[PATCH v4 08/14] boot: image: add FIT decrypt-to-buffer helper
James Hilliard
james.hilliard1 at gmail.com
Mon Jul 13 08:43:05 CEST 2026
FIT cipher support currently allocates the output buffer inside the AES
helper. SPL often needs to decrypt directly into a caller-selected
buffer, for example a load buffer or a scratch buffer used before
decompression.
Add a decrypt_to callback to the FIT cipher algorithm and wire it up for
AES. The existing allocating decrypt path becomes a wrapper around the
new helper.
Validate the FIT cipher key length, IV length and unciphered-size
property while preparing decryption, and build lib/aes/ by phase when
FIT_CIPHER is enabled so the target-side decrypt helper is available to
SPL builds. Use the DM AES provider helper when enabled, retaining the
software implementation only when no provider supports the operation.
For U-Boot proper, use decrypt_to for in-place decryption when the FIT
payload is already in writable RAM. The encrypted data is no longer
needed after hash verification, and this avoids a full-size allocation
for encrypted payloads loaded into DRAM.
Add sandbox coverage for out-of-place and in-place AES-256 decrypt and
malformed key, IV and size inputs.
Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
---
Changes v3 -> v4:
- Validate cipher metadata before reading the key length
- Preserve hard provider failures and fall back only when unsupported
- Treat -EINVAL as a hard provider error
- Fix disabled-feature declarations and use the public test prototype
- Add in-place decrypt and malformed-input tests
- Simplify the legacy allocating decrypt wrapper
Changes v2 -> v3:
- Flip the image_aes_decrypt_to() host-tool guard (suggested by Simon Glass)
- Let image_aes_decrypt_to() be the single length-validation path
(suggested by Simon Glass)
- Document that AES CBC decrypt providers must support in-place decrypt
(suggested by Simon Glass)
Changes v1 -> v2:
- Explain FIT cipher validation (suggested by Simon Glass)
- Explain phase-keyed lib/aes builds (suggested by Simon Glass)
- Return -ENOSYS without decrypt support (suggested by Simon Glass)
- Use decrypt_to for U-Boot proper in-place decrypt
---
boot/image-cipher.c | 45 ++++++++++++++++++----
boot/image-fit.c | 33 ++++++++++++++--
include/image.h | 39 +++++++++++++++++--
include/u-boot/aes.h | 27 ++++++++++----
lib/Makefile | 2 +-
lib/aes/aes-decrypt.c | 91 +++++++++++++++++++++++++++++++++++++--------
test/lib/Makefile | 3 ++
test/lib/test_aes_decrypt.c | 89 ++++++++++++++++++++++++++++++++++++++++++++
8 files changed, 290 insertions(+), 39 deletions(-)
diff --git a/boot/image-cipher.c b/boot/image-cipher.c
index 9d389f26cea..9470370a534 100644
--- a/boot/image-cipher.c
+++ b/boot/image-cipher.c
@@ -25,6 +25,7 @@ struct cipher_algo cipher_algos[] = {
#endif
.encrypt = image_aes_encrypt,
.decrypt = image_aes_decrypt,
+ .decrypt_to = image_aes_decrypt_to,
.add_cipher_data = image_aes_add_cipher_data
},
{
@@ -36,6 +37,7 @@ struct cipher_algo cipher_algos[] = {
#endif
.encrypt = image_aes_encrypt,
.decrypt = image_aes_decrypt,
+ .decrypt_to = image_aes_decrypt_to,
.add_cipher_data = image_aes_add_cipher_data
},
{
@@ -47,6 +49,7 @@ struct cipher_algo cipher_algos[] = {
#endif
.encrypt = image_aes_encrypt,
.decrypt = image_aes_decrypt,
+ .decrypt_to = image_aes_decrypt_to,
.add_cipher_data = image_aes_add_cipher_data
}
};
@@ -70,6 +73,7 @@ static int fit_image_setup_decrypt(struct image_cipher_info *info,
