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Subject[PATCH] arm64: add support for rng-seed
Date
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 +++++++++
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.
+
+/ {
+ 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);
+
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
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