[RFC,v8,54/56] x86/sev: Add KVM commands for instance certs

Commit Message

Michael Roth Feb. 20, 2023, 6:38 p.m. UTC

From: Dionna Glaze <[e-mail]>

The /dev/sev device has the ability to store host-wide certificates for
the key used by the AMD-SP for SEV-SNP attestation report signing,
but for hosts that want to specify additional certificates that are
specific to the image launched in a VM, a different way is needed to
communicate those certificates.

Add two new KVM ioctl to handle this: KVM_SEV_SNP_{GET,SET}_CERTS

The certificates that are set with this command are expected to follow
the same format as the host certificates, but that format is opaque
to the kernel.

The new behavior for custom certificates is that the extended guest
request command will now return the overridden certificates if they
were installed for the instance. The error condition for a too small
data buffer is changed to return the overridden certificate data size
if there is an overridden certificate set installed.

Setting a 0 length certificate returns the system state to only return
the host certificates on an extended guest request.

Also increase the SEV_FW_BLOB_MAX_SIZE another 4K page to allow space
for an extra certificate.

Cc: Tom Lendacky <[e-mail]>
Cc: Paolo Bonzini <[e-mail]>

Signed-off-by: Dionna Glaze <[e-mail]>
Signed-off-by: Ashish Kalra <[e-mail]>
[mdr: remove used of "we" and "this patch" in commit log]
Signed-off-by: Michael Roth <[e-mail]>
---
 arch/x86/kvm/svm/sev.c   | 111 ++++++++++++++++++++++++++++++++++++++-
 arch/x86/kvm/svm/svm.h   |   1 +
 include/linux/psp-sev.h  |   2 +-
 include/uapi/linux/kvm.h |  12 +++++
 4 files changed, 123 insertions(+), 3 deletions(-)

Comments

Dov Murik Feb. 21, 2023, 12:40 p.m. UTC | #1

Hi Mike,

On 20/02/2023 20:38, Michael Roth wrote:
> From: Dionna Glaze <[e-mail]>
> 
> The /dev/sev device has the ability to store host-wide certificates for
> the key used by the AMD-SP for SEV-SNP attestation report signing,
> but for hosts that want to specify additional certificates that are
> specific to the image launched in a VM, a different way is needed to
> communicate those certificates.
> 
> Add two new KVM ioctl to handle this: KVM_SEV_SNP_{GET,SET}_CERTS
> 
> The certificates that are set with this command are expected to follow
> the same format as the host certificates, but that format is opaque
> to the kernel.
> 
> The new behavior for custom certificates is that the extended guest
> request command will now return the overridden certificates if they
> were installed for the instance. The error condition for a too small
> data buffer is changed to return the overridden certificate data size
> if there is an overridden certificate set installed.
> 
> Setting a 0 length certificate returns the system state to only return
> the host certificates on an extended guest request.
> 
> Also increase the SEV_FW_BLOB_MAX_SIZE another 4K page to allow space
> for an extra certificate.
> 
> Cc: Tom Lendacky <[e-mail]>
> Cc: Paolo Bonzini <[e-mail]>
> 
> Signed-off-by: Dionna Glaze <[e-mail]>
> Signed-off-by: Ashish Kalra <[e-mail]>
> [mdr: remove used of "we" and "this patch" in commit log]
> Signed-off-by: Michael Roth <[e-mail]>
> ---
>  arch/x86/kvm/svm/sev.c   | 111 ++++++++++++++++++++++++++++++++++++++-
>  arch/x86/kvm/svm/svm.h   |   1 +
>  include/linux/psp-sev.h  |   2 +-
>  include/uapi/linux/kvm.h |  12 +++++
>  4 files changed, 123 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 70d5650d8d95..18b64b7005e7 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2089,6 +2089,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		goto e_free;
>  
>  	sev->snp_certs_data = certs_data;
> +	sev->snp_certs_len = 0;
>  
>  	return context;
>  
> @@ -2404,6 +2405,86 @@ static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	return ret;
>  }
>  
> +static int snp_get_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	struct kvm_sev_snp_get_certs params;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (!sev->snp_context)
> +		return -EINVAL;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	/* No instance certs set. */
> +	if (!sev->snp_certs_len)
> +		return -ENOENT;
> +
> +	if (params.certs_len < sev->snp_certs_len) {
> +		/* Output buffer too small. Return the required size. */
> +		params.certs_len = sev->snp_certs_len;
> +
> +		if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
> +				 sizeof(params)))
> +			return -EFAULT;
> +
> +		return -EINVAL;
> +	}
> +
> +	if (copy_to_user((void __user *)(uintptr_t)params.certs_uaddr,
> +			 sev->snp_certs_data, sev->snp_certs_len))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +static int snp_set_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	unsigned long length = SEV_FW_BLOB_MAX_SIZE;
> +	void *to_certs = sev->snp_certs_data;
> +	struct kvm_sev_snp_set_certs params;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (!sev->snp_context)
> +		return -EINVAL;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	if (params.certs_len > SEV_FW_BLOB_MAX_SIZE)
> +		return -EINVAL;
> +
> +	/*
> +	 * Setting a length of 0 is the same as "uninstalling" instance-
> +	 * specific certificates.
> +	 */
> +	if (params.certs_len == 0) {
> +		sev->snp_certs_len = 0;
> +		return 0;
> +	}
> +
> +	/* Page-align the length */
> +	length = (params.certs_len + PAGE_SIZE - 1) & PAGE_MASK;
> +

