[PATCH v3 2/5] fdt: kaslr seed from RNG device

seanedmond
2023-09-12T21:35:21Z

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

Add support for KASLR seed from the RNG device. Invokes dm_rng_read()
API to read 8-bytes of random bytes. Performs the FDT fixup using event
spy. To enable use CONFIG_KASLR_RNG_SEED

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>
---
common/fdt_support.c | 36 ++++++++++++++++++++++++++++++++++++
lib/Kconfig | 7 +++++++
2 files changed, 43 insertions(+)

diff --git a/common/fdt_support.c b/common/fdt_support.c
index 52be4375b4..09ce582865 100644
--- a/common/fdt_support.c
+++ b/common/fdt_support.c
@@ -12,7 +12,10 @@
#include <log.h>
#include <mapmem.h>
#include <net.h>
+#include <rng.h>
#include <stdio_dev.h>
+#include <dm/device.h>
+#include <dm/uclass.h>
#include <dm/ofnode.h>
#include <linux/ctype.h>
#include <linux/types.h>
@@ -650,6 +653,39 @@ int fdt_fixup_kaslr_seed(ofnode node, const u8 *seed, int len)
return 0;
}

+int fdt_rng_kaslr_seed(void *ctx, struct event *event)
+{
+ u8 rand[8] = {0};
+ struct udevice *dev;
+ int ret;
+ oftree tree = event->data.ft_fixup.tree;
+ ofnode root_node = oftree_root(tree);
+
+ ret = uclass_first_device_err(UCLASS_RNG, &dev);
+ if (ret) {
+ printf("ERROR: Failed to find RNG device\n");
+ return ret;
+ }
+
+ ret = dm_rng_read(dev, rand, sizeof(rand));
+ if (ret) {
+ printf("ERROR: RNG read failed, ret=%d\n", ret);
+ return ret;
+ }
+
+ ret = fdt_fixup_kaslr_seed(root_node, rand, sizeof(rand));
+ if (ret) {
+ printf("ERROR: failed to add kaslr-seed to fdt\n");
+ return ret;
+ }
+
+ return 0;
+}
+
+#if defined(CONFIG_KASLR_RNG_SEED)
+EVENT_SPY(EVT_FT_FIXUP, fdt_rng_kaslr_seed);
+#endif
+
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/lib/Kconfig b/lib/Kconfig
index 3926652db6..545a14343e 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -465,6 +465,13 @@ config VPL_TPM
for the low-level TPM interface, but only one TPM is supported at
a time by the TPM library.

+config KASLR_RNG_SEED
+ bool "Use RNG driver for KASLR random seed"
+ depends on DM_RNG
+ help
+ This enables support for using the RNG driver as entropy source for
+ KASLR seed populated in kernel's device tree.
+
endmenu

menu "Android Verified Boot"
--
2.40.0