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Thu, 02 Apr 2020 18:57:14 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 032IcI4c069907; Thu, 2 Apr 2020 18:57:14 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3020.oracle.com with ESMTP id 302ga2xm50-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 02 Apr 2020 18:57:13 +0000 Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 032IvBC4004851; Thu, 2 Apr 2020 18:57:11 GMT Received: from vbusired-dt (/10.154.166.66) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 02 Apr 2020 11:57:10 -0700 Date: Thu, 2 Apr 2020 13:57:06 -0500 From: Venu Busireddy To: Brijesh Singh Cc: Ashish Kalra , pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, joro@8bytes.org, bp@suse.de, thomas.lendacky@amd.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, rientjes@google.com, srutherford@google.com, luto@kernel.org Subject: Re: [PATCH v6 01/14] KVM: SVM: Add KVM_SEV SEND_START command Message-ID: <20200402185706.GA655878@vbusired-dt> References: <3f90333959fd49bed184d45a761cc338424bf614.1585548051.git.ashish.kalra@amd.com> <20200402062726.GA647295@vbusired-dt> <89a586e4-8074-0d32-f384-a4597975d129@amd.com> <20200402163717.GA653926@vbusired-dt> <8b1b4874-11a8-1422-5ea1-ed665f41ab5c@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8b1b4874-11a8-1422-5ea1-ed665f41ab5c@amd.com> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9579 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=5 malwarescore=0 mlxlogscore=999 bulkscore=0 mlxscore=0 spamscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004020141 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9579 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 lowpriorityscore=0 malwarescore=0 adultscore=0 priorityscore=1501 mlxlogscore=999 bulkscore=0 suspectscore=5 mlxscore=0 spamscore=0 impostorscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004020141 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-02 13:04:13 -0500, Brijesh Singh wrote: > > On 4/2/20 11:37 AM, Venu Busireddy wrote: > > On 2020-04-02 07:59:54 -0500, Brijesh Singh wrote: > >> Hi Venu, > >> > >> Thanks for the feedback. > >> > >> On 4/2/20 1:27 AM, Venu Busireddy wrote: > >>> On 2020-03-30 06:19:59 +0000, Ashish Kalra wrote: > >>>> From: Brijesh Singh > >>>> > >>>> The command is used to create an outgoing SEV guest encryption context. > >>>> > >>>> Cc: Thomas Gleixner > >>>> Cc: Ingo Molnar > >>>> Cc: "H. Peter Anvin" > >>>> Cc: Paolo Bonzini > >>>> Cc: "Radim Krčmář" > >>>> Cc: Joerg Roedel > >>>> Cc: Borislav Petkov > >>>> Cc: Tom Lendacky > >>>> Cc: x86@kernel.org > >>>> Cc: kvm@vger.kernel.org > >>>> Cc: linux-kernel@vger.kernel.org > >>>> Reviewed-by: Steve Rutherford > >>>> Signed-off-by: Brijesh Singh > >>>> Signed-off-by: Ashish Kalra > >>>> --- > >>>> .../virt/kvm/amd-memory-encryption.rst | 27 ++++ > >>>> arch/x86/kvm/svm.c | 128 ++++++++++++++++++ > >>>> include/linux/psp-sev.h | 8 +- > >>>> include/uapi/linux/kvm.h | 12 ++ > >>>> 4 files changed, 171 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 */ > >>> Could this please be changed to plat_certs_uaddr, as it is referred to > >>> in the rest of the code? > >>> > >>>> + __u32 plat_certs_len; > >>>> + > >>>> + __u64 amd_certs_uaddr; /* AMD certificate */ > >>>> + __u32 amd_cert_len; > >>> Could this please be changed to amd_certs_len, as it is referred to in > >>> the rest of the code? > >>> > >>>> + > >>>> + __u64 session_uaddr; /* Guest session information */ > >>>> + __u32 session_len; > >>>> + }; > >>>> + > >>>> References > >>>> ========== > >>>> > >>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > >>>> index 50d1ebafe0b3..63d172e974ad 100644 > >>>> --- a/arch/x86/kvm/svm.c > >>>> +++ b/arch/x86/kvm/svm.c > >>>> @@ -7149,6 +7149,131 @@ 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(¶ms, (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, > >>>> + ¶ms); > >>>> + > >>>> + /* 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; > >>>> + > >>>> + ret = sev_issue_cmd(kvm, SEV_CMD_SEND_START, data, &argp->error); > >>>> + > >>>> + if (ret) > >>>> + goto e_free; > >>>> + > >>>> + if (copy_to_user((void __user *)(uintptr_t) params.session_uaddr, > >>>> + session_data, params.session_len)) { > >>>> + ret = -EFAULT; > >>>> + goto e_free; > >>>> + } > >>> To optimize the amount of data being copied to user space, could the > >>> above section of code changed as follows? > >>> > >>> params.session_len = data->session_len; > >>> if (copy_to_user((void __user *)(uintptr_t) params.session_uaddr, > >>> session_data, params.session_len)) { > >>> ret = -EFAULT; > >>> goto e_free; > >>> } > >> > >> We should not be using the data->session_len, it will cause -EFAULT when > >> user has not allocated enough space in the session_uaddr. Lets consider > >> the case where user passes session_len=10 but firmware thinks the > >> session length should be 64. In that case the data->session_len will > >> contains a value of 64 but userspace has allocated space for 10 bytes > >> and copy_to_user() will fail. If we are really concern about the amount > >> of data getting copied to userspace then use min_t(size_t, > >> params.session_len, data->session_len). > > We are allocating a buffer of params.session_len size and passing that > > buffer, and that length via data->session_len, to the firmware. Why would > > the firmware set data->session_len to a larger value, in spite of telling > > it that the buffer is only params.session_len long? I thought that only > > the reverse is possible, that is, the user sets the params.session_len > > to the MAX, but the session data is actually smaller than that size. > > > The