core: arm: make alignment check configurable

We occasionally get reports from people stumbling upon data abort
exceptions caused by alignment faults in TAs. The recommended fix is to
change the code so that the unaligned access won't occur. But it is
sometimes difficult to achieve.

Therefore we provide a compile-time option to disable alignment checks.
For AArch64 it applies to both SEL1 and SEL0.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Tested-by: Jerome Forissier <jerome.forissier@linaro.org> (HiKey)
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>

5 files changed, 36 insertions, 15 deletions

diff --git a/core/arch/arm/arm.mk b/core/arch/arm/arm.mk
index 13361d8a..40253d06 100644
--- a/core/arch/arm/arm.mk
+++ b/core/arch/arm/arm.mk
@@ -31,6 +31,8 @@ CFG_CORE_RODATA_NOEXEC ?= n
 ifeq ($(CFG_CORE_RODATA_NOEXEC),y)
 $(call force,CFG_CORE_RWDATA_NOEXEC,y)
 endif
+# 'y' to set the Alignment Check Enable bit in SCTLR/SCTLR_EL1, 'n' to clear it
+CFG_SCTLR_ALIGNMENT_CHECK ?= y
 
 ifeq ($(CFG_WITH_PAGER),y)
 ifeq ($(CFG_CORE_SANITIZE_KADDRESS),y)
diff --git a/core/arch/arm/kernel/generic_entry_a32.S b/core/arch/arm/kernel/generic_entry_a32.S
index 6100bb88..005d85c4 100644
--- a/core/arch/arm/kernel/generic_entry_a32.S
+++ b/core/arch/arm/kernel/generic_entry_a32.S
@@ -187,7 +187,11 @@ UNWIND(	.cantunwind)
 
 	/* Enable alignment checks and disable data and instruction cache. */
 	read_sctlr r0
+#if defined(CFG_SCTLR_ALIGNMENT_CHECK)
 	orr	r0, r0, #SCTLR_A
+#else
+	bic	r0, r0, #SCTLR_A
+#endif
 	bic	r0, r0, #SCTLR_C
 	bic	r0, r0, #SCTLR_I
 #if defined(CFG_HWSUPP_MEM_PERM_WXN) && defined(CFG_CORE_RWDATA_NOEXEC)
@@ -457,7 +461,11 @@ UNWIND(	.cantunwind)
 	mov	r5, r1
 	mov	r6, lr
 	read_sctlr r0
+#if defined(CFG_SCTLR_ALIGNMENT_CHECK)
 	orr	r0, r0, #SCTLR_A
+#else
+	bic	r0, r0, #SCTLR_A
+#endif
 #if defined(CFG_HWSUPP_MEM_PERM_WXN) && defined(CFG_CORE_RWDATA_NOEXEC)
 	orr	r0, r0, #(SCTLR_WXN | SCTLR_UWXN)
 #endif
diff --git a/core/arch/arm/kernel/generic_entry_a64.S b/core/arch/arm/kernel/generic_entry_a64.S
index 7221ad1b..b7290e6c 100644
--- a/core/arch/arm/kernel/generic_entry_a64.S
+++ b/core/arch/arm/kernel/generic_entry_a64.S
@@ -58,6 +58,21 @@
 		msr	spsel, #0
 	.endm
 
+	.macro set_sctlr_el1
+		mrs	x0, sctlr_el1
+		orr	x0, x0, #SCTLR_I
+		orr	x0, x0, #SCTLR_SA
+#if defined(CFG_CORE_RWDATA_NOEXEC)
+		orr	x0, x0, #SCTLR_WXN
+#endif
+#if defined(CFG_SCTLR_ALIGNMENT_CHECK)
+		orr	x0, x0, #SCTLR_A
+#else
+		bic	x0, x0, #SCTLR_A
+#endif
+		msr	sctlr_el1, x0
+	.endm
+
 .section .text.boot
 FUNC _start , :
 	mov	x19, x0		/* Save pagable part address */
@@ -67,13 +82,7 @@ FUNC _start , :
 	msr	vbar_el1, x0
 	isb
 
-	mrs	x0, sctlr_el1
-	mov	x1, #(SCTLR_I | SCTLR_A | SCTLR_SA)
-#if defined(CFG_CORE_RWDATA_NOEXEC)
-	orr	x1, x1, #SCTLR_WXN
-#endif
-	orr	x0, x0, x1
-	msr	sctlr_el1, x0
+	set_sctlr_el1
 	isb
 
 #ifdef CFG_WITH_PAGER
@@ -186,13 +195,7 @@ FUNC cpu_on_handler , :
 	msr	vbar_el1, x0
 	isb
 
-	mrs	x0, sctlr_el1
-	mov	x1, #(SCTLR_I | SCTLR_A | SCTLR_SA)
-#if defined(CFG_CORE_RWDATA_NOEXEC)
-	orr	x1, x1, #SCTLR_WXN
-#endif
-	orr	x0, x0, x1
-	msr	sctlr_el1, x0
+	set_sctlr_el1
 	isb
 
 	/* Setup SP_EL0 and SP_EL1, SP will be set to SP_EL0 */
diff --git a/core/arch/arm/plat-sunxi/entry.S b/core/arch/arm/plat-sunxi/entry.S
index 5b1dc392..d015ee6e 100644
--- a/core/arch/arm/plat-sunxi/entry.S
+++ b/core/arch/arm/plat-sunxi/entry.S
@@ -52,7 +52,11 @@ LOCAL_FUNC reset , :
 UNWIND(	.fnstart)
 UNWIND(	.cantunwind)
         read_sctlr  r0
-	orr	    r0, r0, #SCTLR_A
+#if defined(CFG_SCTLR_ALIGNMENT_CHECK)
+	orr	r0, r0, #SCTLR_A
+#else
+	bic	r0, r0, #SCTLR_A
+#endif
 	write_sctlr r0
 
 	ldr	   r0, =_start
diff --git a/core/arch/arm/plat-sunxi/smp_boot.S b/core/arch/arm/plat-sunxi/smp_boot.S
index 98c63a59..da93d7de 100644
--- a/core/arch/arm/plat-sunxi/smp_boot.S
+++ b/core/arch/arm/plat-sunxi/smp_boot.S
@@ -50,7 +50,11 @@ UNWIND(	.fnstart)
 UNWIND(	.cantunwind)
 	/* secondary CPUs internal initialization */
 	read_sctlr r0
+#if defined(CFG_SCTLR_ALIGNMENT_CHECK)
 	orr	r0, r0, #SCTLR_A
+#else
+	bic	r0, r0, #SCTLR_A
+#endif
 	write_sctlr r0
 	
 	/* install smp initialization vector */