[v3,05/16] efi_loader: variable: support variable authentication
diff mbox series

Message ID 20191209060056.32426-6-takahiro.akashi@linaro.org
State Superseded
Delegated to: Heinrich Schuchardt
Headers show
Series
  • efi_loader: add secure boot support
Related show

Commit Message

AKASHI Takahiro Dec. 9, 2019, 6 a.m. UTC
With this commit, EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS
is supported for authenticated variables and the system secure state
will transfer between setup mode and user mode as UEFI specification
section 32.3 describes.

Internally, authentication data is stored as part of authenticated
variable's value. It is nothing but a pkcs7 message (but we need some
wrapper, see efi_variable_parse_signature()) and will be validated by
efi_variable_authenticate(), hence efi_signature_verify_with_db().

Associated time value will be encoded in "{...,time=...}" along with
other UEFI variable's attributes.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
---
 include/efi_loader.h          |   3 +
 lib/efi_loader/efi_variable.c | 665 ++++++++++++++++++++++++++++------
 2 files changed, 564 insertions(+), 104 deletions(-)

Patch
diff mbox series

diff --git a/include/efi_loader.h b/include/efi_loader.h
index 3b3618e0be24..1f88caf86709 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -175,6 +175,7 @@  extern const efi_guid_t efi_guid_image_security_database;
 extern const efi_guid_t efi_guid_sha256;
 extern const efi_guid_t efi_guid_cert_x509;
 extern const efi_guid_t efi_guid_cert_x509_sha256;
+extern const efi_guid_t efi_guid_cert_type_pkcs7;
 
 extern unsigned int __efi_runtime_start, __efi_runtime_stop;
 extern unsigned int __efi_runtime_rel_start, __efi_runtime_rel_stop;
@@ -723,6 +724,8 @@  efi_status_t efi_image_region_add(struct efi_image_regions *regs,
 
 void efi_sigstore_free(struct efi_signature_store *sigstore);
 struct efi_signature_store *efi_sigstore_parse_sigdb(u16 *name);
+
+bool efi_secure_boot_enabled(void);
 #endif /* CONFIG_EFI_SECURE_BOOT */
 
 #else /* CONFIG_IS_ENABLED(EFI_LOADER) */
diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
index 46f35bc60ba0..171b4abb4c58 100644
--- a/lib/efi_loader/efi_variable.c
+++ b/lib/efi_loader/efi_variable.c
@@ -10,7 +10,13 @@ 
 #include <env_internal.h>
 #include <hexdump.h>
 #include <malloc.h>
+#include <rtc.h>
 #include <search.h>
+#include <linux/compat.h>
+#include "../lib/crypto/pkcs7_parser.h"
+
+const efi_guid_t efi_guid_cert_type_pkcs7 = EFI_CERT_TYPE_PKCS7_GUID;
+static bool efi_secure_boot;
 
 #define READ_ONLY BIT(31)
 
@@ -107,7 +113,7 @@  static const char *prefix(const char *str, const char *prefix)
  * @attrp:	pointer to UEFI attributes
  * Return:	pointer to remainder of U-Boot variable value
  */
-static const char *parse_attr(const char *str, u32 *attrp)
+static const char *parse_attr(const char *str, u32 *attrp, u64 *timep)
 {
 	u32 attr = 0;
 	char sep = '{';
@@ -130,6 +136,12 @@  static const char *parse_attr(const char *str, u32 *attrp)
 			attr |= EFI_VARIABLE_BOOTSERVICE_ACCESS;
 		} else if ((s = prefix(str, "run"))) {
 			attr |= EFI_VARIABLE_RUNTIME_ACCESS;
+		} else if ((s = prefix(str, "time="))) {
+			attr |= EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS;
+			hex2bin((u8 *)timep, s, sizeof(*timep));
+			s += sizeof(*timep) * 2;
+		} else if (*str == '}') {
+			break;
 		} else {
 			printf("invalid attribute: %s\n", str);
 			break;
@@ -147,48 +159,291 @@  static const char *parse_attr(const char *str, u32 *attrp)
 }
 
