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    Subject[PATCH Part1 RFC v4 27/36] x86/boot: add a pointer to Confidential Computing blob in bootparams
    Date
    From: Michael Roth <michael.roth@amd.com>

    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 is 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, this patch adds a boot_params->cc_blob_address pointer that
    boot/compressed can initialize so that the run-time kernel can access
    the prelocated CC blob that way instead.

    Signed-off-by: Michael Roth <michael.roth@amd.com>
    Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    ---
    arch/x86/include/asm/bootparam_utils.h | 1 +
    arch/x86/include/uapi/asm/bootparam.h | 3 ++-
    2 files changed, 3 insertions(+), 1 deletion(-)

    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(hdr),
    BOOT_PARAM_PRESERVE(e820_table),
    BOOT_PARAM_PRESERVE(eddbuf),
    + 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 */
    --
    2.17.1
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