taken through:

efi_call_rts()

\-efi_call_virt()

\-efi_call_virt_pointer()

\-arch_efi_call_virt_setup()

Make 'efi_rt_lock' a raw_spinlock to avoid being preempted.

[ardb: The EFI runtime services are called with a different set of

translation tables, and are permitted to use the SIMD registers.

The context switch code preserves/restores neither, and so EFI

calls must be made with preemption disabled, rather than only

disabling migration.]