 /**
- * efi_get_variable() - retrieve value of a UEFI variable
+ * efi_secure_boot_enabled - return if secure boot is enabled or not
  *
- * This function implements the GetVariable runtime service.
+ * Return:	true if enabled, false if disabled
+ */
+bool efi_secure_boot_enabled(void)
+{
+	return efi_secure_boot;
+}
+
+#ifdef CONFIG_EFI_SECURE_BOOT
+static u8 pkcs7_hdr[] = {
+	/* SEQUENCE */
+	0x30, 0x82, 0x05, 0xc7,
+	/* OID: pkcs7-signedData */
+	0x06, 0x09, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x01, 0x07, 0x02,
+	/* Context Structured? */
+	0xa0, 0x82, 0x05, 0xb8,
+};
+
+/**
+ * efi_variable_parse_signature - parse a signature in variable
+ * @buf:	Pointer to variable's value
+ * @buflen:	Length of @buf
  *
- * See the Unified Extensible Firmware Interface (UEFI) specification for
- * details.
+ * Parse a signature embedded in variable's value and instantiate
+ * a pkcs7_message structure. Since pkcs7_parse_message() accepts only
+ * pkcs7's signedData, some header needed be prepended for correctly
+ * parsing authentication data, particularly for variable's.
  *
- * @variable_name:	name of the variable
- * @vendor:		vendor GUID
- * @attributes:		attributes of the variable
- * @data_size:		size of the buffer to which the variable value is copied
- * @data:		buffer to which the variable value is copied
- * Return:		status code
+ * Return:	Pointer to pkcs7_message structure on success, NULL on error
  */
-efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
-				     const efi_guid_t *vendor, u32 *attributes,
-				     efi_uintn_t *data_size, void *data)
+static struct pkcs7_message *efi_variable_parse_signature(const void *buf,
+							  size_t buflen)
+{
+	u8 *ebuf;
+	size_t ebuflen, len;
+	struct pkcs7_message *msg;
+
+	/*
+	 * This is the best assumption to check if the binary is
+	 * already in a form of pkcs7's signedData.
+	 */
+	if (buflen > sizeof(pkcs7_hdr) &&
+	    !memcmp(&((u8 *)buf)[4], &pkcs7_hdr[4], 11)) {
+		msg = pkcs7_parse_message(buf, buflen);
+		goto out;
+	}
+
+	/*
+	 * Otherwise, we should add a dummy prefix sequence for pkcs7
+	 * message parser to be able to process.
+	 * NOTE: EDK2 also uses similar hack in WrapPkcs7Data()
+	 * in CryptoPkg/Library/BaseCryptLib/Pk/CryptPkcs7VerifyCommon.c
+	 * TODO:
+	 * The header should be composed in a more refined manner.
+	 */
+	debug("Makeshift prefix added to authentication data\n");
+	ebuflen = sizeof(pkcs7_hdr) + buflen;
+	if (ebuflen <= 0x7f) {
+		debug("Data is too short\n");
+		return NULL;
+	}
+
+	ebuf = malloc(ebuflen);
+	if (!ebuf) {
+		debug("Out of memory\n");
+		return NULL;
+	}
+
+	memcpy(ebuf, pkcs7_hdr, sizeof(pkcs7_hdr));
+	memcpy(ebuf + sizeof(pkcs7_hdr), buf, buflen);
+	len = ebuflen - 4;
+	ebuf[2] = (len >> 8) & 0xff;
+	ebuf[3] = len & 0xff;
+	len = ebuflen - 0x13;
+	ebuf[0x11] = (len >> 8) & 0xff;
+	ebuf[0x12] = len & 0xff;
+
+	msg = pkcs7_parse_message(ebuf, ebuflen);
+
+	free(ebuf);
+
+out:
+	if (IS_ERR(msg))
+		return NULL;
+
+	return msg;
+}
+
+/**
+ * efi_variable_authenticate - authenticate a variable
+ * @variable:	Variable name in u16
+ * @vendor:	Guid of variable
+ * @data_size:	Size of @data
+ * @data:	Pointer to variable's value
+ * @given_attr:	Attributes to be given at SetVariable()
+ * @env_attr:	Attributes that an existing variable holds
+ * @time:	signed time that an existing variable holds
+ *
+ * Called by efi_set_variable() to verify that the input is correct.
+ * Will replace the given data pointer with another that points to
+ * the actual data to store in the internal memory.
+ * On success, @data and @data_size will be replaced with variable's
+ * actual data, excluding authentication data, and its size, and variable's
+ * attributes and signed time will also be returned in @env_attr and @time,
+ * respectively.
+ *
+ * Return:	EFI_SUCCESS on success, status code (negative) on error
+ */
+static efi_status_t efi_variable_authenticate(u16 *variable,
+					      const efi_guid_t *vendor,
+					      efi_uintn_t *data_size,
+					      const void **data, u32 given_attr,
+					      u32 *env_attr, u64 *time)
+{
+	const struct efi_variable_authentication_2 *auth;
