Re: [PATCH v7 01/18] KVM: SVM: Add KVM_SEV SEND_START command

[Ashish Kalra <ashish.kalra@amd.com>]

On Mon, May 04, 2020 at 06:10:50PM -0500, Venu Busireddy wrote:
> On 2020-05-04 22:36:37 +0000, Ashish Kalra wrote:
> > On Mon, May 04, 2020 at 04:07:17PM -0500, Venu Busireddy wrote:
> > > On 2020-04-30 08:40:34 +0000, Ashish Kalra wrote:
> > > > From: Brijesh Singh <Brijesh.Singh@amd.com>
> > > > 
> > > > The command is used to create an outgoing SEV guest encryption context.
> > > > 
> > > > Cc: Thomas Gleixner <tglx@linutronix.de>
> > > > Cc: Ingo Molnar <mingo@redhat.com>
> > > > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > > > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > > > Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> > > > Cc: Joerg Roedel <joro@8bytes.org>
> > > > Cc: Borislav Petkov <bp@suse.de>
> > > > Cc: Tom Lendacky <thomas.lendacky@amd.com>
> > > > Cc: x86@kernel.org
> > > > Cc: kvm@vger.kernel.org
> > > > Cc: linux-kernel@vger.kernel.org
> > > > Reviewed-by: Steve Rutherford <srutherford@google.com>
> > > > Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>
> > > > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> > > > Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> > > > ---
> > > >  .../virt/kvm/amd-memory-encryption.rst        |  27 ++++
> > > >  arch/x86/kvm/svm/sev.c                        | 125 ++++++++++++++++++
> > > >  include/linux/psp-sev.h                       |   8 +-
> > > >  include/uapi/linux/kvm.h                      |  12 ++
> > > >  4 files changed, 168 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst
> > > > index c3129b9ba5cb..4fd34fc5c7a7 100644
> > > > --- a/Documentation/virt/kvm/amd-memory-encryption.rst
> > > > +++ b/Documentation/virt/kvm/amd-memory-encryption.rst
> > > > @@ -263,6 +263,33 @@ 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_certs_uadr;        /* platform certificate chain */
> > > 
> > > Can this be changed as mentioned in the previous review
> > > (https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fkvm%2F20200402062726.GA647295%40vbusired-dt%2F&amp;data=02%7C01%7Cashish.kalra%40amd.com%7Cf8d037dd37224ed4a33608d7f08067f5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637242306610788233&amp;sdata=eu1SgC6ukawOuxTeAoA3mzKiMNWlPCCa5lGEVs9D1s0%3D&amp;reserved=0)?
> > > 
> > > > +                __u32 plat_certs_len;
> > > > +
> > > > +                __u64 amd_certs_uaddr;        /* AMD certificate */
> > > > +                __u32 amd_cert_len;
> > > 
> > > Can this be changed as mentioned in the previous review
> > > (https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fkvm%2F20200402062726.GA647295%40vbusired-dt%2F&amp;data=02%7C01%7Cashish.kalra%40amd.com%7Cf8d037dd37224ed4a33608d7f08067f5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637242306610798235&amp;sdata=7xgp4ko8VGokGGQz1X1yPhz1ZXY9R501YginoDcen90%3D&amp;reserved=0)?
> > > 
> > > > +
> > > > +                __u64 session_uaddr;          /* Guest session information */
> > > > +                __u32 session_len;
> > > > +        };
> > > > +
> > > >  References
> > > >  ==========
> > > >  
> > > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > > > index cf912b4aaba8..5a15b43b4349 100644
> > > > --- a/arch/x86/kvm/svm/sev.c
> > > > +++ b/arch/x86/kvm/svm/sev.c
> > > > @@ -913,6 +913,128 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > > >  	return ret;
> > > >  }
> > > >  
> > > > +/* Userspace wants to query session length. */
> > > > +static int
> > > > +__sev_send_start_query_session_length(struct kvm *kvm, struct kvm_sev_cmd *argp,
> > > > +				      struct kvm_sev_send_start *params)
> > > > +{
> > > > +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > > > +	struct sev_data_send_start *data;
> > > > +	int ret;
> > > > +
> > > > +	data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
> > > > +	if (data == NULL)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	data->handle = sev->handle;
> > > > +	ret = sev_issue_cmd(kvm, SEV_CMD_SEND_START, data, &argp->error);
> > > > +
> > > > +	params->session_len = data->session_len;
> > > > +	if (copy_to_user((void __user *)(uintptr_t)argp->data, params,
> > > > +				sizeof(struct kvm_sev_send_start)))
