[PATCH v4 2/5] fdt: kaslr seed from RNG device

[seanedmond at linux.microsoft.com]

From: Dhananjay Phadke <dphadke at 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 at linux.microsoft.com>
Signed-off-by: Drew Kluemke <ankluemk at microsoft.com>
Signed-off-by: Sean Edmond <seanedmond at microsoft.com>
---
 boot/fdt_support.c | 36 ++++++++++++++++++++++++++++++++++++
 lib/Kconfig        |  7 +++++++
 2 files changed, 43 insertions(+)

diff --git a/boot/fdt_support.c b/boot/fdt_support.c
index 52be4375b46..09ce5828659 100644
--- a/boot/fdt_support.c
+++ b/boot/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 19649517a39..4f5dfc00d6f 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -477,6 +477,13 @@ 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"
-- 
2.42.0