int cipher_noffset)
{
const void *fdt = gd_fdt_blob();
+ int key_len, iv_len;
const char *node_name;
char node_path[128];
int noffset;
@@ -94,7 +98,7 @@ static int fit_image_setup_decrypt(struct image_cipher_info *info,
return -1;
}
- info->iv = fdt_getprop(fit, cipher_noffset, "iv", NULL);
+ info->iv = fdt_getprop(fit, cipher_noffset, "iv", &iv_len);
info->ivname = fdt_getprop(fit, cipher_noffset, "iv-name-hint", NULL);
if (!info->iv && !info->ivname) {
@@ -136,20 +140,28 @@ static int fit_image_setup_decrypt(struct image_cipher_info *info,
}
/* read key */
- info->key = fdt_getprop(fdt, noffset, "key", NULL);
+ info->key = fdt_getprop(fdt, noffset, "key", &key_len);
if (!info->key) {
printf("Can't get key in cipher node '%s'\n", node_path);
return -1;
}
+ if (key_len != info->cipher->key_len) {
+ printf("Bad key length in cipher node '%s'\n", node_path);
+ return -1;
+ }
/* read iv */
if (!info->iv) {
- info->iv = fdt_getprop(fdt, noffset, "iv", NULL);
+ info->iv = fdt_getprop(fdt, noffset, "iv", &iv_len);
if (!info->iv) {
printf("Can't get IV in cipher node '%s'\n", node_path);
return -1;
}
}
+ if (iv_len != info->cipher->iv_len) {
+ printf("Bad IV length for cipher in image '%s'\n", node_name);
+ return -1;
+ }
return 0;
}
@@ -165,11 +177,28 @@ int fit_image_decrypt_data(const void *fit,
ret = fit_image_setup_decrypt(&info, fit, image_noffset,
cipher_noffset);
if (ret < 0)
- goto out;
+ return ret;
+
+ return info.cipher->decrypt(&info, data_ciphered, size_ciphered,
+ data_unciphered, size_unciphered);
+}
+
+int fit_image_decrypt_data_to(const void *fit,
+ int image_noffset, int cipher_noffset,
+ const void *data_ciphered, size_t size_ciphered,
+ void *data_unciphered, size_t *size_unciphered)
+{
+ struct image_cipher_info info;
+ int ret;
+
+ ret = fit_image_setup_decrypt(&info, fit, image_noffset,
+ cipher_noffset);
+ if (ret < 0)
+ return ret;
- ret = info.cipher->decrypt(&info, data_ciphered, size_ciphered,
- data_unciphered, size_unciphered);
+ if (!info.cipher->decrypt_to)
+ return -ENOSYS;
- out:
- return ret;
+ return info.cipher->decrypt_to(&info, data_ciphered, size_ciphered,
+ data_unciphered, size_unciphered);
}
diff --git a/boot/image-fit.c b/boot/image-fit.c
index 9af38ed8d82..6b55316dd37 100644
--- a/boot/image-fit.c
+++ b/boot/image-fit.c
@@ -1028,7 +1028,7 @@ int fit_image_get_data_size(const void *fit, int noffset, int *data_size)
*
* @fit: pointer to the FIT image header
* @noffset: component image node offset
- * @data_size: holds the data-size property
+ * @data_size: holds the data-size-unciphered property
*
* returns:
* 0, on success
@@ -1038,10 +1038,13 @@ int fit_image_get_data_size_unciphered(const void *fit, int noffset,
size_t *data_size)
{
const fdt32_t *val;
+ int len;
- val = fdt_getprop(fit, noffset, "data-size-unciphered", NULL);
+ val = fdt_getprop(fit, noffset, "data-size-unciphered", &len);
if (!val)
return -ENOENT;
+ if (len != sizeof(*val))
+ return -EINVAL;
*data_size = (size_t)fdt32_to_cpu(*val);
@@ -1562,15 +1565,37 @@ static int fit_image_uncipher(const void *fit, int image_noffset,
if (cipher_noffset < 0)
return 0;
+#ifndef USE_HOSTCC
+ if (!tools_build()) {
+ ulong start = map_to_sysmem(*data);
+ ulong end = start + *size;
+
+ /*
+ * Avoid a full-size allocation when the FIT payload is already
+ * in writable DRAM. The encrypted bytes are no longer needed
+ * after hash verification has completed.
