[PATCH v14 19/19] x86/efi: EFI stub DRTM launch support for Secure Launch

Ross Philipson
2025-04-21T16:37:04Z

This support allows the DRTM launch to be initiated after an EFI stub
launch of the Linux kernel is done. This is accomplished by providing
a handler to jump to when a Secure Launch is in progress. This has to be
called after the EFI stub does Exit Boot Services.

Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
---
drivers/firmware/efi/libstub/efistub.h | 8 +++
drivers/firmware/efi/libstub/x86-stub.c | 94 +++++++++++++++++++++++++
2 files changed, 102 insertions(+)

diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index f5ba032863a9..6e4cbf02500b 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -135,6 +135,14 @@ void efi_set_u64_split(u64 data, u32 *lo, u32 *hi)
*hi = upper_32_bits(data);
}

+static inline
+void efi_set_u64_form(u32 lo, u32 hi, u64 *data)
+{
+ u64 upper = hi;
+
+ *data = lo | upper << 32;
+}
+
/*
* Allocation types for calls to boottime->allocate_pages.
*/
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index cafc90d4caaf..bfa36466a79c 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -9,6 +9,8 @@
#include <linux/efi.h>
#include <linux/pci.h>
#include <linux/stddef.h>
+#include <linux/slr_table.h>
+#include <linux/slaunch.h>

#include <asm/efi.h>
#include <asm/e820/types.h>
@@ -791,6 +793,93 @@ static efi_status_t efi_decompress_kernel(unsigned long *kernel_entry,
return efi_adjust_memory_range_protection(addr, kernel_text_size);
}

+#if (IS_ENABLED(CONFIG_SECURE_LAUNCH))
+static bool efi_secure_launch_update_boot_params(struct slr_table *slrt,
+ struct boot_params *boot_params)
+{
+ struct slr_entry_intel_info *txt_info;
+ struct slr_entry_policy *policy;
+ bool updated = false;
+ int i;
+
+ txt_info = slr_next_entry_by_tag(slrt, NULL, SLR_ENTRY_INTEL_INFO);
+ if (!txt_info)
+ return false;
+
+ txt_info->boot_params_addr = (u64)boot_params;
+
+ policy = slr_next_entry_by_tag(slrt, NULL, SLR_ENTRY_ENTRY_POLICY);
+ if (!policy)
+ return false;
+
+ for (i = 0; i < policy->nr_entries; i++) {
+ if (policy->policy_entries[i].entity_type == SLR_ET_BOOT_PARAMS) {
+ policy->policy_entries[i].entity = (u64)boot_params;
+ updated = true;
+ break;
+ }
+ }
+
+ /*
+ * If this is a PE entry into EFI stub the mocked up boot params will
+ * be missing some of the setup header data needed for the second stage
+ * of the Secure Launch boot.
+ */
+ if (image) {
+ struct setup_header *hdr = (struct setup_header *)((u8 *)image->image_base +
+ offsetof(struct boot_params, hdr));
+ u64 cmdline_ptr;
+
+ boot_params->hdr.setup_sects = hdr->setup_sects;
+ boot_params->hdr.syssize = hdr->syssize;
+ boot_params->hdr.version = hdr->version;
+ boot_params->hdr.loadflags = hdr->loadflags;
+ boot_params->hdr.kernel_alignment = hdr->kernel_alignment;
+ boot_params->hdr.min_alignment = hdr->min_alignment;
+ boot_params->hdr.xloadflags = hdr->xloadflags;
+ boot_params->hdr.init_size = hdr->init_size;
+ boot_params->hdr.kernel_info_offset = hdr->kernel_info_offset;
+ efi_set_u64_form(boot_params->hdr.cmd_line_ptr, boot_params->ext_cmd_line_ptr,
+ &cmdline_ptr);
+ boot_params->hdr.cmdline_size = strlen((const char *)cmdline_ptr);
+ }
+
+ return updated;
+}
+
+static void efi_secure_launch(struct boot_params *boot_params)
+{
+ struct slr_entry_dl_info *dlinfo;
+ efi_guid_t guid = SLR_TABLE_GUID;
+ dl_handler_func handler_callback;
+ struct slr_table *slrt;
+
+ /*
+ * The presence of this table indicated a Secure Launch
+ * is being requested.
+ */
+ slrt = (struct slr_table *)get_efi_config_table(guid);
+ if (!slrt || slrt->magic != SLR_TABLE_MAGIC)
+ return;
+
+ /*
+ * Since the EFI stub library creates its own boot_params on entry, the
+ * SLRT and TXT heap have to be updated with this version.
+ */
+ if (!efi_secure_launch_update_boot_params(slrt, boot_params))
+ return;
+
+ /* Jump through DL stub to initiate Secure Launch */
+ dlinfo = slr_next_entry_by_tag(slrt, NULL, SLR_ENTRY_DL_INFO);
+
+ handler_callback = (dl_handler_func)dlinfo->dl_handler;
+
+ handler_callback(&dlinfo->bl_context);
+
+ unreachable();
+}
+#endif
+
static void __noreturn enter_kernel(unsigned long kernel_addr,
struct boot_params *boot_params)
{
@@ -925,6 +1014,11 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
goto fail;
}

+#if (IS_ENABLED(CONFIG_SECURE_LAUNCH))
+ /* If a Secure Launch is in progress, this never returns */
+ efi_secure_launch(boot_params);
+#endif
+
/*
* Call the SEV init code while still running with the firmware's
* GDT/IDT, so #VC exceptions will be handled by EFI.
--
2.39.3