[RFC/PATCH 1/3] of: Add early randomness hooks

Laura Abbott
2014-02-12T01:33:23Z

Until randomness is added to the kernel's pools, random
numbers returned may not be truly 'random'. Randomness comes
from a variety of sources in the kernel but much of the
randomness comes from device related initialization. This
means that any random numbers that are needed before drivers
are initialized (e.g. stack canary) may not be truely random.
Fix this by build a list of functions that can be used to add
randomness to the kernel's pools very early. The functions are
tied to particular compatible strings of devicetree nodes. The
flattened devicetree is scanned and if the node is present the
function is called. Note that this must happen on the flattened
devicetree to ensure the randomness gets added to the pool
early enough to make a difference.

Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
---
drivers/of/Kconfig | 7 ++++++
drivers/of/Makefile | 1 +
drivers/of/fdt.c | 7 ++++++
drivers/of/of_randomness.c | 43 +++++++++++++++++++++++++++++++++++++
include/asm-generic/vmlinux.lds.h | 5 ++++
include/linux/of_randomness.h | 42 ++++++++++++++++++++++++++++++++++++
6 files changed, 105 insertions(+), 0 deletions(-)
create mode 100644 drivers/of/of_randomness.c
create mode 100644 include/linux/of_randomness.h

diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index c6973f1..6ae4a38 100644
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -75,4 +75,11 @@ config OF_MTD
depends on MTD
def_bool y

+config OF_RANDOMNESS
+ def_bool n
+ depends on OF_FLATTREE && ARCH_WANT_OF_RANDOMNESS
+ help
+ OpenFirmware hooks to scan for device randomness
+ via flat devicetree
+
endmenu # OF
diff --git a/drivers/of/Makefile b/drivers/of/Makefile
index efd0510..0ce02d1 100644
--- a/drivers/of/Makefile
+++ b/drivers/of/Makefile
@@ -9,3 +9,4 @@ obj-$(CONFIG_OF_MDIO) += of_mdio.o
obj-$(CONFIG_OF_PCI) += of_pci.o
obj-$(CONFIG_OF_PCI_IRQ) += of_pci_irq.o
obj-$(CONFIG_OF_MTD) += of_mtd.o
+obj-$(CONFIG_OF_RANDOMNESS) += of_randomness.o
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 758b4f8..c25960e 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -15,6 +15,7 @@
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_fdt.h>
+#include <linux/of_randomness.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/slab.h>
@@ -889,6 +890,12 @@ bool __init early_init_dt_scan(void *params)
/* Setup memory, calling early_init_dt_add_memory_arch */
of_scan_flat_dt(early_init_dt_scan_memory, NULL);

+#ifdef CONFIG_OF_RANDOMNESS
+ /* Add device randomness */
+ of_scan_flat_dt(early_init_dt_scan_early_randomness, NULL);
+#endif
+
+
return true;
}

diff --git a/drivers/of/of_randomness.c b/drivers/of/of_randomness.c
new file mode 100644
index 0000000..9d23624
--- /dev/null
+++ b/drivers/of/of_randomness.c
@@ -0,0 +1,43 @@
+/* Copyright (c) 2013-2014, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/random.h>
+#include <linux/string.h>
+#include <linux/of_randomness.h>
+#include <linux/of_fdt.h>
+
+int __init early_init_dt_scan_early_randomness(unsigned long node,
+ const char *uname,
+ int depth, void *data)
+{
+ struct early_random_func *f;
+ void *prop;
+ unsigned long len;
+
+ prop = of_get_flat_dt_prop(node, "compatible", &len);
+
+ if (!prop)
+ return 0;
+
+ for (f = __early_random_funcs_start;
+ f < __early_random_funcs_end;
+ f++) {
+ pr_debug("Check compat %s addr %p against %s\n",
+ f->compat_string, f->add_randomness, (char *)prop);
+ if (strcmp(prop, f->compat_string) == 0)
+ f->add_randomness(node);
+ }
+
+ return 0;
+}
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index bc2121f..e5b8be9 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -645,6 +645,11 @@
*(.security_initcall.init) \
VMLINUX_SYMBOL(__security_initcall_end) = .;

+#define EARLY_RANDOM_FUNCS \
+ VMLINUX_SYMBOL(__early_random_funcs_start) = .; \
+ *(.earlyrandom.init) \
+ VMLINUX_SYMBOL(__early_random_funcs_end) = .;
+
#ifdef CONFIG_BLK_DEV_INITRD
#define INIT_RAM_FS \
. = ALIGN(4); \
diff --git a/include/linux/of_randomness.h b/include/linux/of_randomness.h
new file mode 100644
index 0000000..b8b4532
--- /dev/null
+++ b/include/linux/of_randomness.h
@@ -0,0 +1,42 @@
+/* Copyright (c) 2013-2014, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ */
+#ifndef LINUX_OF_RANDOMNESS_H
+#define LINUX_OF_RANDOMNESS_H
+
+extern int early_init_dt_scan_early_randomness(unsigned long node,
+ const char *uname,
+ int depth, void *data);
+
+#ifdef CONFIG_OF_RANDOMNESS
+
+struct early_random_func {
+ char *compat_string;
+ void (*add_randomness)(unsigned long fdt_node);
+};
+
+extern struct early_random_func __early_random_funcs_start[];
+extern struct early_random_func __early_random_funcs_end[];
+
+#define EARLY_RANDOM_FUNC(c, f) \
+static struct early_random_func __early_rand##f __used \
+ __attribute((__section__(".earlyrandom.init"))) = { \
+ .compat_string = c, \
+ .add_randomness = f\
+ } \
+
+#else
+
+#define EARLY_RANDOM_FUNC(f, e)
+#endif
+
+#endif
--
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