+ */
+ if (end >= start && start >= gd->ram_base && end <= gd->ram_top) {
+ ret = fit_image_decrypt_data_to(fit, image_noffset,
+ cipher_noffset,
+ *data, *size, *data,
+ &size_dst);
+ if (ret != -ENOSYS)
+ goto out;
+ }
+ }
+#endif
+
ret = fit_image_decrypt_data(fit, image_noffset, cipher_noffset,
*data, *size, &dst, &size_dst);
if (ret)
goto out;
*data = dst;
- *size = size_dst;
+out:
+ if (!ret)
+ *size = size_dst;
- out:
return ret;
}
diff --git a/include/image.h b/include/image.h
index 9c8a746d576..5edbf8fdc33 100644
--- a/include/image.h
+++ b/include/image.h
@@ -1862,11 +1862,40 @@ int fit_image_check_sig(const void *fit, int noffset, const void *data,
size_t size, const void *key_blob, int required_keynode,
char **err_msgp);
-int fit_image_decrypt_data(const void *fit,
- int image_noffset, int cipher_noffset,
- const void *data, size_t size,
+/**
+ * fit_image_decrypt_data() - Decrypt a FIT image payload
+ *
+ * @fit: FIT image
+ * @image_noffset: Offset of the image node to decrypt
+ * @cipher_noffset: Offset of the cipher node for the image
+ * @data: Encrypted image payload
+ * @size: Size of encrypted image payload
+ * @data_unciphered: Returns allocated decrypted payload
+ * @size_unciphered: Returns size of decrypted payload
+ * Return: 0 on success, <0 on error
+ */
+int fit_image_decrypt_data(const void *fit, int image_noffset,
+ int cipher_noffset, const void *data, size_t size,
void **data_unciphered, size_t *size_unciphered);
+/**
+ * fit_image_decrypt_data_to() - Decrypt a FIT image payload to a buffer
+ *
+ * @fit: FIT image
+ * @image_noffset: Offset of the image node to decrypt
+ * @cipher_noffset: Offset of the cipher node for the image
+ * @data: Encrypted image payload
+ * @size: Size of encrypted image payload
+ * @data_unciphered: Destination buffer for decrypted payload. The caller
+ * must provide at least @size bytes.
+ * @size_unciphered: Returns size of decrypted payload
+ * Return: 0 on success, <0 on error
+ */
+int fit_image_decrypt_data_to(const void *fit,
+ int image_noffset, int cipher_noffset,
+ const void *data, size_t size,
+ void *data_unciphered, size_t *size_unciphered);
+
/**
* fit_region_make_list() - Make a list of regions to hash
*
@@ -1960,6 +1989,10 @@ struct cipher_algo {
int (*decrypt)(struct image_cipher_info *info,
const void *cipher, size_t cipher_len,
void **data, size_t *data_len);
+
+ int (*decrypt_to)(struct image_cipher_info *info,
+ const void *cipher, size_t cipher_len,
+ void *data, size_t *data_len);
};
int fit_image_cipher_get_algo(const void *fit, int noffset, char **algo);
diff --git a/include/u-boot/aes.h b/include/u-boot/aes.h
index acbc50b9e6f..8fd43f02adc 100644
--- a/include/u-boot/aes.h
+++ b/include/u-boot/aes.h
