efi/libstub: measure loaded initrd info into the TPM

In an effort to ensure the initrd observed and used by the OS is
the same one that was meant to be loaded, which is difficult to
guarantee otherwise, let's measure the initrd if the EFI stub and
specifically the newly introduced LOAD_FILE2 protocol was used.

Modify the initrd loading sequence so that the contents of the initrd
are measured into PCR9.  Note that the patch is currently using
EV_EVENT_TAG to create the eventlog entry instead of EV_IPL.  According
to the TCP PC Client specification this is used for PCRs defined for OS
and application usage.

Co-developed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Link: https://lore.kernel.org/r/20211119114745.1560453-5-ilias.apalodimas@linaro.org
[ardb: add braces to initializer of tagged_event_data]
Link: https://github.com/ClangBuiltLinux/linux/issues/1547
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 58 insertions, 14 deletions

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index 01677181453d..3d972061c1b0 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -625,6 +625,47 @@ efi_status_t efi_load_initrd_cmdline(efi_loaded_image_t *image,
 				    load_addr, load_size);
 }
 
+static const struct {
+	efi_tcg2_event_t	event_data;
+	efi_tcg2_tagged_event_t tagged_event;
+	u8			tagged_event_data[];
+} initrd_tcg2_event = {
+	{
+		sizeof(initrd_tcg2_event) + sizeof("Linux initrd"),
+		{
+			sizeof(initrd_tcg2_event.event_data.event_header),
+			EFI_TCG2_EVENT_HEADER_VERSION,
+			9,
+			EV_EVENT_TAG,
+		},
+	},
+	{
+		INITRD_EVENT_TAG_ID,
+		sizeof("Linux initrd"),
+	},
+	{ "Linux initrd" },
+};
+
+static void efi_measure_initrd(unsigned long load_addr, unsigned long load_size)
+{
+	efi_guid_t tcg2_guid = EFI_TCG2_PROTOCOL_GUID;
+	efi_tcg2_protocol_t *tcg2 = NULL;
+	efi_status_t status;
+
+	efi_bs_call(locate_protocol, &tcg2_guid, NULL, (void **)&tcg2);
+	if (tcg2) {
+		status = efi_call_proto(tcg2, hash_log_extend_event,
+					0, load_addr, load_size,
+					&initrd_tcg2_event.event_data);
+		if (status != EFI_SUCCESS)
+			efi_warn("Failed to measure initrd data: 0x%lx\n",
+				 status);
+		else
+			efi_info("Measured initrd data into PCR %d\n",
+				 initrd_tcg2_event.event_data.event_header.pcr_index);
+	}
+}
+
 /**
  * efi_load_initrd() - Load initial RAM disk
  * @image:	EFI loaded image protocol
@@ -645,22 +686,25 @@ efi_status_t efi_load_initrd(efi_loaded_image_t *image,
 
 	if (efi_noinitrd) {
 		*load_addr = *load_size = 0;
-		return EFI_SUCCESS;
+		status = EFI_SUCCESS;
+	} else {
+		status = efi_load_initrd_dev_path(load_addr, load_size, hard_limit);
+		if (status == EFI_SUCCESS) {
+			efi_info("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n");
+			if (*load_size > 0)
+				efi_measure_initrd(*load_addr, *load_size);
+		} else if (status == EFI_NOT_FOUND) {
+			status = efi_load_initrd_cmdline(image, load_addr, load_size,
+							 soft_limit, hard_limit);
+			if (status == EFI_SUCCESS && *load_size > 0)
+				efi_info("Loaded initrd from command line option\n");
+		}
+		if (status != EFI_SUCCESS) {
+			efi_err("Failed to load initrd: 0x%lx\n", status);
+			*load_addr = *load_size = 0;
+		}
 	}
 
-	status = efi_load_initrd_dev_path(load_addr, load_size, hard_limit);
-	if (status == EFI_SUCCESS) {
-		efi_info("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n");
-	} else if (status == EFI_NOT_FOUND) {
-		status = efi_load_initrd_cmdline(image, load_addr, load_size,
-						 soft_limit, hard_limit);
-		if (status == EFI_SUCCESS && *load_size > 0)
-			efi_info("Loaded initrd from command line option\n");
-	}
-	if (status != EFI_SUCCESS) {
-		efi_err("Failed to load initrd: 0x%lx\n", status);
-		*load_addr = *load_size = 0;
-	}
 	return status;
 }