arm64: Skip preemption when exiting an NMI

hulk inclusion
category: feature
bugzilla: 9291
CVE: NA

ported from https://lore.kernel.org/patchwork/patch/1037481/

--------------------------------

Handling of an NMI should not set any TIF flags. For NMIs received from
EL0 the current exit path is safe to use.

However, an NMI received at EL1 could have interrupted some task context
that has set the TIF_NEED_RESCHED flag. Preempting a task should not
happen as a result of an NMI.

Skip preemption after handling an NMI from EL1.
Signed-off-by: NJulien Thierry <julien.thierry@arm.com>
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NWei Li <liwei391@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/arm64/kernel/entry.S

@@ -637,7 +637,15 @@ el1_irq:
 
 #ifdef CONFIG_PREEMPT
 	ldr	w24, [tsk, #TSK_TI_PREEMPT]	// get preempt count
-	cbnz	w24, 1f				// preempt count != 0
+alternative_if ARM64_HAS_IRQ_PRIO_MASKING
+	/*
+	 * DA_F were cleared at start of handling. If anything is set in DAIF,
+	 * we come back from an NMI, so skip preemption
+	 */
+	mrs	x0, daif
+	orr	w24, w24, w0
+alternative_else_nop_endif
+	cbnz	w24, 1f				// preempt count != 0 || NMI return path
 	ldr	x0, [tsk, #TSK_TI_FLAGS]	// get flags
 	tbz	x0, #TIF_NEED_RESCHED, 1f	// needs rescheduling?
 	bl	el1_preempt