+	struct efi_signature_store *truststore, *truststore2;
+	struct pkcs7_message *var_sig;
+	struct efi_image_regions *regs;
+	const struct efi_time *timestamp;
+	struct rtc_time tm;
+	u64 new_time;
+	efi_status_t ret;
+
+	var_sig = NULL;
+	truststore = NULL;
+	truststore2 = NULL;
+	regs = NULL;
+	ret = EFI_SECURITY_VIOLATION;
+
+	if (*data_size < sizeof(struct efi_variable_authentication_2))
+		goto err;
+
+	/* authentication data */
+	auth = *data;
+	if (*data_size < (sizeof(auth->time_stamp)
+				+ auth->auth_info.hdr.dwLength))
+		goto err;
+
+	if (guidcmp(&auth->auth_info.cert_type, &efi_guid_cert_type_pkcs7))
+		goto err;
+
+	*data += sizeof(auth->time_stamp) + auth->auth_info.hdr.dwLength;
+	*data_size -= (sizeof(auth->time_stamp)
+				+ auth->auth_info.hdr.dwLength);
+
+	timestamp = &auth->time_stamp;
+	memset(&tm, 0, sizeof(tm));
+	tm.tm_year = timestamp->year;
+	tm.tm_mon = timestamp->month;
+	tm.tm_mday = timestamp->day;
+	tm.tm_hour = timestamp->hour;
+	tm.tm_min = timestamp->minute;
+	tm.tm_sec = timestamp->second;
+	new_time = rtc_mktime(&tm);
+
+	if (!efi_secure_boot_enabled()) {
+		/* finished checking */
+		*time = new_time;
+		return EFI_SUCCESS;
+	}
+
+	if (new_time <= *time)
+		goto err;
+
+	/* data to be digested */
+	regs = calloc(sizeof(*regs) + sizeof(struct image_region) * 5, 1);
+	if (!regs)
+		goto err;
+	regs->max = 5;
+	efi_image_region_add(regs, (uint8_t *)variable,
+			     (uint8_t *)variable
+				+ u16_strlen(variable) * sizeof(u16), 1);
+	efi_image_region_add(regs, (uint8_t *)vendor,
+			     (uint8_t *)vendor + sizeof(*vendor), 1);
+	efi_image_region_add(regs, (uint8_t *)&given_attr,
+			     (uint8_t *)&given_attr + sizeof(given_attr), 1);
+	efi_image_region_add(regs, (uint8_t *)timestamp,
+			     (uint8_t *)timestamp + sizeof(*timestamp), 1);
+	efi_image_region_add(regs, (uint8_t *)*data,
+			     (uint8_t *)*data + *data_size, 1);
+
+	/* variable's signature list */
+	if (auth->auth_info.hdr.dwLength < sizeof(auth->auth_info))
+		goto err;
+	var_sig = efi_variable_parse_signature(auth->auth_info.cert_data,
+					       auth->auth_info.hdr.dwLength
+						   - sizeof(auth->auth_info));
+	if (IS_ERR(var_sig)) {
+		debug("Parsing variable's signature failed\n");
+		var_sig = NULL;
+		goto err;
+	}
+
+	/* signature database used for authentication */
+	if (u16_strcmp(variable, L"PK") == 0 ||
+	    u16_strcmp(variable, L"KEK") == 0) {
+		/* with PK */
+		truststore = efi_sigstore_parse_sigdb(L"PK");
+		if (!truststore)
+			goto err;
+	} else if (u16_strcmp(variable, L"db") == 0 ||
+		   u16_strcmp(variable, L"dbx") == 0) {
+		/* with PK and KEK */
+		truststore = efi_sigstore_parse_sigdb(L"KEK");
+		truststore2 = efi_sigstore_parse_sigdb(L"PK");
+
+		if (!truststore) {
+			if (!truststore2)
+				goto err;
+
+			truststore = truststore2;
+			truststore2 = NULL;
+		}
+	} else {
+		/* TODO: support private authenticated variables */
+		goto err;
+	}
+
+	/* verify signature */
+	if (efi_signature_verify_with_sigdb(regs, var_sig, truststore, NULL)) {
+		debug("Verified\n");
+	} else {
+		if (truststore2 &&
+		    efi_signature_verify_with_sigdb(regs, var_sig,
+						    truststore2, NULL)) {
+			debug("Verified\n");
+		} else {
+			debug("Verifying variable's signature failed\n");
+			goto err;
+		}
+	}
+
+	/* finished checking */
+	*time = rtc_mktime(&tm);
+	ret = EFI_SUCCESS;
+
+err:
+	efi_sigstore_free(truststore);
+	efi_sigstore_free(truststore2);
+	pkcs7_free_message(var_sig);
+	free(regs);
+
+	return ret;
+}
+#else
+static efi_status_t efi_variable_authenticate(u16 *variable,
+					      const efi_guid_t *vendor,
+					      efi_uintn_t *data_size,
+					      const void **data, u32 given_attr,
+					      u32 *env_attr, u64 *time)
+{
+	return EFI_SUCCESS;
+}
+#endif /* CONFIG_EFI_SECURE_BOOT */
+
+static
+efi_status_t EFIAPI efi_get_variable_common(u16 *variable_name,
+					    const efi_guid_t *vendor,
+					    u32 *attributes,
+					    efi_uintn_t *data_size, void *data,
+					    bool is_non_volatile)
 {
 	char *native_name;
 	efi_status_t ret;
 	unsigned long in_size;
-	const char *val, *s;
+	const char *val = NULL, *s;
+	u64 time = 0;
 	u32 attr;
 
