[PATCH v4 2/7] PCI: xilinx-nwl: Fix off-by-one in IRQ handler

[Sean Anderson <sean.anderson@linux.dev>]

MSGF_LEG_MASK is laid out with INTA in bit 0, INTB in bit 1, INTC in bit
2, and INTD in bit 3. Hardware IRQ numbers start at 0, and we register
PCI_NUM_INTX irqs. So to enable INTA (aka hwirq 0) we should set bit 0.
Remove the subtraction of one.

This bug would cause legacy interrupts not to be delivered, as enabling
INTB would actually enable INTA, and enabling INTA wouldn't enable
anything at all. It is likely that this got overlooked for so long since
most PCIe hardware uses MSIs. This fixes the following UBSAN error:

UBSAN: shift-out-of-bounds in ../drivers/pci/controller/pcie-xilinx-nwl.c:389:11
shift exponent 18446744073709551615 is too large for 32-bit type 'int'
CPU: 1 PID: 61 Comm: kworker/u10:1 Not tainted 6.6.20+ #268
Hardware name: xlnx,zynqmp (DT)
Workqueue: events_unbound deferred_probe_work_func
Call trace:
dump_backtrace (arch/arm64/kernel/stacktrace.c:235)
show_stack (arch/arm64/kernel/stacktrace.c:242)
dump_stack_lvl (lib/dump_stack.c:107)
dump_stack (lib/dump_stack.c:114)
__ubsan_handle_shift_out_of_bounds (lib/ubsan.c:218 lib/ubsan.c:387)
nwl_unmask_leg_irq (drivers/pci/controller/pcie-xilinx-nwl.c:389 (discriminator 1))
irq_enable (kernel/irq/internals.h:234 kernel/irq/chip.c:170 kernel/irq/chip.c:439 kernel/irq/chip.c:432 kernel/irq/chip.c:345)
__irq_startup (kernel/irq/internals.h:239 kernel/irq/chip.c:180 kernel/irq/chip.c:250)
irq_startup (kernel/irq/chip.c:270)
__setup_irq (kernel/irq/manage.c:1800)
request_threaded_irq (kernel/irq/manage.c:2206)
pcie_pme_probe (include/linux/interrupt.h:168 drivers/pci/pcie/pme.c:348)
<snip>

Fixes: 9a181e1093af ("PCI: xilinx-nwl: Modify IRQ chip for legacy interrupts")
Cc: <stable@vger.kernel.org>
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
---

Changes in v4:
- Explain likely effects of the off-by-one error
- Trim down UBSAN backtrace

Changes in v3:
- Expand commit message

 drivers/pci/controller/pcie-xilinx-nwl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pcie-xilinx-nwl.c b/drivers/pci/controller/pcie-xilinx-nwl.c
index 0408f4d612b5..437927e3bcca 100644
--- a/drivers/pci/controller/pcie-xilinx-nwl.c
+++ b/drivers/pci/controller/pcie-xilinx-nwl.c
@@ -371,7 +371,7 @@ static void nwl_mask_intx_irq(struct irq_data *data)
 	u32 mask;
 	u32 val;
 
-	mask = 1 << (data->hwirq - 1);
+	mask = 1 << data->hwirq;
 	raw_spin_lock_irqsave(&pcie->leg_mask_lock, flags);
 	val = nwl_bridge_readl(pcie, MSGF_LEG_MASK);
 	nwl_bridge_writel(pcie, (val & (~mask)), MSGF_LEG_MASK);
@@ -385,7 +385,7 @@ static void nwl_unmask_intx_irq(struct irq_data *data)
 	u32 mask;
 	u32 val;
 
-	mask = 1 << (data->hwirq - 1);
+	mask = 1 << data->hwirq;
 	raw_spin_lock_irqsave(&pcie->leg_mask_lock, flags);
 	val = nwl_bridge_readl(pcie, MSGF_LEG_MASK);
 	nwl_bridge_writel(pcie, (val | mask), MSGF_LEG_MASK);
-- 
2.35.1.1320.gc452695387.dirty


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