[PATCH] irqchip/gic-v4: Harden against bogus command line

[Mostafa Saleh <smostafa@google.com>]

When accidentally setting “kvm-arm.vgic_v4_enable=1” on the wrong
setup that has no MSI controller device tree node (it exists but
not used) and GICv4, it caused a panic as “gic_domain” is NULL and
the kernel attempted to access its ops.

Originally, I hit this on an older kernel, but was able to reproduce
it on upstream with Qemu by hacking this unreasonable setup.

[   33.145536] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000028
[   33.145658] Mem abort info:
[   33.145751]   ESR = 0x0000000096000006
...
[   33.154057] CPU: 1 UID: 0 PID: 295 Comm: lkvm-static Not tainted 7.1.0-rc4-ge3f15ad3970e #5 PREEMPT
[   33.156922] Hardware name: linux,dummy-virt (DT)
[   33.158780] pstate: 81402005 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[   33.160340] pc : __irq_domain_instantiate+0x1d4/0x578
[   33.162602] lr : __irq_domain_instantiate+0x1cc/0x578

Add a hardening check to avoid the NULL access, and fail the VM
creation in that case.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/irqchip/irq-gic-v4.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/irqchip/irq-gic-v4.c b/drivers/irqchip/irq-gic-v4.c
index 8455b4a5fbb0..7e39f7eae85f 100644
--- a/drivers/irqchip/irq-gic-v4.c
+++ b/drivers/irqchip/irq-gic-v4.c
@@ -159,6 +159,9 @@ int its_alloc_vcpu_irqs(struct its_vm *vm)
 {
 	int vpe_base_irq, i;
 
+	if (!gic_domain)
+		return -EINVAL;
+
 	vm->fwnode = irq_domain_alloc_named_id_fwnode("GICv4-vpe",
 						      task_pid_nr(current));
 	if (!vm->fwnode)
-- 
2.54.0.669.g59709faab0-goog