[PATCH v2 3/4] efi_loader: check lowest supported version in capsule update

[Masahisa Kojima]

The FMP Payload Header which EDK2 capsule generation scripts
insert contains lowest supported version.
This commit reads the lowest supported version stored in the
"FmpStateXXXX" EFI non-volatile variable, then check if the
firmware version of ongoing capsule is equal or greater than
the lowest supported version.

Signed-off-by: Masahisa Kojima <masahisa.kojima at linaro.org>
---
Changes in v2:
- add error message when the firmware version is lower than
  lowest supported version

 lib/efi_loader/efi_firmware.c | 45 ++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/lib/efi_loader/efi_firmware.c b/lib/efi_loader/efi_firmware.c
index ead20fa914..fc6babfc34 100644
--- a/lib/efi_loader/efi_firmware.c
+++ b/lib/efi_loader/efi_firmware.c
@@ -368,6 +368,34 @@ void efi_firmware_parse_payload_header(const void **p_image,
 	*p_image_size = image_size;
 }
 
+/**
+ * efi_firmware_get_lowest_supported_version - get the lowest supported version
+ * @image_index:	image_index
+ *
+ * Get the lowest supported version from FmpStateXXXX variable.
+ *
+ * Return:		lowest supported version, return 0 if reading FmpStateXXXX
+ *			variable failed
+ */
+static
+u32 efi_firmware_get_lowest_supported_version(u8 image_index)
+{
+	u16 varname[13]; /* u"FmpStateXXXX" */
+	efi_status_t ret;
+	efi_uintn_t size;
+	struct fmp_state var_state = { 0 };
+
+	efi_create_indexed_name(varname, sizeof(varname), "FmpState",
+				image_index);
+	size = sizeof(var_state);
+	ret = efi_get_variable_int(varname, &efi_guid_fmp_state, NULL, &size,
+				   &var_state, NULL);
+	if (ret != EFI_SUCCESS)
+		return 0;
+
+	return var_state.lowest_supported_version;
+}
+
 /**
  * efi_firmware_verify_image - verify image
  * @p_image:		Pointer to new image
@@ -375,7 +403,8 @@ void efi_firmware_parse_payload_header(const void **p_image,
  * @image_index		Image index
  * @state		Pointer to fmp state
  *
- * Verify the capsule file
+ * Verify the capsule authentication and check if the fw_version
+ * is equal or greater than the lowest supported version.
  *
  * Return:		status code
  */
@@ -386,10 +415,24 @@ efi_status_t efi_firmware_verify_image(const void **p_image,
 				       struct fmp_state *state)
 {
 	efi_status_t ret;
+	u32 lowest_supported_version;
 
 	ret = efi_firmware_capsule_authenticate(p_image, p_image_size, state);
 	efi_firmware_parse_payload_header(p_image, p_image_size, state);
 
+	/* check lowest_supported_version if capsule authentication passes */
+	if (ret == EFI_SUCCESS) {
+		lowest_supported_version =
+			efi_firmware_get_lowest_supported_version(image_index);
+		if (lowest_supported_version > state->fw_version) {
+			printf("fw_version(%u) is too low(expected >%u). Aborting update\n",
+			       state->fw_version, lowest_supported_version);
+			state->last_attempt_status =
+				LAST_ATTEMPT_STATUS_ERROR_INCORRECT_VERSION;
+			ret = EFI_INVALID_PARAMETER;
+		}
+	}
+
 	return ret;
 }
 
-- 
2.17.1