-	EFI_ENTRY("\"%ls\" %pUl %p %p %p", variable_name, vendor, attributes,
-		  data_size, data);
-
 	if (!variable_name || !vendor || !data_size)
 		return EFI_EXIT(EFI_INVALID_PARAMETER);
 
 	ret = efi_to_native(&native_name, variable_name, vendor);
 	if (ret)
-		return EFI_EXIT(ret);
+		return ret;
 
 	EFI_PRINT("get '%s'\n", native_name);
 
 	val = env_get(native_name);
 	free(native_name);
 	if (!val)
-		return EFI_EXIT(EFI_NOT_FOUND);
+		return EFI_NOT_FOUND;
 
-	val = parse_attr(val, &attr);
+	val = parse_attr(val, &attr, &time);
 
 	in_size = *data_size;
 
@@ -197,7 +452,7 @@  efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
 
 		/* number of hexadecimal digits must be even */
 		if (len & 1)
-			return EFI_EXIT(EFI_DEVICE_ERROR);
+			return EFI_DEVICE_ERROR;
 
 		/* two characters per byte: */
 		len /= 2;
@@ -208,11 +463,13 @@  efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
 			goto out;
 		}
 
-		if (!data)
-			return EFI_EXIT(EFI_INVALID_PARAMETER);
+		if (!data) {
+			debug("Variable with no data shouldn't exist.\n");
+			return EFI_INVALID_PARAMETER;
+		}
 
 		if (hex2bin(data, s, len))
-			return EFI_EXIT(EFI_DEVICE_ERROR);
+			return EFI_DEVICE_ERROR;
 
