arch/x86: add functions to generate random numbers

Using x86 RDRAND instruction, two functions are supplied to
generate a 32bit or 64bit number.

One potential usage is the sealing key generation for SGX.

BUG=chrome-os-partner:62438
BRANCH=NONE
TEST=Tested on Eve to generate a 64bit random number.

Change-Id: I50cbeda4de17ccf2fc5efc1fe04f6b1a31ec268c
Signed-off-by: Robbie Zhang <robbie.zhang@intel.com>
Reviewed-on: https://review.coreboot.org/18362
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

2 files changed, 84 insertions, 0 deletions

diff --git a/src/arch/x86/Makefile.inc b/src/arch/x86/Makefile.inc
index c4bb1cccef..332e8ec6f6 100644
--- a/src/arch/x86/Makefile.inc
+++ b/src/arch/x86/Makefile.inc
@@ -334,6 +334,7 @@ ramstage-$(CONFIG_GENERATE_MP_TABLE) += mpspec.c
 ramstage-y += pci_ops_conf1.c
 ramstage-$(CONFIG_MMCONF_SUPPORT) += pci_ops_mmconf.c
 ramstage-$(CONFIG_GENERATE_PIRQ_TABLE) += pirq_routing.c
+ramstage-y += rdrand.c
 ramstage-$(CONFIG_GENERATE_SMBIOS_TABLES) += smbios.c
 ramstage-y += tables.c
 ramstage-$(CONFIG_COOP_MULTITASKING) += thread.c
diff --git a/src/arch/x86/rdrand.c b/src/arch/x86/rdrand.c
new file mode 100644
index 0000000000..dc7ed60a61
--- /dev/null
+++ b/src/arch/x86/rdrand.c
@@ -0,0 +1,83 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2017 Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * 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 <random.h>
+#include <rules.h>
+
+/*
+ * Intel recommends that applications attempt 10 retries in a tight loop
+ * in the unlikely event that the RDRAND instruction does not successfully
+ * return a random number. The odds of ten failures in a row would in fact
+ * be an indication of a larger CPU issue.
+ */
+#define RDRAND_RETRY_LOOPS 10
+
+/*
+ * Generate a 32-bit random number through RDRAND instruction.
+ * Carry flag is set on RDRAND success and 0 on failure.
+ */
+static inline uint8_t rdrand_32(uint32_t *rand)
+{
+	uint8_t carry;
+
+	__asm__ __volatile__(
+	     ".byte 0x0f; .byte 0xc7; .byte 0xf0; setc %1"
+	     : "=a" (*rand), "=qm" (carry));
+	return carry;
+}
+
+/*
+ * Generate a 64-bit random number through RDRAND instruction.
+ * Carry flag is set on RDRAND success and 0 on failure.
+ */
+static inline uint8_t rdrand_64(uint64_t *rand)
+{
+	uint8_t carry;
+
+	__asm__ __volatile__(
+	     ".byte 0x48; .byte 0x0f; .byte 0xc7; .byte 0xf0; setc %1"
+	     : "=a" (*rand), "=qm" (carry));
+	return carry;
+}
+
+int get_random_number_32(uint32_t *rand)
+{
+	int i;
+
+	/* Perform a loop call until RDRAND succeeds or returns failure. */
+	for (i = 0; i < RDRAND_RETRY_LOOPS; i++) {
+		if (rdrand_32(rand))
+			return 0;
+	}
+	return -1;
+}
+
+int get_random_number_64(uint64_t *rand)
+{
+	int i;
+	uint32_t rand_high, rand_low;
+
+	/* Perform a loop call until RDRAND succeeds or returns failure. */
+	for (i = 0; i < RDRAND_RETRY_LOOPS; i++) {
+		if (ENV_X86_64 && rdrand_64(rand))
+			return 0;
+		else if (rdrand_32(&rand_high) && rdrand_32(&rand_low)) {
+			*rand = ((uint64_t)rand_high << 32) |
+				(uint64_t)rand_low;
+			return 0;
+		}
+	}
+	return -1;
+}