[PATCH v3 2/4] xen/arm: validate IRQs before descriptor lookup

[Mykola Kvach <mykola_kvach@xxxxxxxx>]

GICv3 eSPI support makes nr_irqs span the architectural INTID namespace
through ESPI_MAX_INTID, but descriptor storage is sparse. local_irq_desc[]
and irq_desc[] cover INTIDs below NR_IRQS, while espi_desc[] covers eSPIs.
INTIDs 1024 through 4095 have no backing descriptors.

Validation based only on nr_irqs accepts an INTID in this gap.
__irq_to_desc() then indexes beyond irq_desc[], and callers may lock or
update unrelated Xen memory.

Reject INTIDs that the GIC reports as unimplemented in setup_irq() before
looking up a descriptor. irq_set_spi_type() can run before the implemented
GIC line counts are available, so validate descriptor-backed ranges there
before looking up a descriptor.

Assert the regular descriptor bound in __irq_to_desc() so direct callers
cannot silently index the sparse gap in debug builds.

Fixes: 98f7060b9ed5 ("xen/arm/irq: add handling for IRQs in the eSPI range")
Signed-off-by: Mykola Kvach <mykola_kvach@xxxxxxxx>
---
Changes in v3:
- Add the requested bound assertion and retain the SPI-only comment.

Changes in v2:
- Validate descriptor-backed ranges in irq_set_spi_type().
- Validate implemented GIC lines in setup_irq().
- Preserve is_espi() validation with CONFIG_GICV3_ESPI disabled.
---
 xen/arch/arm/irq.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/irq.c b/xen/arch/arm/irq.c
index 73e58a5108..bf14180f97 100644
--- a/xen/arch/arm/irq.c
+++ b/xen/arch/arm/irq.c
@@ -23,6 +23,12 @@ const unsigned int nr_irqs = IS_ENABLED(CONFIG_GICV3_ESPI) ?
                                         (ESPI_MAX_INTID + 1) :
                                         NR_IRQS;
 
+static bool irq_has_desc(unsigned int irq)
+{
+    return irq < NR_IRQS ||
+           (IS_ENABLED(CONFIG_GICV3_ESPI) && is_espi(irq));
+}
+
 static unsigned int local_irqs_type[NR_LOCAL_IRQS];
 static DEFINE_SPINLOCK(local_irqs_type_lock);
 
@@ -76,7 +82,6 @@ static int __init init_espi_data(void)
     return 0;
 }
 #else
-
 static int __init init_espi_data(void)
 {
     return 0;
@@ -95,6 +100,8 @@ struct irq_desc *__irq_to_desc(unsigned int irq)
         return espi_to_desc(irq);
 #endif
 
+    ASSERT(irq < NR_IRQS);
+
     return &irq_desc[irq-NR_LOCAL_IRQS];
 }
 
@@ -416,6 +423,9 @@ int setup_irq(unsigned int irq, unsigned int irqflags, 
struct irqaction *new)
     struct irq_desc *desc;
     bool disabled;
 
+    if ( !gic_is_valid_line(irq) )
+        return -EINVAL;
+
     desc = irq_to_desc(irq);
 
     spin_lock_irqsave(&desc->lock, flags);
@@ -647,13 +657,21 @@ static bool irq_validate_new_type(unsigned int curr, 
unsigned int new)
 int irq_set_spi_type(unsigned int spi, unsigned int type)
 {
     unsigned long flags;
-    struct irq_desc *desc = irq_to_desc(spi);
+    struct irq_desc *desc;
     int ret = -EBUSY;
 
-    /* This function should not be used for other than SPIs */
-    if ( spi < NR_LOCAL_IRQS )
+    /*
+     * This function should not be used for other than SPIs.
+     *
+     * The implemented GIC line counts are not available when early
+     * callers configure IRQ types. Check descriptor storage here; setup_irq()
+     * validates the implemented line before the interrupt is used.
+     */
+    if ( spi < NR_LOCAL_IRQS || !irq_has_desc(spi) )
         return -EINVAL;
 
+    desc = irq_to_desc(spi);
+
     spin_lock_irqsave(&desc->lock, flags);
 
     if ( !irq_validate_new_type(desc->arch.type, type) )
-- 
2.43.0