Add fdt_kaslrseed function to add kaslr-seed to chosen node

If RANDOMIZE_BASE is enabled in the Linux kernel instructing it to
randomize the virtual address at which the kernel image is loaded, it
expects entropy to be provided by the bootloader by populating
/chosen/kaslr-seed with a 64-bit value from source of entropy at boot.

Add a fdt_kaslrseed function to accommodate this allowing an existing
node to be overwritten if present. For now use the first rng device
but it would be good to enhance this in the future to allow some sort
of selection or policy in choosing the rng device used.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Michal Simek <michal.simek@amd.com>
Cc: Andy Yan <andy.yan@rock-chips.com>
Cc: Akash Gajjar <gajjar04akash@gmail.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Devarsh Thakkar <devarsht@ti.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>

2 files changed, 54 insertions, 0 deletions

diff --git a/boot/fdt_support.c b/boot/fdt_support.c
index 2bd80a9..b1b2679 100644
--- a/boot/fdt_support.c
+++ b/boot/fdt_support.c
@@ -7,12 +7,15 @@
  */
 
 #include <common.h>
+#include <dm.h>
 #include <abuf.h>
 #include <env.h>
 #include <log.h>
 #include <mapmem.h>
 #include <net.h>
+#include <rng.h>
 #include <stdio_dev.h>
+#include <dm/device_compat.h>
 #include <dm/ofnode.h>
 #include <linux/ctype.h>
 #include <linux/types.h>
@@ -274,6 +277,47 @@ int fdt_initrd(void *fdt, ulong initrd_start, ulong initrd_end)
 	return 0;
 }
 
+int fdt_kaslrseed(void *fdt, bool overwrite)
+{
+	int len, err, nodeoffset;
+	struct udevice *dev;
+	const u64 *orig;
+	u64 data = 0;
+
+	err = fdt_check_header(fdt);
+	if (err < 0)
+		return err;
+
+	/* find or create "/chosen" node. */
+	nodeoffset = fdt_find_or_add_subnode(fdt, 0, "chosen");
+	if (nodeoffset < 0)
+		return nodeoffset;
+
+	/* return without error if we are not overwriting and existing non-zero node */
+	orig = fdt_getprop(fdt, nodeoffset, "kaslr-seed", &len);
+	if (orig && len == sizeof(*orig))
+		data = fdt64_to_cpu(*orig);
+	if (data && !overwrite) {
+		debug("not overwriting existing kaslr-seed\n");
+		return 0;
+	}
+	err = uclass_get_device(UCLASS_RNG, 0, &dev);
+	if (err) {
+		printf("No RNG device\n");
+		return err;
+	}
+	err = dm_rng_read(dev, &data, sizeof(data));
+	if (err) {
+		dev_err(dev, "dm_rng_read failed: %d\n", err);
+		return err;
+	}
+	err = fdt_setprop(fdt, nodeoffset, "kaslr-seed", &data, sizeof(data));
+	if (err < 0)
+		printf("WARNING: could not set kaslr-seed %s.\n", fdt_strerror(err));
+
+	return err;
+}
+
 /**
  * board_fdt_chosen_bootargs - boards may override this function to use
  *                             alternative kernel command line arguments
diff --git a/include/fdt_support.h b/include/fdt_support.h
index 4b71b89..741e236 100644
--- a/include/fdt_support.h
+++ b/include/fdt_support.h
@@ -463,4 +463,14 @@ void fdt_fixup_board_enet(void *blob);
 #ifdef CONFIG_CMD_PSTORE
 void fdt_fixup_pstore(void *blob);
 #endif
+
+/**
+ * fdt_kaslrseed() - create a 'kaslr-seed' node in chosen
+ *
+ * @blob:	fdt blob
+ * @overwrite:	do not overwrite existing non-zero node unless true
+ * Return:	0 if OK, -ve on error
+ */
+int fdt_kaslrseed(void *blob, bool overwrite);
+
 #endif /* ifndef __FDT_SUPPORT_H */