In comments on v7 [1] Dionna agreed adding cleanup here:

  /* The size could shrink and leave garbage at the end. */
  memset(sev->snp_certs_data, 0, SEV_FW_BLOB_MAX_SIZE);

(we can use 'to_certs' in the first argument)

but it wasn't added in v8.

-Dov

[1] https://lore.kernel.org/linux-coco/CAAH4kHYOtzgqSTZQFcRiZwPLCkLAThjsCMdjUCdsBTiP=[e-mail]/


> +	if (copy_from_user(to_certs,
> +			   (void __user *)(uintptr_t)params.certs_uaddr,
> +			   params.certs_len)) {
> +		return -EFAULT;
> +	}
> +
> +	sev->snp_certs_len = length;
> +
> +	return 0;
> +}
> +
>  int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>  {
>  	struct kvm_sev_cmd sev_cmd;
> @@ -2503,6 +2584,12 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>  	case KVM_SEV_SNP_LAUNCH_FINISH:
>  		r = snp_launch_finish(kvm, &sev_cmd);
>  		break;
> +	case KVM_SEV_SNP_GET_CERTS:
> +		r = snp_get_instance_certs(kvm, &sev_cmd);
> +		break;
> +	case KVM_SEV_SNP_SET_CERTS:
> +		r = snp_set_instance_certs(kvm, &sev_cmd);
> +		break;
>  	default:
>  		r = -EINVAL;
>  		goto out;
> @@ -3550,8 +3637,28 @@ static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gp
>  	if (rc)
>  		goto unlock;
>  
> -	rc = snp_guest_ext_guest_request(&req, (unsigned long)sev->snp_certs_data,
> -					 &data_npages, &err);
> +	/*
> +	 * If the VMM has overridden the certs, then change the error message
> +	 * if the size is inappropriate for the override. Otherwise, use a
> +	 * regular guest request and copy back the instance certs.
> +	 */
> +	if (sev->snp_certs_len) {
> +		if ((data_npages << PAGE_SHIFT) < sev->snp_certs_len) {
> +			rc = -EINVAL;
> +			err = SNP_GUEST_REQ_INVALID_LEN;
> +			goto datalen;
> +		}
> +		rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &req,
> +				   (int *)&err);
> +	} else {
> +		rc = snp_guest_ext_guest_request(&req,
> +						 (unsigned long)sev->snp_certs_data,
> +						 &data_npages, &err);
> +	}
> +datalen:
> +	if (sev->snp_certs_len)
> +		data_npages = sev->snp_certs_len >> PAGE_SHIFT;
> +
>  	if (rc) {
>  		/*
>  		 * If buffer length is small then return the expected
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 221b38d3c845..dced46559508 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -94,6 +94,7 @@ struct kvm_sev_info {
>  	u64 snp_init_flags;
>  	void *snp_context;      /* SNP guest context page */
>  	void *snp_certs_data;
> +	unsigned int snp_certs_len; /* Size of instance override for certs */
>  	struct mutex guest_req_lock; /* Lock for guest request handling */
>  
>  	u64 sev_features;	/* Features set at VMSA creation */
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 92116e2b74fd..3b28b78938f6 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -22,7 +22,7 @@
>  #define __psp_pa(x)	__pa(x)
>  #endif
>  
> -#define SEV_FW_BLOB_MAX_SIZE	0x4000	/* 16KB */
> +#define SEV_FW_BLOB_MAX_SIZE	0x5000	/* 20KB */
>  
>  /**
>   * SEV platform state
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 6e684bf5f723..ad7e24e43547 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1928,6 +1928,8 @@ enum sev_cmd_id {
>  	KVM_SEV_SNP_LAUNCH_START,
>  	KVM_SEV_SNP_LAUNCH_UPDATE,
>  	KVM_SEV_SNP_LAUNCH_FINISH,
> +	KVM_SEV_SNP_GET_CERTS,
> +	KVM_SEV_SNP_SET_CERTS,
>  
>  	KVM_SEV_NR_MAX,
>  };
> @@ -2075,6 +2077,16 @@ struct kvm_sev_snp_launch_finish {
>  	__u8 pad[6];
>  };
>  
> +struct kvm_sev_snp_get_certs {
> +	__u64 certs_uaddr;
> +	__u64 certs_len;
> +};
> +
> +struct kvm_sev_snp_set_certs {
> +	__u64 certs_uaddr;
> +	__u64 certs_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)

