[PATCH v4 2/3] fdt: add support for rng-seed

Hsin-Yi Wang
2019-05-19T16:04:45Z

Introducing a chosen node, rng-seed, which is an entropy that can be
passed to kernel called very early to increase initial device
randomness. Bootloader should provide this entropy and the value is
read from /chosen/rng-seed in DT.

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
---
change log v2->v4:
* v3 abandoned
* fix doc error
---
Documentation/devicetree/bindings/chosen.txt | 14 ++++++++++++++
drivers/of/fdt.c | 10 ++++++++++
2 files changed, 24 insertions(+)

diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
index 45e79172a646..678e81bc4383 100644
--- a/Documentation/devicetree/bindings/chosen.txt
+++ b/Documentation/devicetree/bindings/chosen.txt
@@ -28,6 +28,20 @@ mode) when EFI_RNG_PROTOCOL is supported, it will be overwritten by
the Linux EFI stub (which will populate the property itself, using
EFI_RNG_PROTOCOL).

+rng-seed
+-----------
+
+This property serves as an entropy to add device randomness. It is parsed
+as a byte array, e.g.
+
+/ {
+ chosen {
+ rng-seed = <0x31 0x95 0x1b 0x3c 0xc9 0xfa 0xb3 ...>;
+ };
+};
+
+This random value should be provided by bootloader.
+
stdout-path
-----------

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index de893c9616a1..7f3d72921b23 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -24,6 +24,7 @@
#include <linux/debugfs.h>
#include <linux/serial_core.h>
#include <linux/sysfs.h>
+#include <linux/random.h>

#include <asm/setup.h> /* for COMMAND_LINE_SIZE */
#include <asm/page.h>
@@ -1079,6 +1080,7 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
{
int l;
const char *p;
+ const void *rng_seed;

pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname);

@@ -1113,6 +1115,14 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,

pr_debug("Command line is: %s\n", (char*)data);

+ rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l);
+ if (rng_seed && l > 0) {
+ add_device_randomness(rng_seed, l);
+
+ /* try to clear seed so it won't be found. */
+ fdt_delprop(initial_boot_params, node, "rng-seed");
+ }
+
/* break now */
return 1;
}
--
2.20.1