Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  powerpc/time: Remove redundant preempt_disable|enable() calls from arch_irq_work_raise()  A kernel panic is observed when handling machine check exceptions from real mode.    BUG: Unable to handle kernel data access on read at 0xc00000006be21300   Oops: Kernel access of bad area, sig: 11 [#1]   MSR:  8000000000001003 <SF,ME,RI,LE>  CR: 88222248  XER: 00000005   CFAR: c00000000003ffc4 DAR: c00000006be21300 DSISR: 40000000 IRQMASK: 0   NIP [c000000000029e40] arch_irq_work_raise+0x10/0x70   LR [c00000000003ffc8] machine_check_queue_event+0xa8/0x150   Call Trace:   [c0000000179d3c70] [c00000000003ff64] machine_check_queue_event+0x44/0x150   [c0000000179d3d30] [c0000000000084e0] machine_check_early_common+0x1f0/0x2c0  The crash occurs because arch_irq_work_raise() calls preempt_disable() from machine check exception (MCE) handlers running in real mode. In this context, accessing the preempt_count can fault, leading to the panic.  The preempt_disable()/preempt_enable() pair in arch_irq_work_raise() was originally added by commit 0fe1ac48bef0 ("powerpc/perf_event: Fix oops due to perf_event_do_pending call") to avoid races while raising irq work from exception context.  Later, commit 471ba0e686cb ("irq_work: Do not raise an IPI when queueing work on the local CPU") added preemption protection in irq_work_queue() path, while commit 20b876918c06 ("irq_work: Use per cpu atomics instead of regular atomics") added equivalent protection in irq_work_queue_on() before reaching arch_irq_work_raise():    irq_work_queue() / irq_work_queue_on()     -> preempt_disable()       -> __irq_work_queue_local()         -> irq_work_raise()           -> arch_irq_work_raise()  As a result, callers other than mce_irq_work_raise() already execute with preemption disabled, making the additional preempt_disable()/preempt_enable() pair in arch_irq_work_raise() redundant.  The arch_irq_work_raise() function executes in NMI context when called from MCE handler. Hence we will not be preempted or scheduled out since we are in NMI context with MSR[EE]=0. Therefore, it is safe to remove the preempt_disable()/preempt_enable() calls from here.  Remove it to avoid accessing preempt_count from real mode context.  [Maddy: Fixed the commit title]