Zhi Wang March 2, 2023, 12:02 a.m. UTC | #2

On Mon, 20 Feb 2023 12:38:45 -0600
Michael Roth <[e-mail]> wrote:

In the host-wide certificates installing/uninstalling, a lock is to
prevent the racing between cert upload/download path and the handling
of guest request path.

Guess we need a similar lock to prevent the racing between
snp_{set,get}_instance_certs() and snp_handle_ext_guest_request().

This patch and PATCH 27 are focusing on cert from different sources.
It would be better to abstract. With the functions and data structure
of cert, the cert installing/uninstalling, checks, expectation of the
output buffer can be unified. Then we don't need mostly duplicate
routines in two different paths.

> From: Dionna Glaze <[e-mail]>
> 
> The /dev/sev device has the ability to store host-wide certificates for
> the key used by the AMD-SP for SEV-SNP attestation report signing,
> but for hosts that want to specify additional certificates that are
> specific to the image launched in a VM, a different way is needed to
> communicate those certificates.
> 
> Add two new KVM ioctl to handle this: KVM_SEV_SNP_{GET,SET}_CERTS
> 
> The certificates that are set with this command are expected to follow
> the same format as the host certificates, but that format is opaque
> to the kernel.
> 
> The new behavior for custom certificates is that the extended guest
> request command will now return the overridden certificates if they
> were installed for the instance. The error condition for a too small
> data buffer is changed to return the overridden certificate data size
> if there is an overridden certificate set installed.
> 
> Setting a 0 length certificate returns the system state to only return
> the host certificates on an extended guest request.
> 
> Also increase the SEV_FW_BLOB_MAX_SIZE another 4K page to allow space
> for an extra certificate.
> 
> Cc: Tom Lendacky <[e-mail]>
> Cc: Paolo Bonzini <[e-mail]>
> 
> Signed-off-by: Dionna Glaze <[e-mail]>
> Signed-off-by: Ashish Kalra <[e-mail]>
> [mdr: remove used of "we" and "this patch" in commit log]
> Signed-off-by: Michael Roth <[e-mail]>
> ---
>  arch/x86/kvm/svm/sev.c   | 111 ++++++++++++++++++++++++++++++++++++++-
>  arch/x86/kvm/svm/svm.h   |   1 +
>  include/linux/psp-sev.h  |   2 +-
>  include/uapi/linux/kvm.h |  12 +++++
>  4 files changed, 123 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 70d5650d8d95..18b64b7005e7 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -2089,6 +2089,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  		goto e_free;
>  
>  	sev->snp_certs_data = certs_data;
> +	sev->snp_certs_len = 0;
>  
>  	return context;
>  

Better to move the fix to PATCH 45.