> > > > +		ret = -EFAULT;
> > > > +
> > > > +	kfree(data);
> > > > +	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;
> > > > +	struct sev_data_send_start *data;
> > > > +	struct kvm_sev_send_start params;
> > > > +	void *amd_certs, *session_data;
> > > > +	void *pdh_cert, *plat_certs;
> > > > +	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;
> > > > +
> > > > +	/* if session_len is zero, userspace wants to query the session length */
> > > > +	if (!params.session_len)
> > > > +		return __sev_send_start_query_session_length(kvm, argp,
> > > > +				&params);
> > > > +
> > > > +	/* some sanity checks */
> > > > +	if (!params.pdh_cert_uaddr || !params.pdh_cert_len ||
> > > > +	    !params.session_uaddr || params.session_len > SEV_FW_BLOB_MAX_SIZE)
> > > > +		return -EINVAL;
> > > > +
> > > > +	/* allocate the memory to hold the session data blob */
> > > > +	session_data = kmalloc(params.session_len, GFP_KERNEL_ACCOUNT);
> > > > +	if (!session_data)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	/* 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_session;
> > > > +	}
> > > > +
> > > > +	plat_certs = psp_copy_user_blob(params.plat_certs_uaddr,
> > > > +				params.plat_certs_len);
> > > > +	if (IS_ERR(plat_certs)) {
> > > > +		ret = PTR_ERR(plat_certs);
> > > > +		goto e_free_pdh;
> > > > +	}
> > > > +
> > > > +	amd_certs = psp_copy_user_blob(params.amd_certs_uaddr,
> > > > +				params.amd_certs_len);
> > > > +	if (IS_ERR(amd_certs)) {
> > > > +		ret = PTR_ERR(amd_certs);
> > > > +		goto e_free_plat_cert;
> > > > +	}
> > > > +
> > > > +	data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
> > > > +	if (data == NULL) {
> > > > +		ret = -ENOMEM;
> > > > +		goto e_free_amd_cert;
> > > > +	}
> > > > +
> > > > +	/* populate the FW SEND_START field with system physical address */
> > > > +	data->pdh_cert_address = __psp_pa(pdh_cert);
> > > > +	data->pdh_cert_len = params.pdh_cert_len;
> > > > +	data->plat_certs_address = __psp_pa(plat_certs);
> > > > +	data->plat_certs_len = params.plat_certs_len;
> > > > +	data->amd_certs_address = __psp_pa(amd_certs);
> > > > +	data->amd_certs_len = params.amd_certs_len;
> > > > +	data->session_address = __psp_pa(session_data);
> > > > +	data->session_len = params.session_len;
> > > > +	data->handle = sev->handle;
> > > > +
> > > 
> > > Can the following code be changed as acknowledged in
> > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fkvm%2Ff715bf99-0158-4d5f-77f3-b27743db3c59%40amd.com%2F&amp;data=02%7C01%7Cashish.kalra%40amd.com%7Cf8d037dd37224ed4a33608d7f08067f5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637242306610798235&amp;sdata=s3ZwfpCm94x2LCNN8I1jjcWcrkj3Nrw5PnOvxdDxSCs%3D&amp;reserved=0?
> > > 
> > 
> > I believe that this has been already addressed as discussed :
> > 
> > Ah, so the main issue is we should not be going to e_free on error. If
> > session_len is less than the expected len then FW will return an error.
> > In the case of an error we can skip copying the session_data into
> > userspace buffer but we still need to pass the session_len and policy
> > back to the userspace.
> > 
> > So this patch is still returning session_len and policy back to user
> > in case of error : ( as the code below shows )
> > 
> > if (!ret && copy_to_user((void
> > __user*)(uintptr_t)params.session_uaddr,...
> 
> This fix addresses only one part of the problem. I am referring to the
> other suggestion about avoiding copying the entire kvm_sev_send_start
> structure back to the user. As I was mentioning in the discussion,
> the only fields that changed are the policy and session_len fields. So,
> why copy back the entire structure? Why not just those two fields?
> 
> > 

Both policy and session_len are two different fields in the
kvm_sev_send_start structure, why to complicate it by using two
different copy_to_user()'s here, to send two 32-bit words back to user,
it's much simpler to copy the whole structure back in one copy_to_user() 
(makes it less complicated with no additional address computations),
also this is just a session start code, so it is invoked once at
the beginning of the migration process and it is not a performance
critical path such that saving few bytes of copy_to_user() wil affect it.

