Messages in this thread | | | Subject | Re: [PATCH v4 5/7] s390: ap: implement PAPQ AQIC interception in kernel | From | Pierre Morel <> | Date | Fri, 1 Mar 2019 10:35:48 +0100 |
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On 28/02/2019 21:20, Christian Borntraeger wrote: > > > On 22.02.2019 16:29, Pierre Morel wrote: >> We register the AP PQAP instruction hook during the open >> of the mediated device. And unregister it on release. >> >> In the AP PQAP instruction hook, if we receive a demand to >> enable IRQs, >> - we retrieve the vfio_ap_queue based on the APQN we receive >> in REG1, >> - we retrieve the page of the guest address, (NIB), from >> register REG2 >> - we the mediated device to use the VFIO pinning infratrsucture >> to pin the page of the guest address, >> - we retrieve the pointer to KVM to register the guest ISC >> and retrieve the host ISC >> - finaly we activate GISA >> >> If we receive a demand to disable IRQs, >> - we deactivate GISA >> - unregister from the GIB >> - unping the NIB >> >> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >> --- >> arch/s390/include/asm/kvm_host.h | 1 + >> drivers/s390/crypto/ap_bus.h | 1 + >> drivers/s390/crypto/vfio_ap_ops.c | 199 +++++++++++++++++++++++++++++++++- >> drivers/s390/crypto/vfio_ap_private.h | 1 + >> 4 files changed, 199 insertions(+), 3 deletions(-) >> >> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h >> index 49cc8b0..5f3bb8c 100644 >> --- a/arch/s390/include/asm/kvm_host.h >> +++ b/arch/s390/include/asm/kvm_host.h >> @@ -720,6 +720,7 @@ struct kvm_s390_cpu_model { >> struct kvm_s390_crypto { >> struct kvm_s390_crypto_cb *crycb; >> int (*pqap_hook)(struct kvm_vcpu *vcpu); >> + void *vfio_private; >> __u32 crycbd; >> __u8 aes_kw; >> __u8 dea_kw; >> diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h >> index bfc66e4..323f2aa 100644 >> --- a/drivers/s390/crypto/ap_bus.h >> +++ b/drivers/s390/crypto/ap_bus.h >> @@ -43,6 +43,7 @@ static inline int ap_test_bit(unsigned int *ptr, unsigned int nr) >> #define AP_RESPONSE_BUSY 0x05 >> #define AP_RESPONSE_INVALID_ADDRESS 0x06 >> #define AP_RESPONSE_OTHERWISE_CHANGED 0x07 >> +#define AP_RESPONSE_INVALID_GISA 0x08 >> #define AP_RESPONSE_Q_FULL 0x10 >> #define AP_RESPONSE_NO_PENDING_REPLY 0x10 >> #define AP_RESPONSE_INDEX_TOO_BIG 0x11 >> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c >> index 1b5130a..0196065 100644 >> --- a/drivers/s390/crypto/vfio_ap_ops.c >> +++ b/drivers/s390/crypto/vfio_ap_ops.c >> @@ -43,7 +43,7 @@ struct vfio_ap_queue *vfio_ap_get_queue(int apqn, struct list_head *l) >> return NULL; >> } >> >> -static int vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q) >> +int vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q) >> { >> struct ap_queue_status status; >> int retry = 20; >> @@ -75,6 +75,27 @@ static int vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q) >> return -EBUSY; >> } >> >> +/** >> + * vfio_ap_free_irq: >> + * @q: The vfio_ap_queue >> + * >> + * Unpin the guest NIB >> + * Unregister the ISC from the GIB alert >> + * Clear the vfio_ap_queue intern fields >> + */ >> +static void vfio_ap_free_irq(struct vfio_ap_queue *q) >> +{ >> + if (!q) >> + return; >> + if (q->g_pfn) >> + vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev), &q->g_pfn, 1); >> + if (q->isc) >> + kvm_s390_gisc_unregister(q->matrix_mdev->kvm, q->isc); >> + q->nib = 0; >> + q->isc = 0; >> + q->g_pfn = 0; >> +} > > Pierre, unless there is some magic, I think we need to free the gisa stuff before kvm exit. > > Imagine a malicious userspace that setups everything fine, but then closes all kvm file > descriptors but not the vfio file descriptor. This might result in random access to the > memory that contained the gisa potentially resulting in random memory overwrites. > > the problem is that kvm_destroy_vm calls kvm_arch_destroy_vm(kvm) before it calls > kvm_destroy_devices(kvm); So we already free the gisa before we do the unregister call. > > What about calling kvm_get_kvm/put from some of the callbacks in the right places. > > Debugging random memory overwrites is a PITA, so we either should document why I cannot > happen (even with malicious userspace) or simply fix the refcounting. >
OK, understood. I think we can do something simple by using kvm_get/kvm_put, as you suggested, in the vfio KVM notifier to ensure the order of the calls and also unregister the GISA at this moment. I will investigate in this direction.
Thanks Pierre
-- Pierre Morel Linux/KVM/QEMU in Böblingen - Germany
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