RISC-V: KVM: Fix use-after-free in kvm_riscv_aia_aplic_has_attr()

Fuzzer reports a KASAN use-after-free bug triggered by a race
between KVM_HAS_DEVICE_ATTR and KVM_SET_DEVICE_ATTR ioctls on
the AIA device. The root cause is that aia_has_attr() invokes
kvm_riscv_aia_aplic_has_attr() without holding dev->kvm->lock, while
a concurrent aia_set_attr() may call aia_init() under that lock. When
aia_init() fails after kvm_riscv_aia_aplic_init() has succeeded, it
calls kvm_riscv_aia_aplic_cleanup() in its fail_cleanup_imsics path,
which frees both aplic_state and aplic_state->irqs. The concurrent
has_attr path can then dereference the freed aplic->irqs in
aplic_read_pending():
irqd = &aplic->irqs[irq]; /* UAF here */

KASAN report:
BUG: KASAN: slab-use-after-free in aplic_read_pending
arch/riscv/kvm/aia_aplic.c:119 [inline]
BUG: KASAN: slab-use-after-free in aplic_read_pending_word
arch/riscv/kvm/aia_aplic.c:351 [inline]
BUG: KASAN: slab-use-after-free in aplic_mmio_read_offset
arch/riscv/kvm/aia_aplic.c:406
Read of size 8 at addr ff600000ba965d58 by task 9498
Call Trace:
aplic_read_pending arch/riscv/kvm/aia_aplic.c:119 [inline]
aplic_read_pending_word arch/riscv/kvm/aia_aplic.c:351 [inline]
aplic_mmio_read_offset arch/riscv/kvm/aia_aplic.c:406
kvm_riscv_aia_aplic_has_attr arch/riscv/kvm/aia_aplic.c:566
aia_has_attr arch/riscv/kvm/aia_device.c:469
allocated by task 9473:
kvm_riscv_aia_aplic_init arch/riscv/kvm/aia_aplic.c:583
aia_init arch/riscv/kvm/aia_device.c:248 [inline]
aia_set_attr arch/riscv/kvm/aia_device.c:334
freed by task 9473:
kvm_riscv_aia_aplic_cleanup arch/riscv/kvm/aia_aplic.c:644
aia_init arch/riscv/kvm/aia_device.c:292 [inline]
aia_set_attr arch/riscv/kvm/aia_device.c:334

Fix this race by acquiring dev->kvm->lock in aia_has_attr() before
calling kvm_riscv_aia_aplic_has_attr(), consistent with the locking
pattern used in aia_get_attr() and aia_set_attr().

Fixes: 289a007b98b06d ("RISC-V: KVM: Expose APLIC registers as attributes of AIA irqchip")
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260302132703.1721415-1-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>