plat/qemu: Use RNDR in stack protector
When getting a stack protector canary value, check
if cpu supports FEAT_RNG and use that. Fallback to
old method of using a (hardcoded value ^ timer).
Signed-off-by: Tomas Pilar <tomas@nuviainc.com>
Change-Id: I8181acf8e31661d4cc82bc3a4078f8751909e725
diff --git a/plat/qemu/common/qemu_stack_protector.c b/plat/qemu/common/qemu_stack_protector.c
index c226158..15ce3d6 100644
--- a/plat/qemu/common/qemu_stack_protector.c
+++ b/plat/qemu/common/qemu_stack_protector.c
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2021, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
@@ -7,17 +7,25 @@
#include <stdint.h>
#include <arch_helpers.h>
+#include <arch_features.h>
#include <plat/common/platform.h>
#define RANDOM_CANARY_VALUE ((u_register_t) 3288484550995823360ULL)
u_register_t plat_get_stack_protector_canary(void)
{
+#if ENABLE_FEAT_RNG
+ /* Use the RNDR instruction if the CPU supports it */
+ if (is_armv8_5_rng_present()) {
+ return read_rndr();
+ }
+#endif
+
/*
- * Ideally, a random number should be returned instead of the
+ * Ideally, a random number should be returned above. If a random
+ * number generator is not supported, return instead a
* combination of a timer's value and a compile-time constant.
- * As the virt platform does not have any random number generator,
- * this is better than nothing but not necessarily really secure.
+ * This is better than nothing but not necessarily really secure.
*/
return RANDOM_CANARY_VALUE ^ read_cntpct_el0();
}