> @@ -2404,6 +2405,86 @@ static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  	return ret;
>  }
>  
> +static int snp_get_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	struct kvm_sev_snp_get_certs params;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (!sev->snp_context)
> +		return -EINVAL;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	/* No instance certs set. */
> +	if (!sev->snp_certs_len)
> +		return -ENOENT;
> +
> +	if (params.certs_len < sev->snp_certs_len) {
> +		/* Output buffer too small. Return the required size. */
> +		params.certs_len = sev->snp_certs_len;
> +
> +		if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
> +				 sizeof(params)))
> +			return -EFAULT;
> +
> +		return -EINVAL;
> +	}
> +
> +	if (copy_to_user((void __user *)(uintptr_t)params.certs_uaddr,
> +			 sev->snp_certs_data, sev->snp_certs_len))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +static int snp_set_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	unsigned long length = SEV_FW_BLOB_MAX_SIZE;
> +	void *to_certs = sev->snp_certs_data;
> +	struct kvm_sev_snp_set_certs params;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (!sev->snp_context)
> +		return -EINVAL;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	if (params.certs_len > SEV_FW_BLOB_MAX_SIZE)
> +		return -EINVAL;
> +
> +	/*
> +	 * Setting a length of 0 is the same as "uninstalling" instance-
> +	 * specific certificates.
> +	 */
> +	if (params.certs_len == 0) {
> +		sev->snp_certs_len = 0;
> +		return 0;
> +	}
> +
> +	/* Page-align the length */
> +	length = (params.certs_len + PAGE_SIZE - 1) & PAGE_MASK;
> +
> +	if (copy_from_user(to_certs,
> +			   (void __user *)(uintptr_t)params.certs_uaddr,
> +			   params.certs_len)) {
> +		return -EFAULT;
> +	}
> +
> +	sev->snp_certs_len = length;
> +
> +	return 0;
> +}
> +
>  int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>  {
>  	struct kvm_sev_cmd sev_cmd;
> @@ -2503,6 +2584,12 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
>  	case KVM_SEV_SNP_LAUNCH_FINISH:
>  		r = snp_launch_finish(kvm, &sev_cmd);
>  		break;
> +	case KVM_SEV_SNP_GET_CERTS:
> +		r = snp_get_instance_certs(kvm, &sev_cmd);
> +		break;
> +	case KVM_SEV_SNP_SET_CERTS:
> +		r = snp_set_instance_certs(kvm, &sev_cmd);
> +		break;
>  	default:
>  		r = -EINVAL;
>  		goto out;
> @@ -3550,8 +3637,28 @@ static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gp
>  	if (rc)
>  		goto unlock;
>  
> -	rc = snp_guest_ext_guest_request(&req, (unsigned long)sev->snp_certs_data,
> -					 &data_npages, &err);
> +	/*
> +	 * If the VMM has overridden the certs, then change the error message
> +	 * if the size is inappropriate for the override. Otherwise, use a
> +	 * regular guest request and copy back the instance certs.
> +	 */
> +	if (sev->snp_certs_len) {
> +		if ((data_npages << PAGE_SHIFT) < sev->snp_certs_len) {
> +			rc = -EINVAL;
> +			err = SNP_GUEST_REQ_INVALID_LEN;
> +			goto datalen;
> +		}
> +		rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &req,
> +				   (int *)&err);
> +	} else {
> +		rc = snp_guest_ext_guest_request(&req,
> +						 (unsigned long)sev->snp_certs_data,
> +						 &data_npages, &err);
> +	}
> +datalen:
> +	if (sev->snp_certs_len)
> +		data_npages = sev->snp_certs_len >> PAGE_SHIFT;
> +
>  	if (rc) {
>  		/*
>  		 * If buffer length is small then return the expected
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 221b38d3c845..dced46559508 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -94,6 +94,7 @@ struct kvm_sev_info {
>  	u64 snp_init_flags;
>  	void *snp_context;      /* SNP guest context page */
>  	void *snp_certs_data;
> +	unsigned int snp_certs_len; /* Size of instance override for certs */
>  	struct mutex guest_req_lock; /* Lock for guest request handling */
>  
>  	u64 sev_features;	/* Features set at VMSA creation */
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 92116e2b74fd..3b28b78938f6 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -22,7 +22,7 @@
>  #define __psp_pa(x)	__pa(x)
>  #endif
>  
> -#define SEV_FW_BLOB_MAX_SIZE	0x4000	/* 16KB */
> +#define SEV_FW_BLOB_MAX_SIZE	0x5000	/* 20KB */
>  
>  /**
>   * SEV platform state
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 6e684bf5f723..ad7e24e43547 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1928,6 +1928,8 @@ enum sev_cmd_id {
>  	KVM_SEV_SNP_LAUNCH_START,
>  	KVM_SEV_SNP_LAUNCH_UPDATE,
>  	KVM_SEV_SNP_LAUNCH_FINISH,
> +	KVM_SEV_SNP_GET_CERTS,
> +	KVM_SEV_SNP_SET_CERTS,
>  
>  	KVM_SEV_NR_MAX,
>  };
> @@ -2075,6 +2077,16 @@ struct kvm_sev_snp_launch_finish {
>  	__u8 pad[6];
>  };
>  
> +struct kvm_sev_snp_get_certs {
> +	__u64 certs_uaddr;
> +	__u64 certs_len;
> +};
> +
> +struct kvm_sev_snp_set_certs {
> +	__u64 certs_uaddr;
> +	__u64 certs_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)

