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Subject: Re: [PATCH v4 2/2] s390: virtio: PV needs VIRTIO I/O device
 protection
To:     Cornelia Huck <cohuck@redhat.com>
Cc:     linux-kernel@vger.kernel.org, pasic@linux.ibm.com,
        borntraeger@de.ibm.com, frankja@linux.ibm.com, mst@redhat.com,
        jasowang@redhat.com, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org,
        virtualization@lists.linux-foundation.org, thomas.lendacky@amd.com,
        david@gibson.dropbear.id.au, linuxram@us.ibm.com,
        heiko.carstens@de.ibm.com, gor@linux.ibm.com
References: <1594111477-15401-1-git-send-email-pmorel@linux.ibm.com>
 <1594111477-15401-3-git-send-email-pmorel@linux.ibm.com>
 <20200707114633.68122a00.cohuck@redhat.com>
From:   Pierre Morel <pmorel@linux.ibm.com>
Message-ID: <e9976a77-f4a6-841d-6b95-59811751bce9@linux.ibm.com>
Date:   Tue, 7 Jul 2020 12:38:17 +0200
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On 2020-07-07 11:46, Cornelia Huck wrote:
> On Tue,  7 Jul 2020 10:44:37 +0200
> Pierre Morel <pmorel@linux.ibm.com> wrote:
> 
>> S390, protecting the guest memory against unauthorized host access
>> needs to enforce VIRTIO I/O device protection through the use of
>> VIRTIO_F_VERSION_1 and VIRTIO_F_IOMMU_PLATFORM.
> 
> Hm... what about:
> 
> "If protected virtualization is active on s390, the virtio queues are
> not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
> negotiated. Use the new arch_validate_virtio_features() interface to
> enforce this."

Yes, thanks.


> 
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> ---
>>   arch/s390/kernel/uv.c | 25 +++++++++++++++++++++++++
>>   1 file changed, 25 insertions(+)
>>
>> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
>> index c296e5c8dbf9..106330f6eda1 100644
>> --- a/arch/s390/kernel/uv.c
>> +++ b/arch/s390/kernel/uv.c
>> @@ -14,6 +14,7 @@
>>   #include <linux/memblock.h>
>>   #include <linux/pagemap.h>
>>   #include <linux/swap.h>
>> +#include <linux/virtio_config.h>
>>   #include <asm/facility.h>
>>   #include <asm/sections.h>
>>   #include <asm/uv.h>
>> @@ -413,3 +414,27 @@ static int __init uv_info_init(void)
>>   }
>>   device_initcall(uv_info_init);
>>   #endif
>> +
>> +/*
>> + * arch_validate_virtio_iommu_platform
> 
> s/arch_validate_virtio_iommu_platform/arch_validate_virtio_features/
> 
>> + * @dev: the VIRTIO device being added
>> + *
>> + * Return value: returns -ENODEV if any features of the
>> + *               device breaks the protected virtualization
>> + *               0 otherwise.
> 
> I don't think you need to specify the contract here: that belongs to
> the definition in the virtio core. What about simply adding a sentence
> "Return an error if required features are missing on a guest running
> with protected virtualization." ?

OK, right.

> 
>> + */
>> +int arch_validate_virtio_features(struct virtio_device *dev)
>> +{
> 
> Maybe jump out immediately if the guest is not protected?
> 
>> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
>> +		dev_warn(&dev->dev, "device must provide VIRTIO_F_VERSION_1\n");
>> +		return is_prot_virt_guest() ? -ENODEV : 0;
>> +	}
>> +
>> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
>> +		dev_warn(&dev->dev,
>> +			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
>> +		return is_prot_virt_guest() ? -ENODEV : 0;
>> +	}
> 
> if (!is_prot_virt_guest())
> 	return 0;
> 
> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> 	dev_warn(&dev->dev,
>                   "legacy virtio is incompatible with protected guests");
> 	return -ENODEV;
> }
> 
> if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> 	dev_warn(&dev->dev,
> 		 "device does not work with limited memory access in protected guests");
> 	return -ENODEV;
> }

Yes, easier to read.

Thanks,
Pierre


-- 
Pierre Morel
IBM Lab Boeblingen