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

[Dov Murik]

On 20/02/2023 20:38, Michael Roth wrote:
> From: Dionna Glaze <dionnaglaze@xxxxxxxxxx>
> 
> 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 <Thomas.Lendacky@xxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> 
> Signed-off-by: Dionna Glaze <dionnaglaze@xxxxxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> [mdr: remove used of "we" and "this patch" in commit log]
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
>  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