Re: [PATCH v4 18/31] hw/i386/sev: Add function to get SEV metadata from OVMF header

[Liam Merwick via <qemu-devel@nongnu.org>]

On 30/05/2024 12:16, Pankaj Gupta 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

typo: retieve


> 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>
> Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
> ---
>   hw/i386/pc_sysfw.c   |  4 ++++
>   include/hw/i386/pc.h | 26 ++++++++++++++++++++++++++
>   target/i386/sev.c    | 31 +++++++++++++++++++++++++++++++
>   target/i386/sev.h    |  2 ++
>   4 files changed, 63 insertions(+)
> 
> diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
> index ac88ad4eb9..048d0919c1 100644
> --- a/hw/i386/pc_sysfw.c
> +++ b/hw/i386/pc_sysfw.c
> @@ -260,6 +260,10 @@ void x86_firmware_configure(void *ptr, int size)
>       pc_system_parse_ovmf_flash(ptr, size);
>   
>       if (sev_enabled()) {
> +
> +        /* Copy the SEV metadata table (if exist) */

Maybe s/exist/it exists/


> +        pc_system_parse_sev_metadata(ptr, size);
> +
>           ret = sev_es_save_reset_vector(ptr, size);
>           if (ret) {
>               error_report("failed to locate and/or save reset vector");
> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> index ad9c3d9ba8..c653b8eeb2 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -164,6 +164,32 @@ 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);
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 2ca9a86bf3..d9d1d97f0c 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -611,6 +611,37 @@ SevCapability *qmp_query_sev_capabilities(Error **errp)
>       return sev_get_capabilities(errp);
>   }
>   
> +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;
> +
> +OvmfSevMetadata *pc_system_get_ovmf_sev_metadata_ptr(void)
> +{
> +    return ovmf_sev_metadata_table;
> +}
> +
> +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);

There should be a bounds check on metadata->len before using it.


> +    memcpy(ovmf_sev_metadata_table, metadata, metadata->len);
> +}
> +
>   static SevAttestationReport *sev_get_attestation_report(const char *mnonce,
>                                                           Error **errp)
>   {
> diff --git a/target/i386/sev.h b/target/i386/sev.h
> index 5dc4767b1e..cc12824dd6 100644
> --- a/target/i386/sev.h
> +++ b/target/i386/sev.h
> @@ -66,4 +66,6 @@ int sev_inject_launch_secret(const char *hdr, const char *secret,
>   int sev_es_save_reset_vector(void *flash_ptr, uint64_t flash_size);
>   void sev_es_set_reset_vector(CPUState *cpu);
>   
> +void pc_system_parse_sev_metadata(uint8_t *flash_ptr, size_t flash_size);
> +
>   #endif