linux-kernel - [PATCH] irqchip/mips-gic: Don't overrun pcpu

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Message-ID: <1461234714-9975-1-git-send-email-paul.burton@imgtec.com>
Date:	Thu, 21 Apr 2016 11:31:54 +0100
From:	Paul Burton <paul.burton@...tec.com>
To:	<linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	"Marc Zyngier" <marc.zyngier@....com>
CC:	Paul Burton <paul.burton@...tec.com>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH] irqchip/mips-gic: Don't overrun pcpu_masks array

Commit 2a0787051182 ("irqchip/mips-gic: Use gic_vpes instead of
NR_CPUS") & commit 78930f09b940 ("irqchip/mips-gic: Clear percpu_masks
correctly when mapping") both introduce code which accesses gic_vpes
entries in the pcpu_masks array. However, this array has length NR_CPUS.
If NR_CPUS is less than gic_vpes (ie. the kernel supports use of less
CPUs than are present in the system) then we overrun the array, clobber
some other data & generally die pretty promptly.

Most notably this affects uniprocessor kernels running on any multicore
or multithreaded Malta with a GIC (ie. the vast majority of real Malta
boards).

Fix this by only accessing up to min(gic_vpes, NR_CPUS) entries in the
pcpu_masks array, preventing the array overrun.

Signed-off-by: Paul Burton <paul.burton@...tec.com>
Fixes: 2a0787051182 ("irqchip/mips-gic: Use gic_vpes instead of NR_CPUS")
Fixes: 78930f09b940 ("irqchip/mips-gic: Clear percpu_masks correctly when mapping")

---

 drivers/irqchip/irq-mips-gic.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-mips-gic.c b/drivers/irqchip/irq-mips-gic.c
index 94a30da..4dffccf 100644
--- a/drivers/irqchip/irq-mips-gic.c
+++ b/drivers/irqchip/irq-mips-gic.c
@@ -467,7 +467,7 @@ static int gic_set_affinity(struct irq_data *d, const struct cpumask *cpumask,
 	gic_map_to_vpe(irq, mips_cm_vp_id(cpumask_first(&tmp)));
 
 	/* Update the pcpu_masks */
-	for (i = 0; i < gic_vpes; i++)
+	for (i = 0; i < min(gic_vpes, NR_CPUS); i++)
 		clear_bit(irq, pcpu_masks[i].pcpu_mask);
 	set_bit(irq, pcpu_masks[cpumask_first(&tmp)].pcpu_mask);
 
@@ -707,7 +707,7 @@ static int gic_shared_irq_domain_map(struct irq_domain *d, unsigned int virq,
 	spin_lock_irqsave(&gic_lock, flags);
 	gic_map_to_pin(intr, gic_cpu_pin);
 	gic_map_to_vpe(intr, vpe);
-	for (i = 0; i < gic_vpes; i++)
+	for (i = 0; i < min(gic_vpes, NR_CPUS); i++)
 		clear_bit(intr, pcpu_masks[i].pcpu_mask);
 	set_bit(intr, pcpu_masks[vpe].pcpu_mask);
 	spin_unlock_irqrestore(&gic_lock, flags);
-- 
2.8.0