[PATCH 2/4] fdt: kaslr seed from tpm entropy

seanedmond
2023-08-29T20:32:58Z

From: Dhananjay Phadke <dphadke@linux.microsoft.com>

Add support for KASLR seed from TPM device. Invokes tpm_get_random()
API to read 8-bytes of random bytes for KASLR.

Signed-off-by: Dhananjay Phadke <dphadke@linux.microsoft.com>
Signed-off-by: Drew Kluemke <ankluemk@microsoft.com>
Signed-off-by: Sean Edmond <seanedmond@microsoft.com>
---
boot/image-fdt.c | 15 +++++++++++++++
common/fdt_support.c | 30 ++++++++++++++++++++++++++++++
include/fdt_support.h | 8 ++++++++
lib/Kconfig | 9 +++++++++
4 files changed, 62 insertions(+)

diff --git a/boot/image-fdt.c b/boot/image-fdt.c
index f10200f647..ed38ed77b9 100644
--- a/boot/image-fdt.c
+++ b/boot/image-fdt.c
@@ -624,6 +624,21 @@ int image_setup_libfdt(struct bootm_headers *images, void *blob,
goto err;
}

+ if (IS_ENABLED(CONFIG_KASLR_TPM_SEED)) {
+ ofnode root;
+
+ ret = root_ofnode_from_fdt(blob, &root);
+ if (ret) {
+ printf("ERROR: Unable to get root ofnode\n");
+ goto err;
+ }
+ ret = fdt_tpm_kaslr_seed(root);
+ if (ret) {
+ printf("ERROR: fdt fixup KASLR failed: %d\n", ret);
+ goto err;
+ }
+ }
+
fdt_ret = optee_copy_fdt_nodes(blob);
if (fdt_ret) {
printf("ERROR: transfer of optee nodes to new fdt failed: %s\n",
diff --git a/common/fdt_support.c b/common/fdt_support.c
index 52be4375b4..d338fcde54 100644
--- a/common/fdt_support.c
+++ b/common/fdt_support.c
@@ -13,6 +13,9 @@
#include <mapmem.h>
#include <net.h>
#include <stdio_dev.h>
+#include <tpm_api.h>
+#include <dm/device.h>
+#include <dm/uclass.h>
#include <dm/ofnode.h>
#include <linux/ctype.h>
#include <linux/types.h>
@@ -650,6 +653,33 @@ int fdt_fixup_kaslr_seed(ofnode node, const u8 *seed, int len)
return 0;
}

+int fdt_tpm_kaslr_seed(ofnode node)
+{
+ u8 rand[8] = {0};
+ struct udevice *dev;
+ int ret;
+
+ ret = uclass_first_device_err(UCLASS_TPM, &dev);
+ if (ret) {
+ printf("ERROR: Failed to find TPM device\n");
+ return ret;
+ }
+
+ ret = tpm_get_random(dev, rand, sizeof(rand));
+ if (ret) {
+ printf("ERROR: TPM GetRandom failed, ret=%d\n", ret);
+ return ret;
+ }
+
+ ret = fdt_fixup_kaslr_seed(node, rand, sizeof(rand));
+ if (ret) {
+ printf("ERROR: failed to add kaslr-seed to fdt\n");
+ return ret;
+ }
+
+ return 0;
+}
+
int fdt_record_loadable(void *blob, u32 index, const char *name,
uintptr_t load_addr, u32 size, uintptr_t entry_point,
const char *type, const char *os, const char *arch)
diff --git a/include/fdt_support.h b/include/fdt_support.h
index d967118bed..117ca14ca5 100644
--- a/include/fdt_support.h
+++ b/include/fdt_support.h
@@ -130,6 +130,14 @@ void fdt_fixup_ethernet(void *fdt);
*/
int fdt_fixup_kaslr_seed(ofnode node, const u8 *seed, int len);

+/*
+ * fdt_add_tpm_kaslr_seed - Add kalsr-seed node in Device tree with random
+ * bytes from TPM device
+ * @node: ofnode
+ * @eret: 0 for success
+ */
+int fdt_tpm_kaslr_seed(ofnode node);
+
int fdt_find_and_setprop(void *fdt, const char *node, const char *prop,
const void *val, int len, int create);
void fdt_fixup_qe_firmware(void *fdt);
diff --git a/lib/Kconfig b/lib/Kconfig
index 3926652db6..1530ef7c86 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -465,6 +465,15 @@ config VPL_TPM
for the low-level TPM interface, but only one TPM is supported at
a time by the TPM library.

+config KASLR_TPM_SEED
+ bool "Use TPM for KASLR random seed"
+ depends on TPM_V1 || TPM_V2
+ help
+ This enables support for using TPMs as entropy source for KASLR seed
+ populated in kernel's device tree. Both TPMv1 and TPMv2 are supported
+ for the low-level TPM interface, but only one TPM is supported at
+ a time by the library.
+
endmenu

menu "Android Verified Boot"
--
2.40.0