Re: [PATCH v3 01/11] KVM: SVM: Add KVM_SEV SEND_START command

[Singh, Brijesh]

On 8/22/19 5:08 AM, Borislav Petkov wrote:
> On Wed, Jul 10, 2019 at 08:13:00PM +0000, Singh, Brijesh wrote:
>> The command is used to create an outgoing SEV guest encryption context.
>>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
>> Cc: Joerg Roedel <joro@xxxxxxxxxx>
>> Cc: Borislav Petkov <bp@xxxxxxx>
>> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
>> Cc: x86@xxxxxxxxxx
>> Cc: kvm@xxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
>> ---
>>   .../virtual/kvm/amd-memory-encryption.rst     |  27 +++++
>>   arch/x86/kvm/svm.c                            | 105 ++++++++++++++++++
>>   include/uapi/linux/kvm.h                      |  12 ++
>>   3 files changed, 144 insertions(+)
>>
>> diff --git a/Documentation/virtual/kvm/amd-memory-encryption.rst b/Documentation/virtual/kvm/amd-memory-encryption.rst
>> index d18c97b4e140..0e9e1e9f9687 100644
>> --- a/Documentation/virtual/kvm/amd-memory-encryption.rst
>> +++ b/Documentation/virtual/kvm/amd-memory-encryption.rst
> 
> Do a
> 
> s/virtual/virt/g
> 
> for the next revision because this path got changed recently:
> 
> 2f5947dfcaec ("Documentation: move Documentation/virtual to Documentation/virt")
> 
>> @@ -238,6 +238,33 @@ Returns: 0 on success, -negative on error
>>                   __u32 trans_len;
>>           };
>>   
>> +10. KVM_SEV_SEND_START
>> +----------------------
>> +
>> +The KVM_SEV_SEND_START command can be used by the hypervisor to create an
>> +outgoing guest encryption context.
>> +
>> +Parameters (in): struct kvm_sev_send_start
>> +
>> +Returns: 0 on success, -negative on error
>> +
>> +::
>> +        struct kvm_sev_send_start {
>> +                __u32 policy;                 /* guest policy */
>> +
>> +                __u64 pdh_cert_uaddr;         /* platform Diffie-Hellman certificate */
>> +                __u32 pdh_cert_len;
>> +
>> +                __u64 plat_cert_uaddr;        /* platform certificate chain */
>> +                __u32 plat_cert_len;
>> +
>> +                __u64 amd_cert_uaddr;         /* AMD certificate */
>> +                __u32 amd_cert_len;
>> +
>> +                __u64 session_uaddr;         /* Guest session information */
>> +                __u32 session_len;
>> +        };
> 
> SEV API doc has "CERT" for PDH members but "CERTS" for the others.
> Judging by the description, you should do the same here too. Just so that
> there's no discrepancy from the docs.
> 

Noted.

>> +
>>   References
>>   ==========
>>   
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 48c865a4e5dd..0b0937f53520 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -6957,6 +6957,108 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
>>   	return ret;
>>   }
>>   
>> +static int sev_send_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
>> +{
>> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>> +	void *amd_cert = NULL, *session_data = NULL;
>> +	void *pdh_cert = NULL, *plat_cert = NULL;
>> +	struct sev_data_send_start *data = NULL;
> 
> Why are you initializing those to NULL?
> 

It simplifies the error handling path where we can do kfree() without
knowing whether the buffers were allocated or not.


> Also, SEV API text on SEND_START talks about a bunch of requirements in
> section
> 
> "6.8.1 Actions"
> 
> like
> 
> "The platform must be in the PSTATE.WORKING state.
> The guest must be in the GSTATE.RUNNING state.
> GCTX.POLICY.NOSEND must be zero. Otherwise, an error is returned.
> ..."
> 
> Where are we checking/verifying those?
> 


The kernel driver does not keep track of all those SEV VM states. The
userspace application (e.g qemu) will ensure that VM is in proper
state before calling those commands. If userspace does not check states
and makes a blind calls then we let the FW error out and propagate
the correct error message to the caller so that it can take the required
action.


>> +	struct kvm_sev_send_start params;
>> +	int ret;
>> +
>> +	if (!sev_guest(kvm))
>> +		return -ENOTTY;
>> +
>> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
>> +				sizeof(struct kvm_sev_send_start)))
>> +		return -EFAULT;
>> +
>> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
>> +	if (!data)
>> +		return -ENOMEM;
> 
> Move that allocation...
> 
>> +
>> +	/* userspace wants to query the session length */
>> +	if (!params.session_len)
>> +		goto cmd;
>> +
>> +	if (!params.pdh_cert_uaddr || !params.pdh_cert_len ||
>> +	    !params.session_uaddr)
>> +		return -EINVAL;
>> +
>> +	/* copy the certificate blobs from userspace */
>> +	pdh_cert = psp_copy_user_blob(params.pdh_cert_uaddr, params.pdh_cert_len);
>> +	if (IS_ERR(pdh_cert)) {
>> +		ret = PTR_ERR(pdh_cert);
>> +		goto e_free;
>> +	}
> 
> ... here so that it doesn't happen unnecessarily if the above fail.
> 

Noted.

>> +
>> +	data->pdh_cert_address = __psp_pa(pdh_cert);
>> +	data->pdh_cert_len = params.pdh_cert_len;
>> +
>> +	plat_cert = psp_copy_user_blob(params.plat_cert_uaddr, params.plat_cert_len);
>> +	if (IS_ERR(plat_cert)) {
>> +		ret = PTR_ERR(plat_cert);
>> +		goto e_free_pdh;
>> +	}
>> +
>> +	data->plat_cert_address = __psp_pa(plat_cert);
>> +	data->plat_cert_len = params.plat_cert_len;
>> +
>> +	amd_cert = psp_copy_user_blob(params.amd_cert_uaddr, params.amd_cert_len);
>> +	if (IS_ERR(amd_cert)) {
>> +		ret = PTR_ERR(amd_cert);
>> +		goto e_free_plat_cert;
>> +	}
>> +
>> +	data->amd_cert_address = __psp_pa(amd_cert);
>> +	data->amd_cert_len = params.amd_cert_len;
>> +
>> +	ret = -EINVAL;
>> +	if (params.session_len > SEV_FW_BLOB_MAX_SIZE)
>> +		goto e_free_amd_cert;
> 
> That check could go up where the other params.session_len check is
> happening and you can save yourself the cert alloc+freeing.
> 

I will take a look.

>> +
>> +	ret = -ENOMEM;
>> +	session_data = kmalloc(params.session_len, GFP_KERNEL);
>> +	if (!session_data)
>> +		goto e_free_amd_cert;
> 
> Ditto.
> 
> ...
>