 		EFI_PRINT("got value: \"%s\"\n", s);
 	} else if ((s = prefix(val, "(utf8)"))) {
@@ -225,8 +482,10 @@  efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
 			goto out;
 		}
 
-		if (!data)
-			return EFI_EXIT(EFI_INVALID_PARAMETER);
+		if (!data) {
+			debug("Variable with no data shouldn't exist.\n");
+			return EFI_INVALID_PARAMETER;
+		}
 
 		memcpy(data, s, len);
 		((char *)data)[len] = '\0';
@@ -234,13 +493,67 @@  efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
 		EFI_PRINT("got value: \"%s\"\n", (char *)data);
 	} else {
 		EFI_PRINT("invalid value: '%s'\n", val);
-		return EFI_EXIT(EFI_DEVICE_ERROR);
+		return EFI_DEVICE_ERROR;
 	}
 
 out:
 	if (attributes)
 		*attributes = attr & EFI_VARIABLE_MASK;
 
+	return ret;
+}
+
+static
+efi_status_t EFIAPI efi_get_volatile_variable(u16 *variable_name,
+					      const efi_guid_t *vendor,
+					      u32 *attributes,
+					      efi_uintn_t *data_size,
+					      void *data)
+{
+	return efi_get_variable_common(variable_name, vendor, attributes,
+				       data_size, data, false);
+}
+
+efi_status_t EFIAPI efi_get_nonvolatile_variable(u16 *variable_name,
+						 const efi_guid_t *vendor,
+						 u32 *attributes,
+						 efi_uintn_t *data_size,
+						 void *data)
+{
+	return efi_get_variable_common(variable_name, vendor, attributes,
+				       data_size, data, true);
+}
+
+/**
+ * efi_efi_get_variable() - retrieve value of a UEFI variable
+ *
+ * This function implements the GetVariable runtime service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @variable_name:	name of the variable
+ * @vendor:		vendor GUID
+ * @attributes:		attributes of the variable
+ * @data_size:		size of the buffer to which the variable value is copied
+ * @data:		buffer to which the variable value is copied
+ * Return:		status code
+ */
+efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
+				     const efi_guid_t *vendor, u32 *attributes,
+				     efi_uintn_t *data_size, void *data)
+{
+	efi_status_t ret;
+
+	EFI_ENTRY("\"%ls\" %pUl %p %p %p", variable_name, vendor, attributes,
+		  data_size, data);
+
+	ret = efi_get_volatile_variable(variable_name, vendor, attributes,
+					data_size, data);
+	if (ret == EFI_NOT_FOUND)
+		ret = efi_get_nonvolatile_variable(variable_name, vendor,
+						   attributes, data_size, data);
+
 	return EFI_EXIT(ret);
 }
 
@@ -273,6 +586,7 @@  static efi_status_t parse_uboot_variable(char *variable,
 {
 	char *guid, *name, *end, c;
 	unsigned long name_len;
+	u64 time;
 	u16 *p;
 
 	guid = strchr(variable, '_');
@@ -307,7 +621,7 @@  static efi_status_t parse_uboot_variable(char *variable,
 	*(name - 1) = c;
 
 	/* attributes */
-	parse_attr(end, attributes);
+	parse_attr(end, attributes, &time);
 
 	return EFI_SUCCESS;
 }
@@ -389,7 +703,7 @@  efi_status_t EFIAPI efi_get_next_variable_name(efi_uintn_t *variable_name_size,
 		list_len = hexport_r(&env_htab, '\n',
 				     H_MATCH_REGEX | H_MATCH_KEY,
 				     &efi_variables_list, 0, 1, regexlist);
-		/* 1 indicates that no match was found */
+
 		if (list_len <= 1)
 			return EFI_EXIT(EFI_NOT_FOUND);
 
@@ -402,143 +716,286 @@  efi_status_t EFIAPI efi_get_next_variable_name(efi_uintn_t *variable_name_size,
 	return EFI_EXIT(ret);
 }
 
