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authorMark Brown <broonie@kernel.org>2020-01-21 15:58:53 +0300
committerWill Deacon <will@kernel.org>2020-01-22 12:54:52 +0300
commit2e8e1ea88cbcb19a77b7acb67f6ffe39cc15740c (patch)
tree24b908d1f3608e4bebf845d9b3202d83e5881beb
parent1a50ec0b3b2e9a83f1b1245ea37a853aac2f741c (diff)
downloadlinux-2e8e1ea88cbcb19a77b7acb67f6ffe39cc15740c.tar.xz
arm64: Use v8.5-RNG entropy for KASLR seed
When seeding KALSR on a system where we have architecture level random number generation make use of that entropy, mixing it in with the seed passed by the bootloader. Since this is run very early in init before feature detection is complete we open code rather than use archrandom.h. Signed-off-by: Mark Brown <broonie@kernel.org> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Will Deacon <will@kernel.org>
-rw-r--r--arch/arm64/include/asm/archrandom.h8
-rw-r--r--arch/arm64/kernel/kaslr.c11
2 files changed, 19 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
index 5ea5a1ce5a5f..3fe02da70004 100644
--- a/arch/arm64/include/asm/archrandom.h
+++ b/arch/arm64/include/asm/archrandom.h
@@ -59,9 +59,17 @@ static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
return ok;
}
+static inline bool __init __early_cpu_has_rndr(void)
+{
+ /* Open code as we run prior to the first call to cpufeature. */
+ unsigned long ftr = read_sysreg_s(SYS_ID_AA64ISAR0_EL1);
+ return (ftr >> ID_AA64ISAR0_RNDR_SHIFT) & 0xf;
+}
+
#else
static inline bool __arm64_rndr(unsigned long *v) { return false; }
+static inline bool __init __early_cpu_has_rndr(void) { return false; }
#endif /* CONFIG_ARCH_RANDOM */
#endif /* _ASM_ARCHRANDOM_H */
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 2a11a962e571..53b8a4ee64ff 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -120,6 +120,17 @@ u64 __init kaslr_early_init(u64 dt_phys)
return 0;
}
+ /*
+ * Mix in any entropy obtainable architecturally, open coded
+ * since this runs extremely early.
+ */
+ if (__early_cpu_has_rndr()) {
+ unsigned long raw;
+
+ if (__arm64_rndr(&raw))
+ seed ^= raw;
+ }
+
if (!seed) {
kaslr_status = KASLR_DISABLED_NO_SEED;
return 0;