[PATCH Part1 RFC v4 28/36] x86/compressed/64: store Confidential Computing blob address in bootparams

Brijesh Singh
2021-07-07T18:17:05Z

From: Michael Roth <michael.roth@amd.com>

When the Confidential Computing blob is located by the boot/compressed
kernel, store a pointer to it in bootparams->cc_blob_address to avoid
the need for the run-time kernel to rescan the EFI config table to find
it again.

Since this function is also shared by the run-time kernel, this patch
also adds the logic to make use of bootparams->cc_blob_address when it
has been initialized.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/kernel/sev-shared.c | 38 +++++++++++++++++++++++++-----------
1 file changed, 27 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 5e0e8e208a8c..23328727caf4 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -820,7 +820,6 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
return ES_OK;
}

-#ifdef BOOT_COMPRESSED
static struct setup_data *get_cc_setup_data(struct boot_params *bp)
{
struct setup_data *hdr = (struct setup_data *)bp->hdr.setup_data;
@@ -840,6 +839,16 @@ static struct setup_data *get_cc_setup_data(struct boot_params *bp)
* 1) Search for CC blob in the following order/precedence:
* - via linux boot protocol / setup_data entry
* - via EFI configuration table
+ * 2) If found, initialize boot_params->cc_blob_address to point to the
+ * blob so that uncompressed kernel can easily access it during very
+ * early boot without the need to re-parse EFI config table
+ * 3) Return a pointer to the CC blob, NULL otherwise.
+ *
+ * For run-time/uncompressed kernel:
+ *
+ * 1) Search for CC blob in the following order/precedence:
+ * - via linux boot protocol / setup_data entry
+ * - via boot_params->cc_blob_address
* 2) Return a pointer to the CC blob, NULL otherwise.
*/
static struct cc_blob_sev_info *sev_snp_probe_cc_blob(struct boot_params *bp)
@@ -857,27 +866,34 @@ static struct cc_blob_sev_info *sev_snp_probe_cc_blob(struct boot_params *bp)
goto out_verify;
}

+#ifdef __BOOT_COMPRESSED
/* CC blob isn't in setup_data, see if it's in the EFI config table */
(void)efi_bp_find_vendor_table(bp, EFI_CC_BLOB_GUID,
(unsigned long *)&cc_info);
+#else
+ /*
+ * CC blob isn't in setup_data, see if boot kernel passed it via
+ * boot_params.
+ */
+ if (bp->cc_blob_address)
+ cc_info = (struct cc_blob_sev_info *)(unsigned long)bp->cc_blob_address;
+#endif

out_verify:
/* CC blob should be either valid or not present. Fail otherwise. */
if (cc_info && cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
sev_es_terminate(1, GHCB_SNP_UNSUPPORTED);

+#ifdef __BOOT_COMPRESSED
+ /*
+ * Pass run-time kernel a pointer to CC info via boot_params for easier
+ * access during early boot.
+ */
+ bp->cc_blob_address = (u32)(unsigned long)cc_info;
+#endif
+
return cc_info;
}
-#else
-/*
- * Probing for CC blob for run-time kernel will be enabled in a subsequent
- * patch. For now we need to stub this out.
- */
-static struct cc_blob_sev_info *sev_snp_probe_cc_blob(struct boot_params *bp)
-{
- return NULL;
-}
-#endif

/*
* Initial set up of CPUID table when running identity-mapped.
--
2.17.1