Dionna Amalie Glaze March 2, 2023, 1:41 a.m. UTC | #3

> > @@ -2089,6 +2089,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
> >               goto e_free;
> >
> >       sev->snp_certs_data = certs_data;
> > +     sev->snp_certs_len = 0;
> >
> >       return context;
> >
>
> Better to move the fix to PATCH 45.
>

This part isn't a fix, but part of the implementation since
snp_certs_len is added in this patch here

> > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> > index 221b38d3c845..dced46559508 100644
> > --- a/arch/x86/kvm/svm/svm.h
> > +++ b/arch/x86/kvm/svm/svm.h
> > @@ -94,6 +94,7 @@ struct kvm_sev_info {
> >       u64 snp_init_flags;
> >       void *snp_context;      /* SNP guest context page */
> >       void *snp_certs_data;
> > +     unsigned int snp_certs_len; /* Size of instance override for certs */
> >       struct mutex guest_req_lock; /* Lock for guest request handling */
> >
> >       u64 sev_features;       /* Features set at VMSA creation */

Zhi Wang March 2, 2023, 11:27 a.m. UTC | #4

On Wed, 1 Mar 2023 17:41:11 -0800
Dionna Amalie Glaze <[e-mail]> wrote:

> > > @@ -2089,6 +2089,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > >               goto e_free;
> > >
> > >       sev->snp_certs_data = certs_data;
> > > +     sev->snp_certs_len = 0;
> > >
> > >       return context;
> > >
> >
> > Better to move the fix to PATCH 45.
> >
> 
> This part isn't a fix, but part of the implementation since
> snp_certs_len is added in this patch here
>

I see. My bad. Was thinking it was the snp_serts_len in the global sev as
they has the same name.
 
> > > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> > > index 221b38d3c845..dced46559508 100644
> > > --- a/arch/x86/kvm/svm/svm.h
> > > +++ b/arch/x86/kvm/svm/svm.h
> > > @@ -94,6 +94,7 @@ struct kvm_sev_info {
> > >       u64 snp_init_flags;
> > >       void *snp_context;      /* SNP guest context page */
> > >       void *snp_certs_data;
> > > +     unsigned int snp_certs_len; /* Size of instance override for certs */
> > >       struct mutex guest_req_lock; /* Lock for guest request handling */
> > >
> > >       u64 sev_features;       /* Features set at VMSA creation */
> 
>

