Re: [PATCH v3 40/49] hw/i386/sev: Add function to get SEV metadata from OVMF header

[Isaku Yamahata]

On Wed, Mar 20, 2024 at 03:39:36AM -0500,
Michael Roth <michael.roth@amd.com> wrote:

> From: Brijesh Singh <brijesh.singh@amd.com>
> 
> A recent version of OVMF expanded the reset vector GUID list to add
> SEV-specific metadata GUID. The SEV metadata describes the reserved
> memory regions such as the secrets and CPUID page used during the SEV-SNP
> guest launch.
> 
> The pc_system_get_ovmf_sev_metadata_ptr() is used to retieve the SEV
> metadata pointer from the OVMF GUID list.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
>  hw/i386/pc_sysfw_ovmf.c | 33 +++++++++++++++++++++++++++++++++
>  include/hw/i386/pc.h    | 26 ++++++++++++++++++++++++++
>  2 files changed, 59 insertions(+)
> 
> diff --git a/hw/i386/pc_sysfw_ovmf.c b/hw/i386/pc_sysfw_ovmf.c
> index 07a4c267fa..32efa34614 100644
> --- a/hw/i386/pc_sysfw_ovmf.c
> +++ b/hw/i386/pc_sysfw_ovmf.c
> @@ -35,6 +35,31 @@ static const int bytes_after_table_footer = 32;
>  static bool ovmf_flash_parsed;
>  static uint8_t *ovmf_table;
>  static int ovmf_table_len;
> +static OvmfSevMetadata *ovmf_sev_metadata_table;
> +
> +#define OVMF_SEV_META_DATA_GUID "dc886566-984a-4798-A75e-5585a7bf67cc"
> +typedef struct __attribute__((__packed__)) OvmfSevMetadataOffset {
> +    uint32_t offset;
> +} OvmfSevMetadataOffset;
> +
> +static void pc_system_parse_sev_metadata(uint8_t *flash_ptr, size_t 
> flash_size)
> +{
> +    OvmfSevMetadata     *metadata;
> +    OvmfSevMetadataOffset  *data;
> +
> +    if (!pc_system_ovmf_table_find(OVMF_SEV_META_DATA_GUID, (uint8_t 
> **)&data,
> +                                   NULL)) {
> +        return;
> +    }
> +
> +    metadata = (OvmfSevMetadata *)(flash_ptr + flash_size - data->offset);
> +    if (memcmp(metadata->signature, "ASEV", 4) != 0) {
> +        return;
> +    }
> +
> +    ovmf_sev_metadata_table = g_malloc(metadata->len);
> +    memcpy(ovmf_sev_metadata_table, metadata, metadata->len);
> +}
>  
>  void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, size_t flash_size)
>  {
> @@ -90,6 +115,9 @@ void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, size_t 
> flash_size)
>       */
>      memcpy(ovmf_table, ptr - tot_len, tot_len);
>      ovmf_table += tot_len;
> +
> +    /* Copy the SEV metadata table (if exist) */
> +    pc_system_parse_sev_metadata(flash_ptr, flash_size);
>  }

Can we move this call to x86_firmware_configure() @ pc_sysfw.c, and move sev
specific bits to somewhere to sev specific file?  We don't have to parse sev
metadata for non-SEV case, right?

We don't have to touch common ovmf file. It also will be consistent with tdx
case.  TDX patch series adds tdx_parse_tdvf() to x86_firmware_configure().

thanks,

>  
>  /**
> @@ -159,3 +187,8 @@ bool pc_system_ovmf_table_find(const char *entry, uint8_t 
> **data,
>      }
>      return false;
>  }
> +
> +OvmfSevMetadata *pc_system_get_ovmf_sev_metadata_ptr(void)
> +{
> +    return ovmf_sev_metadata_table;
> +}
> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> index fb1d4106e5..df9a61540d 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -163,6 +163,32 @@ void pc_acpi_smi_interrupt(void *opaque, int irq, int 
> level);
>  #define PCI_HOST_ABOVE_4G_MEM_SIZE     "above-4g-mem-size"
>  #define PCI_HOST_PROP_SMM_RANGES       "smm-ranges"
>  
> +typedef enum {
> +    SEV_DESC_TYPE_UNDEF,
> +    /* The section contains the region that must be validated by the VMM. */
> +    SEV_DESC_TYPE_SNP_SEC_MEM,
> +    /* The section contains the SNP secrets page */
> +    SEV_DESC_TYPE_SNP_SECRETS,
> +    /* The section contains address that can be used as a CPUID page */
> +    SEV_DESC_TYPE_CPUID,
> +
> +} ovmf_sev_metadata_desc_type;
> +
> +typedef struct __attribute__((__packed__)) OvmfSevMetadataDesc {
> +    uint32_t base;
> +    uint32_t len;
> +    ovmf_sev_metadata_desc_type type;
> +} OvmfSevMetadataDesc;
> +
> +typedef struct __attribute__((__packed__)) OvmfSevMetadata {
> +    uint8_t signature[4];
> +    uint32_t len;
> +    uint32_t version;
> +    uint32_t num_desc;
> +    OvmfSevMetadataDesc descs[];
> +} OvmfSevMetadata;
> +
> +OvmfSevMetadata *pc_system_get_ovmf_sev_metadata_ptr(void);
>  
>  void pc_pci_as_mapping_init(MemoryRegion *system_memory,
>                              MemoryRegion *pci_address_space);
> -- 
> 2.25.1
> 
> 

-- 
Isaku Yamahata <isaku.yamahata@intel.com>