ARM: 7876/1: clear Thumb-2 IT state on exception handling

The exception handling code fails to clear the IT state, potentially
leading to incorrect execution of the fixup if the size of the IT
block is more than one.

Let fixup_exception do the IT sanitizing if a fixup has been found,
and restore CPSR from the stack when returning from a data abort.

Cc: Will Deacon <will.deacon@arm.com>
Cc: stable@vger.kernel.org
Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/entry-armv.S

@@ -192,6 +192,7 @@ __dabt_svc:
 	svc_entry
 	mov	r2, sp
 	dabt_helper
+ THUMB(	ldr	r5, [sp, #S_PSR]	)	@ potentially updated CPSR
 	svc_exit r5				@ return from exception
  UNWIND(.fnend		)
 ENDPROC(__dabt_svc)

arch/arm/mm/extable.c

@@ -9,8 +9,13 @@ int fixup_exception(struct pt_regs *regs)
 	const struct exception_table_entry *fixup;
 
 	fixup = search_exception_tables(instruction_pointer(regs));
-	if (fixup)
+	if (fixup) {
 		regs->ARM_pc = fixup->fixup;
+#ifdef CONFIG_THUMB2_KERNEL
+		/* Clear the IT state to avoid nasty surprises in the fixup */
+		regs->ARM_cpsr &= ~PSR_IT_MASK;
+#endif
+	}
 
 	return fixup != NULL;
 }