@@ -16,15 +16,16 @@ int image_aes_encrypt(struct image_cipher_info *info,
int image_aes_add_cipher_data(struct image_cipher_info *info, void *keydest,
void *fit, int node_noffset);
#else
-int image_aes_encrypt(struct image_cipher_info *info,
- const unsigned char *data, int size,
- unsigned char **cipher, int *cipher_len)
+static inline int image_aes_encrypt(struct image_cipher_info *info,
+ const unsigned char *data, int size,
+ unsigned char **cipher, int *cipher_len)
{
return -ENXIO;
}
-int image_aes_add_cipher_data(struct image_cipher_info *info, void *keydest,
- void *fit, int node_noffset)
+static inline int image_aes_add_cipher_data(struct image_cipher_info *info,
+ void *keydest, void *fit,
+ int node_noffset)
{
return -ENXIO;
}
@@ -34,10 +35,20 @@ int image_aes_add_cipher_data(struct image_cipher_info *info, void *keydest,
int image_aes_decrypt(struct image_cipher_info *info,
const void *cipher, size_t cipher_len,
void **data, size_t *size);
+int image_aes_decrypt_to(struct image_cipher_info *info,
+ const void *cipher, size_t cipher_len,
+ void *data, size_t *size);
#else
-int image_aes_decrypt(struct image_cipher_info *info,
- const void *cipher, size_t cipher_len,
- void **data, size_t *size)
+static inline int image_aes_decrypt(struct image_cipher_info *info,
+ const void *cipher, size_t cipher_len,
+ void **data, size_t *size)
+{
+ return -ENXIO;
+}
+
+static inline int image_aes_decrypt_to(struct image_cipher_info *info,
+ const void *cipher, size_t cipher_len,
+ void *data, size_t *size)
{
return -ENXIO;
}
diff --git a/lib/Makefile b/lib/Makefile
index d0ffabc2b47..c69a928e6d8 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -19,7 +19,6 @@ obj-$(CONFIG_ARCH_AT91) += at91/
obj-$(CONFIG_OPTEE_LIB) += optee/
obj-$(CONFIG_AES) += aes.o
-obj-$(CONFIG_AES) += aes/
obj-$(CONFIG_$(PHASE_)BINMAN_FDT) += binman.o
obj-$(CONFIG_FW_LOADER) += fw_loader.o
@@ -88,6 +87,7 @@ obj-$(CONFIG_$(PHASE_)ASN1_DECODER_LEGACY) += asn1_decoder.o
obj-$(CONFIG_$(PHASE_)ZLIB) += zlib/
obj-$(CONFIG_$(PHASE_)ZSTD) += zstd/
+obj-$(CONFIG_$(PHASE_)FIT_CIPHER) += aes/
obj-$(CONFIG_$(PHASE_)GZIP) += gunzip.o
obj-$(CONFIG_$(PHASE_)LZO) += lzo/
obj-$(CONFIG_$(PHASE_)LZMA) += lzma/
diff --git a/lib/aes/aes-decrypt.c b/lib/aes/aes-decrypt.c
index 741102a4723..43a5f8742bb 100644
--- a/lib/aes/aes-decrypt.c
+++ b/lib/aes/aes-decrypt.c
@@ -4,37 +4,98 @@
*/
#ifndef USE_HOSTCC
+#include <dm.h>
#include <malloc.h>
#endif
#include <image.h>
#include <uboot_aes.h>
+#ifndef USE_HOSTCC
+static int image_aes_validate(struct image_cipher_info *info,
+ const void *cipher, size_t cipher_len,
+ void *data, size_t *size)
+{
+ if (!info || !info->cipher || !info->key || !info->iv || !cipher ||
+ !data || !size)
+ return -EINVAL;