-/**
- * efi_set_variable() - set value of a UEFI variable
- *
- * This function implements the SetVariable runtime service.
- *
- * See the Unified Extensible Firmware Interface (UEFI) specification for
- * details.
- *
- * @variable_name:	name of the variable
- * @vendor:		vendor GUID
- * @attributes:		attributes of the variable
- * @data_size:		size of the buffer with the variable value
- * @data:		buffer with the variable value
- * Return:		status code
- */
-efi_status_t EFIAPI efi_set_variable(u16 *variable_name,
-				     const efi_guid_t *vendor, u32 attributes,
-				     efi_uintn_t data_size, const void *data)
+static
+efi_status_t EFIAPI efi_set_variable_common(u16 *variable_name,
+					    const efi_guid_t *vendor,
+					    u32 attributes,
+					    efi_uintn_t data_size,
+					    const void *data,
+					    bool ro_check,
+					    bool is_non_volatile)
 {
-	char *native_name = NULL, *val = NULL, *s;
-	const char *old_val;
-	size_t old_size;
-	efi_status_t ret = EFI_SUCCESS;
+	char *native_name = NULL, *old_data = NULL, *val = NULL, *s;
+	efi_uintn_t old_size;
+	bool append, delete;
+	u64 time = 0;
 	u32 attr;
+	efi_status_t ret = EFI_SUCCESS;
 
-	EFI_ENTRY("\"%ls\" %pUl %x %zu %p", variable_name, vendor, attributes,
-		  data_size, data);
+	debug("%s: set '%s'\n", __func__, native_name);
 
 	if (!variable_name || !*variable_name || !vendor ||
 	    ((attributes & EFI_VARIABLE_RUNTIME_ACCESS) &&
 	     !(attributes & EFI_VARIABLE_BOOTSERVICE_ACCESS))) {
 		ret = EFI_INVALID_PARAMETER;
-		goto out;
+		goto err;
 	}
 
 	ret = efi_to_native(&native_name, variable_name, vendor);
 	if (ret)
-		goto out;
+		goto err;
+
+	/* check if a variable exists */
+	old_size = 0;
+	attr = 0;
+	ret = EFI_CALL(efi_get_variable(variable_name, vendor, &attr,
+					&old_size, NULL));
+	if (ret == EFI_BUFFER_TOO_SMALL) {
+		if ((is_non_volatile && !(attr & EFI_VARIABLE_NON_VOLATILE)) ||
+		    (!is_non_volatile && (attr & EFI_VARIABLE_NON_VOLATILE))) {
+			ret = EFI_INVALID_PARAMETER;
+			goto err;
+		}
+	}
 
-	old_val = env_get(native_name);
-	if (old_val) {
-		old_val = parse_attr(old_val, &attr);
+	append = !!(attributes & EFI_VARIABLE_APPEND_WRITE);
+	attributes &= ~(u32)EFI_VARIABLE_APPEND_WRITE;
+	delete = !append && (!data_size || !attributes);
 
-		/* check read-only first */
-		if (attr & READ_ONLY) {
+	/* check attributes */
+	if (old_size) {
+		if (ro_check && (attr & READ_ONLY)) {
 			ret = EFI_WRITE_PROTECTED;
-			goto out;
-		}
-
-		if ((data_size == 0 &&
-		     !(attributes & EFI_VARIABLE_APPEND_WRITE)) ||
-		    !attributes) {
-			/* delete the variable: */
-			env_set(native_name, NULL);
-			ret = EFI_SUCCESS;
-			goto out;
+			goto err;
 		}
 
