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    Subject[PATCH v12 33/46] x86/boot: Add a pointer to Confidential Computing blob in bootparams
    From: Michael Roth <>

    The previously defined Confidential Computing blob is provided to the
    kernel via a setup_data structure or EFI config table entry. Currently
    these are both checked for by boot/compressed kernel to access the
    CPUID table address within it for use with SEV-SNP CPUID enforcement.

    To also enable SEV-SNP CPUID enforcement for the run-time kernel,
    similar early access to the CPUID table is needed early on while it's
    still using the identity-mapped page table set up by boot/compressed,
    where global pointers need to be accessed via fixup_pointer().

    This isn't much of an issue for accessing setup_data, and the EFI
    config table helper code currently used in boot/compressed *could* be
    used in this case as well since they both rely on identity-mapping.
    However, it has some reliance on EFI helpers/string constants that
    would need to be accessed via fixup_pointer(), and fixing it up while
    making it shareable between boot/compressed and run-time kernel is
    fragile and introduces a good bit of uglyness.

    Instead, add a boot_params->cc_blob_address pointer that the
    boot/compressed kernel can initialize so that the run-time kernel can
    access the CC blob from there instead of re-scanning the EFI config

    Also document these in Documentation/x86/zero-page.rst. While there,
    add missing documentation for the acpi_rsdp_addr field, which serves a
    similar purpose in providing the run-time kernel a pointer to the ACPI
    RSDP table so that it does not need to [re-]scan the EFI configuration

    Signed-off-by: Michael Roth <>
    Signed-off-by: Brijesh Singh <>
    Documentation/x86/zero-page.rst | 2 ++
    arch/x86/include/asm/bootparam_utils.h | 1 +
    arch/x86/include/uapi/asm/bootparam.h | 3 ++-
    3 files changed, 5 insertions(+), 1 deletion(-)

    diff --git a/Documentation/x86/zero-page.rst b/Documentation/x86/zero-page.rst
    index f088f5881666..45aa9cceb4f1 100644
    --- a/Documentation/x86/zero-page.rst
    +++ b/Documentation/x86/zero-page.rst
    @@ -19,6 +19,7 @@ Offset/Size Proto Name Meaning
    058/008 ALL tboot_addr Physical address of tboot shared page
    060/010 ALL ist_info Intel SpeedStep (IST) BIOS support information
    (struct ist_info)
    +070/008 ALL acpi_rsdp_addr Physical address of ACPI RSDP table
    080/010 ALL hd0_info hd0 disk parameter, OBSOLETE!!
    090/010 ALL hd1_info hd1 disk parameter, OBSOLETE!!
    0A0/010 ALL sys_desc_table System description table (struct sys_desc_table),
    @@ -27,6 +28,7 @@ Offset/Size Proto Name Meaning
    0C0/004 ALL ext_ramdisk_image ramdisk_image high 32bits
    0C4/004 ALL ext_ramdisk_size ramdisk_size high 32bits
    0C8/004 ALL ext_cmd_line_ptr cmd_line_ptr high 32bits
    +13C/004 ALL cc_blob_address Physical address of Confidential Computing blob
    140/080 ALL edid_info Video mode setup (struct edid_info)
    1C0/020 ALL efi_info EFI 32 information (struct efi_info)
    1E0/004 ALL alt_mem_k Alternative mem check, in KB
    diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h
    index 981fe923a59f..53e9b0620d96 100644
    --- a/arch/x86/include/asm/bootparam_utils.h
    +++ b/arch/x86/include/asm/bootparam_utils.h
    @@ -74,6 +74,7 @@ static void sanitize_boot_params(struct boot_params *boot_params)
    + BOOT_PARAM_PRESERVE(cc_blob_address),

    memset(&scratch, 0, sizeof(scratch));
    diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
    index 1ac5acca72ce..bea5cdcdf532 100644
    --- a/arch/x86/include/uapi/asm/bootparam.h
    +++ b/arch/x86/include/uapi/asm/bootparam.h
    @@ -188,7 +188,8 @@ struct boot_params {
    __u32 ext_ramdisk_image; /* 0x0c0 */
    __u32 ext_ramdisk_size; /* 0x0c4 */
    __u32 ext_cmd_line_ptr; /* 0x0c8 */
    - __u8 _pad4[116]; /* 0x0cc */
    + __u8 _pad4[112]; /* 0x0cc */
    + __u32 cc_blob_address; /* 0x13c */
    struct edid_info edid_info; /* 0x140 */
    struct efi_info efi_info; /* 0x1c0 */
    __u32 alt_mem_k; /* 0x1e0 */
     \ /
      Last update: 2022-03-07 22:39    [W:7.317 / U:0.024 seconds]
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