+ if (info->cipher->iv_len != AES_BLOCK_LENGTH ||
+ (info->cipher->key_len != AES128_KEY_LENGTH &&
+ info->cipher->key_len != AES192_KEY_LENGTH &&
+ info->cipher->key_len != AES256_KEY_LENGTH))
+ return -EINVAL;
+ if (!cipher_len || cipher_len % AES_BLOCK_LENGTH ||
+ info->size_unciphered > cipher_len)
+ return -EINVAL;
+
+ return 0;
+}
+#endif
+
+int image_aes_decrypt_to(struct image_cipher_info *info,
+ const void *cipher, size_t cipher_len,
+ void *data, size_t *size)
+{
+#ifdef USE_HOSTCC
+ return -ENOSYS;
+#else
+ unsigned int aes_blocks, key_len;
+ int ret;
+
+ ret = image_aes_validate(info, cipher, cipher_len, data, size);
+ if (ret)
+ return ret;
+ key_len = info->cipher->key_len;
+ aes_blocks = cipher_len / AES_BLOCK_LENGTH;
+
+ if (CONFIG_IS_ENABLED(DM_AES)) {
+ ret = dm_aes_cbc_decrypt_with_key(key_len * 8, (u8 *)info->key,
+ (u8 *)info->iv, (u8 *)cipher,
+ data, aes_blocks);
+ if (!ret) {
+ *size = info->size_unciphered;
+ return 0;
+ }
+ if (ret != -ENODEV && ret != -EOPNOTSUPP)
+ return ret;
+ }
+
+ if (!IS_ENABLED(CONFIG_XPL_BUILD)) {
+ unsigned char key_exp[AES256_EXPAND_KEY_LENGTH];
+
+ /* First we expand the key. */
+ aes_expand_key((u8 *)info->key, key_len, key_exp);
+
+ aes_cbc_decrypt_blocks(key_len, key_exp, (u8 *)info->iv,
+ (u8 *)cipher, data, aes_blocks);
+ *size = info->size_unciphered;
+ return 0;
+ }
+
+ return -ENOSYS;
+#endif
+}
+
int image_aes_decrypt(struct image_cipher_info *info,
const void *cipher, size_t cipher_len,
void **data, size_t *size)
{
-#ifndef USE_HOSTCC
- unsigned char key_exp[AES256_EXPAND_KEY_LENGTH];
- unsigned int aes_blocks, key_len = info->cipher->key_len;
+#ifdef USE_HOSTCC
+ return 0;
+#else
+ int ret;
*data = malloc(cipher_len);
if (!*data) {
printf("Can't allocate memory to decrypt\n");
return -ENOMEM;
}
- *size = info->size_unciphered;
-
- memcpy(&key_exp[0], info->key, key_len);
-
- /* First we expand the key. */
- aes_expand_key((u8 *)info->key, key_len, key_exp);
- /* Calculate the number of AES blocks to encrypt. */
- aes_blocks = DIV_ROUND_UP(cipher_len, AES_BLOCK_LENGTH);
+ ret = image_aes_decrypt_to(info, cipher, cipher_len, *data, size);
+ if (ret) {
+ free(*data);
+ *data = NULL;
+ }
- aes_cbc_decrypt_blocks(key_len, key_exp, (u8 *)info->iv,
- (u8 *)cipher, *data, aes_blocks);
+ return ret;
#endif
-
- return 0;
}
diff --git a/test/lib/Makefile b/test/lib/Makefile
index f25383a40e5..721d1470185 100644
--- a/test/lib/Makefile
+++ b/test/lib/Makefile
@@ -29,6 +29,9 @@ obj-$(CONFIG_ERRNO_STR) += test_errno_str.o
obj-$(CONFIG_UT_LIB_ASN1) += asn1.o
obj-$(CONFIG_UT_LIB_RSA) += rsa.o
obj-$(CONFIG_AES) += test_aes.o
+ifeq ($(CONFIG_FIT_CIPHER)$(CONFIG_DM_AES),yy)
+obj-y += test_aes_decrypt.o
+endif
obj-$(CONFIG_SHA256) += test_sha256_hmac.o
obj-$(CONFIG_HKDF_MBEDTLS) += test_sha256_hkdf.o
