Re: [PATCH v9 2/3] fdt: add support for rng-seed

[Hsin-Yi Wang]

On Thu, Aug 29, 2019 at 1:36 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> Can this please be a boot param (with the default controlled by the
> CONFIG)? See how CONFIG_RANDOM_TRUST_CPU is wired up...
>
> -Kees
>

Currently rng-seed read and added in setup_arch() -->
setup_machine_fdt().. -> early_init_dt_scan_chosen(), which is earlier
than parse_early_param() that initializes early_param.

If we want to set it as a boot param, add_bootloader_randomness() can
only be called after parse_early_param(). The seed can't be directly
added to pool after it's read in. We need to store into global
variable and load it later.
If this seems okay then I'll add a patch for this. Thanks

--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -1096,13 +1096,15 @@ static const char *config_cmdline = CONFIG_CMDLINE;

+const void* rng_seed;
+int rng_seed_len;
+
 int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
                                                            int depth,
void *data)
 {
        int l = 0;
        const char *p = NULL;
        char *cmdline = data;
-       const void *rng_seed;

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

@@ -1137,10 +1139,8 @@ 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_bootloader_randomness(rng_seed, l);  //
Originally it's added to entropy pool here
-
+       rng_seed = of_get_flat_dt_prop(node, "rng-seed", &rng_seed_len);
+       if (rng_seed && rng_seed_len > 0) {
                /* try to clear seed so it won't be found. */

diff --git a/include/linux/random.h b/include/linux/random.h
index 831a002a1882..946840bba7c1 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -31,6 +31,15 @@ static inline void add_latent_entropy(void)
 static inline void add_latent_entropy(void) {}
 #endif

+extern const void* rng_seed;
+extern int rng_seed_len;
+
+static inline void add_bootloader_entropy(void)
+{
+        if (rng_seed && rng_seed_len > 0)
+                add_bootloader_randomness(rng_seed, rng_seed_len);
+}
+
 extern void add_input_randomness(unsigned int type, unsigned int code,
  unsigned int value) __latent_entropy;
 extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy;
diff --git a/init/main.c b/init/main.c
index 71847af32e4e..f74a8c7b34af 100644
--- a/init/main.c
+++ b/init/main.c
@@ -645,6 +645,7 @@ asmlinkage __visible void __init start_kernel(void)
  * - adding command line entropy
  */
  rand_initialize();
+ add_bootloader_entropy();
  add_latent_entropy();
  add_device_randomness(command_line, strlen(command_line));
  boot_init_stack_canary();