[U-Boot] [RFC PATCH 2/2] ARM: Introduce ability to enable invalidate of BTB on Cortex-A15 for CVE-2017-5715

[Nishanth Menon]

As recommended by Arm in [1], ACR needs to be set[2] to enable
invalidation of BTB. This has to be enabled unconditionally for
ICIALLU to be functional on Cortex-A15 processors. Provide a config
option for platforms to enable this option based on impact analysis
for products.

NOTE: This patch in itself is NOT the final solution, this requires:
a) Implementation of v7_arch_cp15_set_acr on SoCs which may not
   provide direct access to ACR register.
b) Operating Systems such as Linux to provide adequate workaround in the
   right locations.

[1] https://developer.arm.com/support/security-update
[2] http://infocenter.arm.com/help/topic/com.arm.doc.ddi0438c/BABGHIBG.html

Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Russell King <linux at arm.linux.org.uk>
Cc: Tony Lindgren <tony at atomide.com>
Cc: Robin Murphy <robin.murphy at arm.com>
Cc: Florian Fainelli <f.fainelli at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Christoffer Dall <christoffer.dall at linaro.org>
Cc: Andre Przywara <Andre.Przywara at arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
Cc: Tom Rini <trini at konsulko.com>
Cc: Michael Nazzareno Trimarchi <michael at amarulasolutions.com>

Signed-off-by: Nishanth Menon <nm at ti.com>
---
 arch/arm/Kconfig           | 4 ++++
 arch/arm/cpu/armv7/start.S | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index c2ac0fef9d0c..116cee559ca4 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -87,6 +87,7 @@ config THUMB2_KERNEL
 # CONFIG_ARM_ERRATA_798870
 # CONFIG_ARM_ERRATA_801819
 # CONFIG_ARM_CORTEX_A8_CVE_2017_5715
+# CONFIG_ARM_CORTEX_A15_CVE_2017_5715
 
 config ARM_ERRATA_430973
 	bool
@@ -160,6 +161,9 @@ config ARM_ERRATA_855873
 config ARM_CORTEX_A8_CVE_2017_5715
 	bool
 
+config ARM_CORTEX_A15_CVE_2017_5715
+	bool
+
 config CPU_ARM720T
 	bool
 	select SYS_CACHE_SHIFT_5
diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
index 64c5d7598dea..4835316bb37e 100644
--- a/arch/arm/cpu/armv7/start.S
+++ b/arch/arm/cpu/armv7/start.S
@@ -238,6 +238,14 @@ skip_errata_798870:
 skip_errata_801819:
 #endif
 
+#ifdef CONFIG_ARM_CORTEX_A15_CVE_2017_5715
+	mrc	p15, 0, r0, c1, c0, 1	@ read auxilary control register
+	orr	r0, r0, #1 << 0		@ Enable invalidates of BTB
+	push	{r1-r5}			@ Save the cpu info registers
+	bl	v7_arch_cp15_set_acr
+	pop	{r1-r5}			@ Restore the cpu info - fall through
+#endif
+
 #ifdef CONFIG_ARM_ERRATA_454179
 	mrc	p15, 0, r0, c1, c0, 1	@ Read ACR
 
-- 
2.15.1