obj-$(CONFIG_GETOPT) += getopt.o
diff --git a/test/lib/test_aes_decrypt.c b/test/lib/test_aes_decrypt.c
new file mode 100644
index 00000000000..3b498e23e4b
--- /dev/null
+++ b/test/lib/test_aes_decrypt.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Tests for target-side FIT AES decryption
+ *
+ * Copyright (C) 2026 James Hilliard
+ */
+
+#include <image.h>
+#include <u-boot/aes.h>
+#include <uboot_aes.h>
+#include <test/lib.h>
+#include <test/test.h>
+#include <test/ut.h>
+
+static int lib_test_image_aes_decrypt(struct unit_test_state *uts)
+{
+ u8 key[AES256_KEY_LENGTH] = { };
+ u8 key_exp[AES256_EXPAND_KEY_LENGTH];
+ u8 iv[AES_BLOCK_LENGTH] = { };
+ u8 plain[2 * AES_BLOCK_LENGTH];
+ u8 cipher[sizeof(plain)];
+ u8 output[sizeof(plain)];
+ struct cipher_algo algo = {
+ .name = "aes256",
+ .key_len = sizeof(key),
+ .iv_len = sizeof(iv),
+ };
+ struct image_cipher_info info = {
+ .cipher = &algo,
+ .key = key,
+ .iv = iv,
+ .size_unciphered = sizeof(plain),
+ };
+ size_t size;
+ int i, ret;
+
+ for (i = 0; i < sizeof(key); i++)
+ key[i] = i;
+ for (i = 0; i < sizeof(iv); i++)
+ iv[i] = 0x80 + i;
+ for (i = 0; i < sizeof(plain); i++)
+ plain[i] = 0x40 + i;
+
+ aes_expand_key(key, sizeof(key), key_exp);
+ aes_cbc_encrypt_blocks(sizeof(key), key_exp, iv, plain, cipher,
+ ARRAY_SIZE(cipher) / AES_BLOCK_LENGTH);
+
+ size = 0;
+ ut_assertok(image_aes_decrypt_to(&info, cipher, sizeof(cipher), output,
+ &size));
+ ut_asserteq(sizeof(plain), size);
+ ut_asserteq_mem(plain, output, sizeof(plain));
+
+ memcpy(output, cipher, sizeof(cipher));
+ size = 0;
+ ut_assertok(image_aes_decrypt_to(&info, output, sizeof(output), output,
+ &size));
+ ut_asserteq(sizeof(plain), size);
+ ut_asserteq_mem(plain, output, sizeof(plain));
+
+ size = 0x55;
+ ret = image_aes_decrypt_to(&info, cipher, sizeof(cipher) - 1, output,
+ &size);
+ ut_asserteq(-EINVAL, ret);
+ ut_asserteq(0x55, size);
+
+ info.size_unciphered = sizeof(cipher) + 1;
+ ret = image_aes_decrypt_to(&info, cipher, sizeof(cipher), output, &size);
+ ut_asserteq(-EINVAL, ret);
+ info.size_unciphered = sizeof(plain);
+
+ info.key = NULL;
+ ret = image_aes_decrypt_to(&info, cipher, sizeof(cipher), output, &size);
+ ut_asserteq(-EINVAL, ret);
+ info.key = key;
+ info.iv = NULL;
+ ret = image_aes_decrypt_to(&info, cipher, sizeof(cipher), output, &size);
+ ut_asserteq(-EINVAL, ret);
+ info.iv = iv;
+ info.cipher = NULL;
+ ret = image_aes_decrypt_to(&info, cipher, sizeof(cipher), output, &size);
+ ut_asserteq(-EINVAL, ret);
+ ret = image_aes_decrypt_to(NULL, cipher, sizeof(cipher), output, &size);
+ ut_asserteq(-EINVAL, ret);
+
+ return 0;
+}
+
+LIB_TEST(lib_test_image_aes_decrypt, 0);
--
2.53.0
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