Update macro to check need for CVE-2017-5715 mitigation

Armv8.5 introduces the field CSV2 to register ID_AA64PFR0_EL1. It can
have the following 3 values:

- 0: Branch targets trained in one hardware described context may affect
     speculative execution in a different hardware described context. In
     some CPUs it may be needed to apply mitigations.

- 1: Branch targets trained in one hardware described context can only
     affect speculative execution in a different hardware described
     context in a hard-to-determine way. No mitigation required.

- 2: Same as 1, but the device is also aware of SCXTNUM_ELx register
     contexts. The TF doesn't use the registers, so there is no
     difference with 1.

The field CSV2 was originally introduced in the TRM of the Cortex-A76
before the release of the Armv8.5 architecture. That TRM only mentions
the meaning of values 0 and 1. Because of this, the code only checks if
the field has value 1 to know whether to enable or disable the
mitigations.

This patch makes it aware of value 2 as well. Both values 1 and 2
disable the mitigation, and 0 enables it.

Change-Id: I5af33de25a0197c98173f52c6c8c77b51a51429f
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

diff --git a/include/lib/cpus/aarch64/cpu_macros.S b/include/lib/cpus/aarch64/cpu_macros.S
index b907668b3b3ef26c2f733b9239076b7c5d15e708..044aacaf41fa771be3a4c79a8f6cec3d88f9277f 100644 (file)
--- a/include/lib/cpus/aarch64/cpu_macros.S
+++ b/include/lib/cpus/aarch64/cpu_macros.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2014-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,6 +7,7 @@
 #define CPU_MACROS_S
 
 #include <arch.h>
+#include <assert_macros.S>
 #include <lib/cpus/errata_report.h>
 
 #define CPU_IMPL_PN_MASK       (MIDR_IMPL_MASK << MIDR_IMPL_SHIFT) | \
@@ -263,11 +264,22 @@
        mrs     \_reg, id_aa64pfr0_el1
        ubfx    \_reg, \_reg, #ID_AA64PFR0_CSV2_SHIFT, #ID_AA64PFR0_CSV2_LENGTH
        /*
-        * If the field equals to 1 then branch targets trained in one
-        * context cannot affect speculative execution in a different context.
+        * If the field equals 1, branch targets trained in one context cannot
+        * affect speculative execution in a different context.
+        *
+        * If the field equals 2, it means that the system is also aware of
+        * SCXTNUM_ELx register contexts. We aren't using them in the TF, so we
+        * expect users of the registers to do the right thing.
+        *
+        * Only apply mitigations if the value of this field is 0.
         */
-       cmp     \_reg, #1
-       beq     \_label
+#if ENABLE_ASSERTIONS
+       cmp     \_reg, #3 /* Only values 0 to 2 are expected */
+       ASM_ASSERT(lo)
+#endif
+
+       cmp     \_reg, #0
+       bne     \_label
        .endm
 
        /*