 		/* attributes won't be changed */
-		if (attr != (attributes & ~EFI_VARIABLE_APPEND_WRITE)) {
+		if (!delete &&
+		    ((ro_check && attr != attributes) ||
+		     (!ro_check && ((attr & ~(u32)READ_ONLY)
+				    != (attributes & ~(u32)READ_ONLY))))) {
 			ret = EFI_INVALID_PARAMETER;
-			goto out;
-		}
-
-		if (attributes & EFI_VARIABLE_APPEND_WRITE) {
-			if (!prefix(old_val, "(blob)")) {
-				ret = EFI_DEVICE_ERROR;
-				goto out;
-			}
-			old_size = strlen(old_val);
-		} else {
-			old_size = 0;
+			goto err;
 		}
 	} else {
-		if (data_size == 0 || !attributes ||
-		    (attributes & EFI_VARIABLE_APPEND_WRITE)) {
+		if (delete || append) {
 			/*
 			 * Trying to delete or to update a non-existent
 			 * variable.
 			 */
 			ret = EFI_NOT_FOUND;
-			goto out;
+			goto err;
+		}
+	}
+
+	if (((!u16_strcmp(variable_name, L"PK") ||
+	      !u16_strcmp(variable_name, L"KEK")) &&
+		!guidcmp(vendor, &efi_global_variable_guid)) ||
+	    ((!u16_strcmp(variable_name, L"db") ||
+	      !u16_strcmp(variable_name, L"dbx")) &&
+		!guidcmp(vendor, &efi_guid_image_security_database))) {
+		/* authentication is mandatory */
+		if (!(attributes &
+		      EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS)) {
+			debug("%ls: AUTHENTICATED_WRITE_ACCESS required\n",
+			      variable_name);
+			ret = EFI_INVALID_PARAMETER;
+			goto err;
 		}
+	}
+
+	/* authenticate a variable */
+	if (IS_ENABLED(CONFIG_EFI_SECURE_BOOT)) {
+		if (attributes & EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS) {
+			ret = EFI_INVALID_PARAMETER;
+			goto err;
+		}
+		if (attributes &
+		    EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS) {
+			ret = efi_variable_authenticate(variable_name, vendor,
+							&data_size, &data,
+							attributes, &attr,
+							&time);
+			if (ret != EFI_SUCCESS)
+				goto err;
+
+			/* last chance to check for delete */
+			if (!data_size)
+				delete = true;
+		}
+	} else {
+		if (attributes &
+		    (EFI_VARIABLE_AUTHENTICATED_WRITE_ACCESS |
+		     EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS)) {
+			debug("Secure boot is not configured\n");
+			ret = EFI_INVALID_PARAMETER;
+			goto err;
+		}
+	}
+
+	/* delete a variable */
+	if (delete) {
+		/* !old_size case has been handled before */
+		val = NULL;
+		ret = EFI_SUCCESS;
+		goto out;
+	}
 
+	if (append) {
+		old_data = malloc(old_size);
+		if (!old_data) {
+			return EFI_OUT_OF_RESOURCES;
+			goto err;
+		}
+		ret = EFI_CALL(efi_get_variable(variable_name, vendor,
+						&attr, &old_size, old_data));
+		if (ret != EFI_SUCCESS)
+			goto err;
+	} else {
 		old_size = 0;
 	}
 
-	val = malloc(old_size + 2 * data_size
-		     + strlen("{ro,run,boot,nv}(blob)") + 1);
+	val = malloc(2 * old_size + 2 * data_size
+		     + strlen("{ro,run,boot,nv,time=0123456701234567}(blob)")
+		     + 1);
 	if (!val) {
 		ret = EFI_OUT_OF_RESOURCES;
-		goto out;
+		goto err;
 	}
 
 	s = val;
 
-	/* store attributes */
-	attributes &= (EFI_VARIABLE_NON_VOLATILE |
+	/*
+	 * store attributes
+	 */
+	attributes &= (READ_ONLY |
+		       EFI_VARIABLE_NON_VOLATILE |
 		       EFI_VARIABLE_BOOTSERVICE_ACCESS |
-		       EFI_VARIABLE_RUNTIME_ACCESS);
+		       EFI_VARIABLE_RUNTIME_ACCESS |
+		       EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS);
 	s += sprintf(s, "{");
 	while (attributes) {
-		u32 attr = 1 << (ffs(attributes) - 1);
+		attr = 1 << (ffs(attributes) - 1);
 
