KVM: x86: protect KVM_CREATE_PIT/KVM_CREATE_PIT2 with kvm->lock
The syzkaller folks reported a NULL pointer dereference that seems
to be cause by a race between KVM_CREATE_IRQCHIP and KVM_CREATE_PIT2.
The former takes kvm->lock (except when registering the devices,
which needs kvm->slots_lock); the latter takes kvm->slots_lock only.
Change KVM_CREATE_PIT2 to follow the same model as KVM_CREATE_IRQCHIP.
Testcase:
#include <pthread.h>
#include <linux/kvm.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
#include <sys/syscall.h>
#include <unistd.h>
long r[23];
void* thr1(void* arg)
{
struct kvm_pit_config pitcfg = { .flags = 4 };
switch ((long)arg) {
case 0: r[2] = open("/dev/kvm", O_RDONLY|O_ASYNC); break;
case 1: r[3] = ioctl(r[2], KVM_CREATE_VM, 0); break;
case 2: r[4] = ioctl(r[3], KVM_CREATE_IRQCHIP, 0); break;
case 3: r[22] = ioctl(r[3], KVM_CREATE_PIT2, &pitcfg); break;
}
return 0;
}
int main(int argc, char **argv)
{
long i;
pthread_t th[4];
memset(r, -1, sizeof(r));
for (i = 0; i < 4; i++) {
pthread_create(&th[i], 0, thr, (void*)i);
if (argc > 1 && rand()%2) usleep(rand()%1000);
}
usleep(20000);
return 0;
}
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index a4bf5b4..5fb6c62 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -645,7 +645,6 @@
.write = speaker_ioport_write,
};
-/* Caller must hold slots_lock */
struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
{
struct kvm_pit *pit;
@@ -690,6 +689,7 @@
kvm_pit_set_reinject(pit, true);
+ mutex_lock(&kvm->slots_lock);
kvm_iodevice_init(&pit->dev, &pit_dev_ops);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, KVM_PIT_BASE_ADDRESS,
KVM_PIT_MEM_LENGTH, &pit->dev);
@@ -704,12 +704,14 @@
if (ret < 0)
goto fail_register_speaker;
}
+ mutex_unlock(&kvm->slots_lock);
return pit;
fail_register_speaker:
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &pit->dev);
fail_register_pit:
+ mutex_unlock(&kvm->slots_lock);
kvm_pit_set_reinject(pit, false);
kthread_stop(pit->worker_task);
fail_kthread: