On Wed, May 8, 2019 at 3:47 AM Rob Herring robh+dt@kernel.org wrote:

+boot-architecture list as there was some discussion about this IIRC.

On Mon, May 6, 2019 at 11:54 PM Hsin-Yi Wang hsinyi@chromium.org wrote:

...

Introducing a chosen node, rng-seed, which is an 64 bytes entropy that can be passed to kernel called very early to increase 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

---

Documentation/devicetree/bindings/chosen.txt | 14 +++++++++

Actually, this file has been converted to json-schema and lives here[1]. I need to remove this one (or leave it with a reference to the new one).

...

arch/arm64/kernel/setup.c | 2 ++ drivers/of/fdt.c | 33 ++++++++++++++++++++ include/linux/of_fdt.h | 1 + 4 files changed, 50 insertions(+)

diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt index 45e79172a646..bfd360691650 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 served as an entropy to add device randomness. It is parsed +as a 64 byte value, e.g.

Why only 64-bytes?

We can also not specify size and read what bootloader can provide.

...

+/ {

•   chosen {
  

•           rng-seed = <0x31951b3c 0xc9fab3a5 0xffdf1660 ...>
  

•   };
  

+};

+This random value should be provided by bootloader.

stdout-path

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c index 413d566405d1..ade4261516dd 100644 --- a/arch/arm64/kernel/setup.c +++ b/arch/arm64/kernel/setup.c @@ -292,6 +292,8 @@ void __init setup_arch(char **cmdline_p) early_fixmap_init(); early_ioremap_init();

•   early_init_dt_rng_seed(__fdt_pointer);
  

I'm trying to reduce or eliminate all these early_init_dt_* calls.

Why is this arch specific and why can't this be done after unflattening? It doesn't look like add_device_randomness() needs anything early.

Currently unflattening is called after setup_machine_fdt(), which called fixmap_remap_fdt() //__fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO), and we can't modify DT after that since it's read only. But we need to clear (eg. write 0 to it) the rng-seed after reading from DT.

...

    setup_machine_fdt(__fdt_pointer);

    parse_early_param();

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c index de893c9616a1..74e2c0c80b91 100644 --- a/drivers/of/fdt.c +++ b/drivers/of/fdt.c @@ -22,6 +22,7 @@ #include <linux/slab.h> #include <linux/libfdt.h> #include <linux/debugfs.h> +#include <linux/random.h> #include <linux/serial_core.h> #include <linux/sysfs.h>

@@ -1117,6 +1118,38 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, return 1; }

+extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,

•                                  pgprot_t prot);
  

+void __init early_init_dt_rng_seed(u64 dt_phys) +{

•   void *fdt;
  

•   int node, size, i;
  

•   fdt64_t *prop;
  

•   u64 rng_seed[8];
  

•   fdt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
  

•   if (!fdt)
  

•           return;
  

•   node = fdt_path_offset(fdt, "/chosen");
  

•   if (node < 0)
  

•           return;
  

•   prop = fdt_getprop_w(fdt, node, "rng-seed", &size);
  

•   if (!prop || size != sizeof(u64) * 8)
  

•           return;
  

•   for (i = 0; i < 8; i++) {
  

•           rng_seed[i] = fdt64_to_cpu(*(prop + i));
  

•           /* clear seed so it won't be found. */
  

•           *(prop + i) = 0;
  

•   }
  

•   add_device_randomness(rng_seed, size);
  

•   return;
  

+}

#ifndef MIN_MEMBLOCK_ADDR #define MIN_MEMBLOCK_ADDR __pa(PAGE_OFFSET) #endif diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h index a713e5d156d8..a4548dd6351e 100644 --- a/include/linux/of_fdt.h +++ b/include/linux/of_fdt.h @@ -71,6 +71,7 @@ extern uint32_t of_get_flat_dt_phandle(unsigned long node);

extern int early_init_dt_scan_chosen(unsigned long node, const char *uname, int depth, void *data); +extern void early_init_dt_rng_seed(u64 dt_phys); extern int early_init_dt_scan_memory(unsigned long node, const char *uname, int depth, void *data); extern int early_init_dt_scan_chosen_stdout(void); -- 2.20.1