-		if (attr == EFI_VARIABLE_NON_VOLATILE)
+		if (attr == READ_ONLY) {
+			s += sprintf(s, "ro");
+		} else if (attr == EFI_VARIABLE_NON_VOLATILE) {
 			s += sprintf(s, "nv");
-		else if (attr == EFI_VARIABLE_BOOTSERVICE_ACCESS)
+		} else if (attr == EFI_VARIABLE_BOOTSERVICE_ACCESS) {
 			s += sprintf(s, "boot");
-		else if (attr == EFI_VARIABLE_RUNTIME_ACCESS)
+		} else if (attr == EFI_VARIABLE_RUNTIME_ACCESS) {
 			s += sprintf(s, "run");
+		} else if (attr ==
+			   EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS) {
+			s += sprintf(s, "time=");
+			s = bin2hex(s, (u8 *)&time, sizeof(time));
+		}
 
 		attributes &= ~attr;
 		if (attributes)
 			s += sprintf(s, ",");
 	}
 	s += sprintf(s, "}");
-
-	if (old_size)
-		/* APPEND_WRITE */
-		s += sprintf(s, old_val);
-	else
-		s += sprintf(s, "(blob)");
+	s += sprintf(s, "(blob)");
 
 	/* store payload: */
+	if (append)
+		s = bin2hex(s, old_data, old_size);
 	s = bin2hex(s, data, data_size);
 	*s = '\0';
 
 	EFI_PRINT("setting: %s=%s\n", native_name, val);
 
+out:
 	if (env_set(native_name, val))
 		ret = EFI_DEVICE_ERROR;
+	else
+		ret = EFI_SUCCESS;
 
-out:
+err:
 	free(native_name);
+	free(old_data);
 	free(val);
 
-	return EFI_EXIT(ret);
+	return ret;
+}
+
+static
+efi_status_t EFIAPI efi_set_volatile_variable(u16 *variable_name,
+					      const efi_guid_t *vendor,
+					      u32 attributes,
+					      efi_uintn_t data_size,
+					      const void *data,
+					      bool ro_check)
+{
+	return efi_set_variable_common(variable_name, vendor, attributes,
+				       data_size, data, ro_check, false);
+}
+
+efi_status_t EFIAPI efi_set_nonvolatile_variable(u16 *variable_name,
+						 const efi_guid_t *vendor,
+						 u32 attributes,
+						 efi_uintn_t data_size,
+						 const void *data,
+						 bool ro_check)
+{
+	efi_status_t ret;
+
+	ret = efi_set_variable_common(variable_name, vendor, attributes,
+				      data_size, data, ro_check, true);
+
+	return ret;
+}
+
+static efi_status_t efi_set_variable_internal(u16 *variable_name,
+					      const efi_guid_t *vendor,
+					      u32 attributes,
+					      efi_uintn_t data_size,
+					      const void *data,
+					      bool ro_check)
+{
+	efi_status_t ret;
+
+	if (attributes & EFI_VARIABLE_NON_VOLATILE)
+		ret = efi_set_nonvolatile_variable(variable_name, vendor,
+						   attributes,
+						   data_size, data, ro_check);
+	else
+		ret = efi_set_volatile_variable(variable_name, vendor,
+						attributes, data_size, data,
+						ro_check);
+
+	return ret;
+}
+
+/**
+ * efi_set_variable() - set value of a UEFI variable
+ *
+ * This function implements the SetVariable runtime service.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @variable_name:	name of the variable
+ * @vendor:		vendor GUID
+ * @attributes:		attributes of the variable
+ * @data_size:		size of the buffer with the variable value
+ * @data:		buffer with the variable value
+ * Return:		status code
+ */
+efi_status_t EFIAPI efi_set_variable(u16 *variable_name,
+				     const efi_guid_t *vendor, u32 attributes,
+				     efi_uintn_t data_size, const void *data)
+{
+	EFI_ENTRY("\"%ls\" %pUl %x %zu %p", variable_name, vendor, attributes,
+		  data_size, data);
+
+	/* READ_ONLY bit is not part of API */
+	attributes &= ~(u32)READ_ONLY;
+
+	return EFI_EXIT(efi_set_variable_internal(variable_name, vendor,
+						  attributes, data_size, data,
+						  true));
 }
 
 /**