question is, how does a userspace know the session length ? One > method is you can precalculate a value based on your firmware version > and have userspace pass that, or another approach is set > params.session_len = 0 and query it from the FW. The FW spec allow to > query the length, please see the spec. In the qemu patches I choose > second approach. This is because session blob can change from one FW > version to another and I tried to avoid calculating or hardcoding the > length for a one version of the FW. You can certainly choose the first > method. We want to ensure that kernel interface works on the both cases. I like the fact that you have already implemented the functionality to facilitate the user space to obtain the session length from the firmware (by setting params.session_len to 0). However, I am trying to address the case where the user space sets the params.session_len to a size smaller than the size needed. Let me put it differently. Let us say that the session blob needs 128 bytes, but the user space sets params.session_len to 16. That results in us allocating a buffer of 16 bytes, and set data->session_len to 16. What does the firmware do now? Does it copy 128 bytes into data->session_address, or, does it copy 16 bytes? If it copies 128 bytes, we most certainly will end up with a kernel crash. If it copies 16 bytes, then what does it set in data->session_len? 16, or 128? If 16, everything is good. If 128, we end up causing memory access violation for the user space. Perhaps, this can be dealt a little differently? Why not always call sev_issue_cmd(kvm, SEV_CMD_SEND_START, ...) with zeroed out data? Then, if the user space has set params.session_len to 0, we return with the needed params.session_len. Otherwise, we check if params.session_len is large enough, and if not, we return -EINVAL? > > > > Also, if for whatever reason the firmware sets data->session_len to > > a larger value than what is passed, what is the user space expected > > to do when the call returns? If the user space tries to access > > params.session_len amount of data, it will possibly get a memory access > > violation, because it did not originally allocate that large a buffer. > > > > If we do go with using min_t(size_t, params.session_len, > > data->session_len), then params.session_len should also be set to the > > smaller of the two, right? > > > >>>> + > >>>> + params.policy = data->policy; > >>>> + params.session_len = data->session_len; > >>>> + if (copy_to_user((void __user *)(uintptr_t)argp->data, ¶ms, > >>>> + sizeof(struct kvm_sev_send_start))) > >>>> + ret = -EFAULT; > >>> Since the only fields that are changed in the kvm_sev_send_start structure > >>> are session_len and policy, why do we need to copy the entire structure > >>> back to the user? Why not just those two values? Please see the changes > >>> proposed to kvm_sev_send_start structure further below to accomplish this. > >> I think we also need to consider the code readability while saving the > >> CPU cycles. This is very small structure. By duplicating into two calls > >> #1 copy params.policy and #2 copy params.session_len we will add more > >> CPU cycle. And, If we get creative and rearrange the structure then code > >> readability is lost because now the copy will depend on how the > >> structure is layout in the memory. > > I was not recommending splitting that call into two. That would certainly > > be more expensive, than copying the entire structure. That is the reason > > why I suggested reordering the members of kvm_sev_send_start. Isn't > > there plenty of code where structures are defined in a way to keep the > > data movement efficient? :-) > > > > Please see my other comment below. > > > >>> params.policy = data->policy; > >>> if (copy_to_user((void __user *)(uintptr_t)argp->data, ¶ms, > >>> sizeof(params.policy) + sizeof(params.session_len)) > >>> 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; > >>>> +} > >>>> + > >>>> static int svm_mem_enc_op(struct kvm *kvm, void __user *argp) > >>>> { > >>>> struct kvm_sev_cmd sev_cmd; > >>>> @@ -7193,6 +7318,9 @@ static 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 4b95f9a31a2f..17bef4c245e1 100644 > >>>> --- a/include/uapi/linux/kvm.h > >>>> +++ b/include/uapi/linux/kvm.h > >>>> @@ -1558,6 +1558,18 @@ 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; > >>>> +}; > >>> Redo this structure as below: > >>> > >>> struct kvm_sev_send_start { > >>> __u32 policy; > >>> __u32 session_len; > >>> __u64 session_uaddr; > >>> __u64 pdh_cert_uaddr; > >>> __u32 pdh_cert_len; > >>> __u64 plat_certs_uaddr; > >>> __u32 plat_certs_len; > >>> __u64 amd_certs_uaddr; > >>> __u32 amd_certs_len; > >>> }; > >>> > >>> Or as below, just to make it look better. > >>> > >>> struct kvm_sev_send_start { > >>> __u32 policy; > >>> __u32 session_len; > >>> __u64 session_uaddr; > >>> __u32 pdh_cert_len; > >>> __u64 pdh_cert_uaddr; > >>> __u32 plat_certs_len; > >>> __u64 plat_certs_uaddr; > >>> __u32 amd_certs_len; > >>> __u64 amd_certs_uaddr; > >>> }; > >>> > >> Wherever applicable, I tried  best to not divert from the SEV spec > >> structure layout. Anyone who is reading the SEV FW spec  will see a > >> similar structure layout in the KVM/PSP header files. I would prefer to > >> stick to that approach. > > This structure is in uapi, and is anyway different from the > > sev_data_send_start, right? Does it really need to stay close to the > > firmware structure layout? Just because the firmware folks thought of > > a structure layout, that should not prevent our code to be efficient. > > > >> > >>>> + > >>>> #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 > >>>>