linux-kernel - Re: [RFC Part2 PATCH v3 19/26] KVM: svm: Add support for SEV GUEST

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Date:   Thu, 14 Sep 2017 06:25:17 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...e.de>
Cc:     brijesh.singh@....com, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        \"Radim Krčmář\" <rkrcmar@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFC Part2 PATCH v3 19/26] KVM: svm: Add support for SEV
 GUEST_STATUS command

On 9/14/17 5:35 AM, Borislav Petkov wrote:
...

> +
>> +	if (copy_from_user(&params, (void *) argp->data,
>> +				sizeof(struct kvm_sev_guest_status)))
> Let me try to understand what's going on here. You copy user data into
> params...

This is wrong -- since all the parameters in GET_STATUS is "OUT" hence
we don't need to perform copy_from_user. I will fix it. thanks

>
>> +		return -EFAULT;
>> +
>> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
>> +	if (!data)
>> +		return -ENOMEM;
>> +
>> +	data->handle = sev_get_handle(kvm);
>> +	ret = sev_issue_cmd(kvm, SEV_CMD_GUEST_STATUS, data, &argp->error);
>> +	if (ret)
>> +		goto e_free;
>> +
>> +	params.policy = data->policy;
>> +	params.state = data->state;
>> +	params.handle = data->handle;
> ... *overwrite* the copied data which means, the copy meant *absolutely*
> *nothing* at all! ...
>
> Also, why does userspace need to know the firmware ->handle?

SEV firmware supports key-sharing, if guest policy allows sharing the
key between VMs then we need the firmware->handle. If key-sharing
feature is used then firmware->handle of the 1st VM will be passed into
the LAUNCH_START of  2nd VM.  I still have not coded up anything in qemu
for key-sharing and also I am using GET_STATUS command in qemu yet. But
wanted to make sure that if we decide to add "info sev-status" command
in qemu-monitor to retrieve the SEV state information and then all the
information is available to us.