Dov Murik March 2, 2023, 11:34 a.m. UTC | #5

On 20/02/2023 20:38, Michael Roth wrote:
> From: Dionna Glaze <[e-mail]>
> 
> The /dev/sev device has the ability to store host-wide certificates for
> the key used by the AMD-SP for SEV-SNP attestation report signing,
> but for hosts that want to specify additional certificates that are
> specific to the image launched in a VM, a different way is needed to
> communicate those certificates.
> 
> Add two new KVM ioctl to handle this: KVM_SEV_SNP_{GET,SET}_CERTS
> 
> The certificates that are set with this command are expected to follow
> the same format as the host certificates, but that format is opaque
> to the kernel.
> 
> The new behavior for custom certificates is that the extended guest
> request command will now return the overridden certificates if they
> were installed for the instance. The error condition for a too small
> data buffer is changed to return the overridden certificate data size
> if there is an overridden certificate set installed.
> 
> Setting a 0 length certificate returns the system state to only return
> the host certificates on an extended guest request.
> 
> Also increase the SEV_FW_BLOB_MAX_SIZE another 4K page to allow space
> for an extra certificate.
> 
> Cc: Tom Lendacky <[e-mail]>
> Cc: Paolo Bonzini <[e-mail]>
> 
> Signed-off-by: Dionna Glaze <[e-mail]>
> Signed-off-by: Ashish Kalra <[e-mail]>
> [mdr: remove used of "we" and "this patch" in commit log]
> Signed-off-by: Michael Roth <[e-mail]>
> ---
>  arch/x86/kvm/svm/sev.c   | 111 ++++++++++++++++++++++++++++++++++++++-
>  arch/x86/kvm/svm/svm.h   |   1 +
>  include/linux/psp-sev.h  |   2 +-
>  include/uapi/linux/kvm.h |  12 +++++
>  4 files changed, 123 insertions(+), 3 deletions(-)
> 

[...]

> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 92116e2b74fd..3b28b78938f6 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -22,7 +22,7 @@
>  #define __psp_pa(x)	__pa(x)
>  #endif
>  
> -#define SEV_FW_BLOB_MAX_SIZE	0x4000	/* 16KB */
> +#define SEV_FW_BLOB_MAX_SIZE	0x5000	/* 20KB */

This change should be removed (it was also discussed in v7).  If I
understand correctly, 16KB is a limit of the PSP.

-Dov


>  
>  /**
>   * SEV platform state

Patch

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 70d5650d8d95..18b64b7005e7 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2089,6 +2089,7 @@  static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
 		goto e_free;
 
 	sev->snp_certs_data = certs_data;
+	sev->snp_certs_len = 0;
 
 	return context;
 
@@ -2404,6 +2405,86 @@  static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
+static int snp_get_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct kvm_sev_snp_get_certs params;
+
+	if (!sev_snp_guest(kvm))
+		return -ENOTTY;
+
+	if (!sev->snp_context)
+		return -EINVAL;
+
+	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
+			   sizeof(params)))
+		return -EFAULT;
+
+	/* No instance certs set. */
+	if (!sev->snp_certs_len)
+		return -ENOENT;
+
+	if (params.certs_len < sev->snp_certs_len) {
+		/* Output buffer too small. Return the required size. */
+		params.certs_len = sev->snp_certs_len;
+
+		if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
+				 sizeof(params)))
+			return -EFAULT;
+
+		return -EINVAL;
+	}
+
+	if (copy_to_user((void __user *)(uintptr_t)params.certs_uaddr,
+			 sev->snp_certs_data, sev->snp_certs_len))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int snp_set_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	unsigned long length = SEV_FW_BLOB_MAX_SIZE;
+	void *to_certs = sev->snp_certs_data;
+	struct kvm_sev_snp_set_certs params;
+
+	if (!sev_snp_guest(kvm))
+		return -ENOTTY;
+
+	if (!sev->snp_context)
+		return -EINVAL;
+
+	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
+			   sizeof(params)))
+		return -EFAULT;
+
+	if (params.certs_len > SEV_FW_BLOB_MAX_SIZE)
+		return -EINVAL;
+
+	/*
+	 * Setting a length of 0 is the same as "uninstalling" instance-
+	 * specific certificates.
+	 */
+	if (params.certs_len == 0) {
+		sev->snp_certs_len = 0;
+		return 0;
+	}
+
+	/* Page-align the length */
+	length = (params.certs_len + PAGE_SIZE - 1) & PAGE_MASK;
+
+	if (copy_from_user(to_certs,
+			   (void __user *)(uintptr_t)params.certs_uaddr,
+			   params.certs_len)) {
+		return -EFAULT;
+	}
+
+	sev->snp_certs_len = length;
+
+	return 0;
+}
+
 int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_sev_cmd sev_cmd;
@@ -2503,6 +2584,12 @@  int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
 	case KVM_SEV_SNP_LAUNCH_FINISH:
 		r = snp_launch_finish(kvm, &sev_cmd);
 		break;
+	case KVM_SEV_SNP_GET_CERTS:
+		r = snp_get_instance_certs(kvm, &sev_cmd);
+		break;
+	case KVM_SEV_SNP_SET_CERTS:
+		r = snp_set_instance_certs(kvm, &sev_cmd);
+		break;
 	default:
 		r = -EINVAL;
 		goto out;
@@ -3550,8 +3637,28 @@  static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gp
 	if (rc)
 		goto unlock;
 
