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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2016-11-12 21:32:31 +0000
committerIngo Molnar <mingo@kernel.org>2016-11-13 08:23:14 +0100
commit636259880a7e7d3446a707dddebc799da94bdd0b (patch)
tree6ae9f5404dd55746138bbcf0b4c790bd285f3077
parentf135a176426fc643caf6480e3200f1733f58dbf6 (diff)
efi: Add support for seeding the RNG from a UEFI config table
Specify a Linux specific UEFI configuration table that carries some random bits, and use the contents during early boot to seed the kernel's random number generator. This allows much strong random numbers to be generated early on. The entropy is fed to the kernel using add_device_randomness(), which is documented as being appropriate for being called very early. Since UEFI configuration tables may also be consumed by kexec'd kernels, register a reboot notifier that updates the seed in the table. Note that the config table could be generated by the EFI stub or by any other UEFI driver or application (e.g., GRUB), but the random seed table GUID and the associated functionality should be considered an internal kernel interface (unless it is promoted to ABI later on) Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20161112213237.8804-4-matt@codeblueprint.co.uk Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--drivers/firmware/efi/efi.c72
-rw-r--r--include/linux/efi.h8
2 files changed, 80 insertions, 0 deletions
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index a4944e2..9291480 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -23,7 +23,10 @@
#include <linux/of.h>
#include <linux/of_fdt.h>
#include <linux/io.h>
+#include <linux/kexec.h>
#include <linux/platform_device.h>
+#include <linux/random.h>
+#include <linux/reboot.h>
#include <linux/slab.h>
#include <linux/acpi.h>
#include <linux/ucs2_string.h>
@@ -48,6 +51,7 @@ struct efi __read_mostly efi = {
.esrt = EFI_INVALID_TABLE_ADDR,
.properties_table = EFI_INVALID_TABLE_ADDR,
.mem_attr_table = EFI_INVALID_TABLE_ADDR,
+ .rng_seed = EFI_INVALID_TABLE_ADDR,
};
EXPORT_SYMBOL(efi);
@@ -440,6 +444,7 @@ static __initdata efi_config_table_type_t common_tables[] = {
{EFI_SYSTEM_RESOURCE_TABLE_GUID, "ESRT", &efi.esrt},
{EFI_PROPERTIES_TABLE_GUID, "PROP", &efi.properties_table},
{EFI_MEMORY_ATTRIBUTES_TABLE_GUID, "MEMATTR", &efi.mem_attr_table},
+ {LINUX_EFI_RANDOM_SEED_TABLE_GUID, "RNG", &efi.rng_seed},
{NULL_GUID, NULL, NULL},
};
@@ -501,6 +506,29 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
pr_cont("\n");
set_bit(EFI_CONFIG_TABLES, &efi.flags);
+ if (efi.rng_seed != EFI_INVALID_TABLE_ADDR) {
+ struct linux_efi_random_seed *seed;
+ u32 size = 0;
+
+ seed = early_memremap(efi.rng_seed, sizeof(*seed));
+ if (seed != NULL) {
+ size = seed->size;
+ early_memunmap(seed, sizeof(*seed));
+ } else {
+ pr_err("Could not map UEFI random seed!\n");
+ }
+ if (size > 0) {
+ seed = early_memremap(efi.rng_seed,
+ sizeof(*seed) + size);
+ if (seed != NULL) {
+ add_device_randomness(seed->bits, seed->size);
+ early_memunmap(seed, sizeof(*seed) + size);
+ } else {
+ pr_err("Could not map UEFI random seed!\n");
+ }
+ }
+ }
+
/* Parse the EFI Properties table if it exists */
if (efi.properties_table != EFI_INVALID_TABLE_ADDR) {
efi_properties_table_t *tbl;
@@ -824,3 +852,47 @@ int efi_status_to_err(efi_status_t status)
return err;
}
+
+#ifdef CONFIG_KEXEC
+static int update_efi_random_seed(struct notifier_block *nb,
+ unsigned long code, void *unused)
+{
+ struct linux_efi_random_seed *seed;
+ u32 size = 0;
+
+ if (!kexec_in_progress)
+ return NOTIFY_DONE;
+
+ seed = memremap(efi.rng_seed, sizeof(*seed), MEMREMAP_WB);
+ if (seed != NULL) {
+ size = min(seed->size, 32U);
+ memunmap(seed);
+ } else {
+ pr_err("Could not map UEFI random seed!\n");
+ }
+ if (size > 0) {
+ seed = memremap(efi.rng_seed, sizeof(*seed) + size,
+ MEMREMAP_WB);
+ if (seed != NULL) {
+ seed->size = size;
+ get_random_bytes(seed->bits, seed->size);
+ memunmap(seed);
+ } else {
+ pr_err("Could not map UEFI random seed!\n");
+ }
+ }
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block efi_random_seed_nb = {
+ .notifier_call = update_efi_random_seed,
+};
+
+static int register_update_efi_random_seed(void)
+{
+ if (efi.rng_seed == EFI_INVALID_TABLE_ADDR)
+ return 0;
+ return register_reboot_notifier(&efi_random_seed_nb);
+}
+late_initcall(register_update_efi_random_seed);
+#endif
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 2d08948..85e28b1 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -599,6 +599,7 @@ void efi_native_runtime_setup(void);
*/
#define LINUX_EFI_ARM_SCREEN_INFO_TABLE_GUID EFI_GUID(0xe03fc20a, 0x85dc, 0x406e, 0xb9, 0x0e, 0x4a, 0xb5, 0x02, 0x37, 0x1d, 0x95)
#define LINUX_EFI_LOADER_ENTRY_GUID EFI_GUID(0x4a67b082, 0x0a4c, 0x41cf, 0xb6, 0xc7, 0x44, 0x0b, 0x29, 0xbb, 0x8c, 0x4f)
+#define LINUX_EFI_RANDOM_SEED_TABLE_GUID EFI_GUID(0x1ce1e5bc, 0x7ceb, 0x42f2, 0x81, 0xe5, 0x8a, 0xad, 0xf1, 0x80, 0xf5, 0x7b)
typedef struct {
efi_guid_t guid;
@@ -872,6 +873,7 @@ extern struct efi {
unsigned long esrt; /* ESRT table */
unsigned long properties_table; /* properties table */
unsigned long mem_attr_table; /* memory attributes table */
+ unsigned long rng_seed; /* UEFI firmware random seed */
efi_get_time_t *get_time;
efi_set_time_t *set_time;
efi_get_wakeup_time_t *get_wakeup_time;
@@ -1493,4 +1495,10 @@ efi_status_t efi_exit_boot_services(efi_system_table_t *sys_table,
struct efi_boot_memmap *map,
void *priv,
efi_exit_boot_map_processing priv_func);
+
+struct linux_efi_random_seed {
+ u32 size;
+ u8 bits[];
+};
+
#endif /* _LINUX_EFI_H */