Thanks,
Ashish

> > 
> > > > +	ret = sev_issue_cmd(kvm, SEV_CMD_SEND_START, data, &argp->error);
> > > > +
> > > > +	if (!ret && copy_to_user((void __user *)(uintptr_t)params.session_uaddr,
> > > > +			session_data, params.session_len)) {
> > > > +		ret = -EFAULT;
> > > > +		goto e_free;
> > > > +	}
> > > > +
> > > > +	params.policy = data->policy;
> > > > +	params.session_len = data->session_len;
> > > > +	if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
> > > > +				sizeof(struct kvm_sev_send_start)))
> > > > +		ret = -EFAULT;
> > > > +
> > > > +e_free:
> > > > +	kfree(data);
> > > > +e_free_amd_cert:
> > > > +	kfree(amd_certs);
> > > > +e_free_plat_cert:
> > > > +	kfree(plat_certs);
> > > > +e_free_pdh:
> > > > +	kfree(pdh_cert);
> > > > +e_free_session:
> > > > +	kfree(session_data);
> > > > +	return ret;
> > > > +}
> > > > +
> > > >  int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> > > >  {
> > > >  	struct kvm_sev_cmd sev_cmd;
> > > > @@ -957,6 +1079,9 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> > > >  	case KVM_SEV_LAUNCH_SECRET:
> > > >  		r = sev_launch_secret(kvm, &sev_cmd);
> > > >  		break;
> > > > +	case KVM_SEV_SEND_START:
> > > > +		r = sev_send_start(kvm, &sev_cmd);
> > > > +		break;
> > > >  	default:
> > > >  		r = -EINVAL;
> > > >  		goto out;
> > > > diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> > > > index 5167bf2bfc75..9f63b9d48b63 100644
> > > > --- a/include/linux/psp-sev.h
> > > > +++ b/include/linux/psp-sev.h
> > > > @@ -323,11 +323,11 @@ struct sev_data_send_start {
> > > >  	u64 pdh_cert_address;			/* In */
> > > >  	u32 pdh_cert_len;			/* In */
> > > >  	u32 reserved1;
> > > > -	u64 plat_cert_address;			/* In */
> > > > -	u32 plat_cert_len;			/* In */
> > > > +	u64 plat_certs_address;			/* In */
> > > > +	u32 plat_certs_len;			/* In */
> > > >  	u32 reserved2;
> > > > -	u64 amd_cert_address;			/* In */
> > > > -	u32 amd_cert_len;			/* In */
> > > > +	u64 amd_certs_address;			/* In */
> > > > +	u32 amd_certs_len;			/* In */
> > > >  	u32 reserved3;
> > > >  	u64 session_address;			/* In */
> > > >  	u32 session_len;			/* In/Out */
> > > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > > > index 428c7dde6b4b..8827d43e2684 100644
> > > > --- a/include/uapi/linux/kvm.h
> > > > +++ b/include/uapi/linux/kvm.h
> > > > @@ -1598,6 +1598,18 @@ struct kvm_sev_dbg {
> > > >  	__u32 len;
> > > >  };
> > > >  
> > > > +struct kvm_sev_send_start {
> > > > +	__u32 policy;
> > > > +	__u64 pdh_cert_uaddr;
> > > > +	__u32 pdh_cert_len;
> > > > +	__u64 plat_certs_uaddr;
> > > > +	__u32 plat_certs_len;
> > > > +	__u64 amd_certs_uaddr;
> > > > +	__u32 amd_certs_len;
> > > > +	__u64 session_uaddr;
> > > > +	__u32 session_len;
> > > > +};
> > > > +
> > > >  #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
> > > >  #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
> > > >  #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)
> > > > -- 
> > > > 2.17.1
> > > >