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This useful when updating the reported TCB or signing key with commands such as SNP_SET_CONFIG/SNP_COMMIT/SNP_VLEK_LOAD, since they may in turn require updates to userspace-supplied certificates, and if an attestation request happens to be in-flight at the time those updates are occurring there is potential for a guest to receive a certificate blob that is out of sync with the effective signing key for the attestation report. These interfaces also provide some versatility with how similar firmware/certificate update activities can be handled in the future. Reviewed-by: Tom Lendacky Signed-off-by: Michael Roth --- Documentation/virt/coco/sev-guest.rst | 50 +++++++++++++++++++++++++-- arch/x86/include/asm/sev.h | 6 ++++ arch/x86/virt/svm/sev.c | 43 +++++++++++++++++++++++ drivers/crypto/ccp/sev-dev.c | 47 +++++++++++++++++++++++++ include/uapi/linux/psp-sev.h | 12 +++++++ 5 files changed, 156 insertions(+), 2 deletions(-) diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst index de68d3a4b540..ab192a008ba7 100644 --- a/Documentation/virt/coco/sev-guest.rst +++ b/Documentation/virt/coco/sev-guest.rst @@ -128,8 +128,6 @@ the SEV-SNP specification for further details. The SNP_GET_EXT_REPORT ioctl is similar to the SNP_GET_REPORT. The difference is related to the additional certificate data that is returned with the report. -The certificate data returned is being provided by the hypervisor through the -SNP_SET_EXT_CONFIG. The ioctl uses the SNP_GUEST_REQUEST (MSG_REPORT_REQ) command provided by the SEV-SNP firmware to get the attestation report. @@ -195,6 +193,54 @@ them into the system after obtaining them from the KDS, and corresponds closely to the SNP_VLEK_LOAD firmware command specified in the SEV-SNP spec. +2.8 SNP_PAUSE_ATTESTATION / SNP_RESUME_ATTESTATION +-------------------------------------------------- +:Technology: sev-snp +:Type: hypervisor ioctl cmd +:Parameters (out): struct sev_user_data_snp_pause_transaction +:Returns (out): 0 on success, -negative on error + +When requesting attestation reports, SNP guests have the option of issuing +an extended guest request which allows host userspace to supply additional +certificate data that can be used to validate the signature used to sign +the attestation report. This signature is generated using a key that is +derived from the reported TCB that can be set via the SNP_SET_CONFIG and +SNP_COMMIT ioctls, so the accompanying certificate data needs to be kept in +sync with the changes made to the reported TCB via these ioctls. + +Similarly, interfaces like SNP_LOAD_VLEK can modify the key used to sign +the attestation reports, which may in turn require updating the certificate +data provided to guests via extended guest requests. + +To allow for updating the reported TCB, endorsement key, and any certificate +data in a manner that is atomic to guests, the SNP_PAUSE_ATTESTATION and +SNP_RESUME_ATTESTATION commands are provided. + +After SNP_PAUSE_ATTESTATION is issued, any attestation report requests via +extended guest requests that are in-progress, or received after +SNP_PAUSE_ATTESTATION is issued, will result in the guest receiving a +GHCB-defined error message instructing it to retry the request. Once all +the desired reported TCB, endorsement keys, or certificate data updates +are completed on the host, the SNP_RESUME_ATTESTATION command must be +issued to allow guest attestation requests to proceed. + +In general, hosts should serialize updates of this sort and never have more +than 1 outstanding transaction in flight that could result in the +interleaving of multiple SNP_PAUSE_ATTESTATION/SNP_RESUME_ATTESTATION pairs. +To guard against this, SNP_PAUSE_ATTESTATION will fail if another process +has already paused attestation requests. + +However, there may be occassions where a transaction needs to be aborted due +to unexpected activity in userspace such as timeouts, crashes, etc., so +SNP_RESUME_ATTESTATION will always succeed. Nonetheless, this could +potentially lead to SNP_RESUME_ATTESTATION being called out of sequence, so +to allow for callers of SNP_{PAUSE,RESUME}_ATTESTATION to detect such +occurrences, each ioctl will return a transaction ID in the response so the +caller can monitor whether the start/end ID both match. If they don't, the +caller should assume that attestation has been paused/resumed unexpectedly, +and take whatever measures it deems necessary such as logging, reporting, +auditing the sequence of events. + 3. SEV-SNP CPUID Enforcement ============================ diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h index 3a06f06b847a..ee24ef815e35 100644 --- a/arch/x86/include/asm/sev.h +++ b/arch/x86/include/asm/sev.h @@ -82,6 +82,8 @@ extern void vc_no_ghcb(void); extern void vc_boot_ghcb(void); extern bool handle_vc_boot_ghcb(struct pt_regs *regs); +extern struct mutex snp_pause_attestation_lock; + /* PVALIDATE return codes */ #define PVALIDATE_FAIL_SIZEMISMATCH 6 @@ -272,6 +274,8 @@ int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, u32 asid, bool immut int rmp_make_shared(u64 pfn, enum pg_level level); void snp_leak_pages(u64 pfn, unsigned int npages); void kdump_sev_callback(void); +int snp_pause_attestation(u64 *transaction_id); +void snp_resume_attestation(u64 *transaction_id); #else static inline bool snp_probe_rmptable_info(void) { return false; } static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return -ENODEV; } @@ -285,6 +289,8 @@ static inline int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, u32 as static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV; } static inline void snp_leak_pages(u64 pfn, unsigned int npages) {} static inline void kdump_sev_callback(void) { } +static inline int snp_pause_attestation(u64 *transaction_id) { return 0; } +static inline void snp_resume_attestation(u64 *transaction_id) {} #endif #endif diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c index ab0e8448bb6e..b75f2e7d4012 100644 --- a/arch/x86/virt/svm/sev.c +++ b/arch/x86/virt/svm/sev.c @@ -70,6 +70,11 @@ static DEFINE_SPINLOCK(snp_leaked_pages_list_lock); static unsigned long snp_nr_leaked_pages; +/* For synchronizing TCB/certificate updates with extended guest requests */ +DEFINE_MUTEX(snp_pause_attestation_lock); +static u64 snp_transaction_id; +static bool snp_attestation_paused; + #undef pr_fmt #define pr_fmt(fmt) "SEV-SNP: " fmt @@ -568,3 +573,41 @@ void kdump_sev_callback(void) if (cc_platform_has(CC_ATTR_HOST_SEV_SNP)) wbinvd(); } + +int snp_pause_attestation(u64 *transaction_id) +{ + mutex_lock(&snp_pause_attestation_lock); + + if (snp_attestation_paused) { + mutex_unlock(&snp_pause_attestation_lock); + return -EBUSY; + } + + /* + * The actual transaction ID update will happen when + * snp_resume_attestation() is called, so return + * the *anticipated* transaction ID that will be + * returned by snp_resume_attestation(). This is + * to ensure that unbalanced/aborted transactions will + * be noticeable when the caller that started the + * transaction calls snp_resume_attestation(). + */ + *transaction_id = snp_transaction_id + 1; + snp_attestation_paused = true; + + mutex_unlock(&snp_pause_attestation_lock); + + return 0; +} +EXPORT_SYMBOL_GPL(snp_pause_attestation); + +void snp_resume_attestation(u64 *transaction_id) +{ + mutex_lock(&snp_pause_attestation_lock); + + snp_attestation_paused = false; + *transaction_id = ++snp_transaction_id; + + mutex_unlock(&snp_pause_attestation_lock); +} +EXPORT_SYMBOL_GPL(snp_resume_attestation); diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c index 97a7959406ee..7eb18a273731 100644 --- a/drivers/crypto/ccp/sev-dev.c +++ b/drivers/crypto/ccp/sev-dev.c @@ -2060,6 +2060,47 @@ static int sev_ioctl_do_snp_vlek_load(struct sev_issue_cmd *argp, bool writable) return ret; } +static int sev_ioctl_do_snp_pause_attestation(struct sev_issue_cmd *argp, bool writable) +{ + struct sev_user_data_snp_pause_attestation transaction = {0}; + struct sev_device *sev = psp_master->sev_data; + int ret; + + if (!sev->snp_initialized || !argp->data) + return -EINVAL; + + if (!writable) + return -EPERM; + + ret = snp_pause_attestation(&transaction.id); + if (ret) + return ret; + + if (copy_to_user((void __user *)argp->data, &transaction, sizeof(transaction))) + return -EFAULT; + + return 0; +} + +static int sev_ioctl_do_snp_resume_attestation(struct sev_issue_cmd *argp, bool writable) +{ + struct sev_user_data_snp_pause_attestation transaction = {0}; + struct sev_device *sev = psp_master->sev_data; + + if (!sev->snp_initialized || !argp->data) + return -EINVAL; + + if (!writable) + return -EPERM; + + snp_resume_attestation(&transaction.id); + + if (copy_to_user((void __user *)argp->data, &transaction, sizeof(transaction))) + return -EFAULT; + + return 0; +} + static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg) { void __user *argp = (void __user *)arg; @@ -2123,6 +2164,12 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg) case SNP_VLEK_LOAD: ret = sev_ioctl_do_snp_vlek_load(&input, writable); break; + case SNP_PAUSE_ATTESTATION: + ret = sev_ioctl_do_snp_pause_attestation(&input, writable); + break; + case SNP_RESUME_ATTESTATION: + ret = sev_ioctl_do_snp_resume_attestation(&input, writable); + break; default: ret = -EINVAL; goto out; diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h index 2289b7c76c59..7b35b2814a99 100644 --- a/include/uapi/linux/psp-sev.h +++ b/include/uapi/linux/psp-sev.h @@ -32,6 +32,8 @@ enum { SNP_COMMIT, SNP_SET_CONFIG, SNP_VLEK_LOAD, + SNP_PAUSE_ATTESTATION, + SNP_RESUME_ATTESTATION, SEV_MAX, }; @@ -241,6 +243,16 @@ struct sev_user_data_snp_wrapped_vlek_hashstick { __u8 data[432]; /* In */ } __packed; +/** + * struct sev_user_data_snp_pause_attestation - metadata for pausing attestation + * + * @id: the ID of the transaction started/ended by a call to SNP_PAUSE_ATTESTATION + * or SNP_RESUME_ATTESTATION, respectively. + */ +struct sev_user_data_snp_pause_attestation { + __u64 id; /* Out */ +} __packed; + /** * struct sev_issue_cmd - SEV ioctl parameters *