[PATCH] irqchip/sifive-plic: avoid interrupt ID 0 handling during suspend/resume

[Lucas Zampieri]

To: linux-kernel at vger.kernel.org
Cc: Paul Walmsley <paul.walmsley at sifive.com>
Cc: Samuel Holland <samuel.holland at sifive.com>
Cc: stable at vger.kernel.org
Cc: linux-riscv at lists.infradead.org
Cc: Thomas Gleixner <tglx at linutronix.de>

According to the PLIC specification[1], global interrupt sources are
assigned small unsigned integer identifiers beginning at the value 1.
An interrupt ID of 0 is reserved to mean "no interrupt".

The current plic_irq_resume() and plic_irq_suspend() functions incorrectly
starts the loop from index 0, which could access the reserved interrupt ID
0 register space.
This fix changes the loop to start from index 1, skipping the reserved
interrupt ID 0 as per the PLIC specification.

This prevents potential undefined behavior when accessing the reserved
register space during suspend/resume cycles.

Fixes: e80f0b6a2cf3 ("irqchip/irq-sifive-plic: Add syscore callbacks for hibernation")
Co-developed-by: Jia Wang <wangjia at ultrarisc.com>
Signed-off-by: Jia Wang <wangjia at ultrarisc.com>
Signed-off-by: Lucas Zampieri <lzampier at redhat.com>

[1] https://github.com/riscv/riscv-plic-spec/releases/tag/1.0.0
---
 drivers/irqchip/irq-sifive-plic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index bf69a4802b71..1c2b4d2575ac 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -252,7 +252,7 @@ static int plic_irq_suspend(void)
 
 	priv = per_cpu_ptr(&plic_handlers, smp_processor_id())->priv;
 
-	for (i = 0; i < priv->nr_irqs; i++) {
+	for (i = 1; i < priv->nr_irqs; i++) {
 		__assign_bit(i, priv->prio_save,
 			     readl(priv->regs + PRIORITY_BASE + i * PRIORITY_PER_ID));
 	}
@@ -283,7 +283,7 @@ static void plic_irq_resume(void)
 
 	priv = per_cpu_ptr(&plic_handlers, smp_processor_id())->priv;
 
-	for (i = 0; i < priv->nr_irqs; i++) {
+	for (i = 1; i < priv->nr_irqs; i++) {
 		index = BIT_WORD(i);
 		writel((priv->prio_save[index] & BIT_MASK(i)) ? 1 : 0,
 		       priv->regs + PRIORITY_BASE + i * PRIORITY_PER_ID);
-- 
2.51.0