-	rc = snp_guest_ext_guest_request(&req, (unsigned long)sev->snp_certs_data,
-					 &data_npages, &err);
+	/*
+	 * If the VMM has overridden the certs, then change the error message
+	 * if the size is inappropriate for the override. Otherwise, use a
+	 * regular guest request and copy back the instance certs.
+	 */
+	if (sev->snp_certs_len) {
+		if ((data_npages << PAGE_SHIFT) < sev->snp_certs_len) {
+			rc = -EINVAL;
+			err = SNP_GUEST_REQ_INVALID_LEN;
+			goto datalen;
+		}
+		rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &req,
+				   (int *)&err);
+	} else {
+		rc = snp_guest_ext_guest_request(&req,
+						 (unsigned long)sev->snp_certs_data,
+						 &data_npages, &err);
+	}
+datalen:
+	if (sev->snp_certs_len)
+		data_npages = sev->snp_certs_len >> PAGE_SHIFT;
+
 	if (rc) {
 		/*
 		 * If buffer length is small then return the expected
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 221b38d3c845..dced46559508 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -94,6 +94,7 @@  struct kvm_sev_info {
 	u64 snp_init_flags;
 	void *snp_context;      /* SNP guest context page */
 	void *snp_certs_data;
+	unsigned int snp_certs_len; /* Size of instance override for certs */
 	struct mutex guest_req_lock; /* Lock for guest request handling */
 
 	u64 sev_features;	/* Features set at VMSA creation */
diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
index 92116e2b74fd..3b28b78938f6 100644
--- a/include/linux/psp-sev.h
+++ b/include/linux/psp-sev.h
@@ -22,7 +22,7 @@ 
 #define __psp_pa(x)	__pa(x)
 #endif
 
-#define SEV_FW_BLOB_MAX_SIZE	0x4000	/* 16KB */
+#define SEV_FW_BLOB_MAX_SIZE	0x5000	/* 20KB */
 
 /**
  * SEV platform state
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 6e684bf5f723..ad7e24e43547 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1928,6 +1928,8 @@  enum sev_cmd_id {
 	KVM_SEV_SNP_LAUNCH_START,
 	KVM_SEV_SNP_LAUNCH_UPDATE,
 	KVM_SEV_SNP_LAUNCH_FINISH,
+	KVM_SEV_SNP_GET_CERTS,
+	KVM_SEV_SNP_SET_CERTS,
 
 	KVM_SEV_NR_MAX,
 };
@@ -2075,6 +2077,16 @@  struct kvm_sev_snp_launch_finish {
 	__u8 pad[6];
 };
 
+struct kvm_sev_snp_get_certs {
+	__u64 certs_uaddr;
+	__u64 certs_len;
+};
+
+struct kvm_sev_snp_set_certs {
+	__u64 certs_uaddr;
+	__u64 certs_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)