[PATCH v12 33/46] x86/boot: Add a pointer to Confidential Computing blob in bootparams

Brijesh Singh
2022-03-07T21:35:24Z

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 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
table.

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
table.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
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(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 */
--
2.25.1