[PATCH Part1 RFC v4 27/36] x86/boot: add a pointer to Confidential Computing blob in bootparams

[Brijesh Singh]

From: Michael Roth <michael.roth@xxxxxxx>

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@xxxxxxx>
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 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