Re: [PATCH v13 19/19] x86/efi: EFI stub DRTM launch support for Secure Launch

[H. Peter Anvin]

On March 28, 2025 4:08:14 PM PDT, Ross Philipson <ross.philipson@xxxxxxxxxx> wrote:
>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@xxxxxxxxxx>
>Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
>---
> 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 d96d4494070d..bbbc4b327ce1 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 863910e9eefc..033133e7d953 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>
>@@ -798,6 +800,93 @@ 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.

efi_set_u64_form()?

What the heck is that? If it actually involves two u32 packed into a 64 field, why not simply do two stores?