Re: [PATCH] arm64: add support for rng-seed

[Hsin-Yi Wang]

On Fri, May 10, 2019 at 2:14 PM Rasmus Villemoes
<linux@xxxxxxxxxxxxxxxxxx> wrote:

> So, why not just have the bootloader add whatever entropy it has via the
> commandline, which already gets mixed in? That requires no kernel
> changes, and works for all architectures.
>
> If anything, perhaps instead of just adding gobbledygook=abc123, make an
> official command line parameter (there was talk about this at some
> point), and have the kernel overwrite the value with xxx so it's not
> visible in /proc/cmdline.
>
> Rasmus

For some arch, besides commandline, we also need to overwrite bootargs
in fdt, otherwise it's still visible by
/sys/firmware/devicetree/base/chosen/bootargs for example.

Originally planned to land v2 as

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index de893c9616a1..96ea5eba9dd5 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 +1115,15 @@ 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)
+               return 1;
+
+       /* try to clear seed so it won't be found. */
+        fdt_nop_property(initial_boot_params, node, "rng-seed");
+
+        add_device_randomness(rng_seed, l);
+
        /* break now */
        return 1;
 }

(For arm64 RW/RO issue, it will be done in other patch.)

If we add parameter into commandline, I think we probably also need to
do similar changes here since there are fdt related overwrite.