ARM: 6468/1: backtrace: fix calculation of thread stack base

When unwinding stack frames we must take care not to unwind
areas of memory that lie outside of the known extent of the stack.

This patch fixes an incorrect calculation of the stack base where
THREAD_SIZE is added to the stack pointer after it has already
been aligned to this value. Since the ALIGN macro performs this
addition internally, we end up overshooting the base by 8k.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/stacktrace.c

@@ -28,7 +28,7 @@ int notrace unwind_frame(struct stackframe *frame)
 
 	/* only go to a higher address on the stack */
 	low = frame->sp;
-	high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;
+	high = ALIGN(low, THREAD_SIZE);
 
 	/* check current frame pointer is within bounds */
 	if (fp < (low + 12) || fp + 4 >= high)

arch/arm/kernel/unwind.c

@@ -279,7 +279,7 @@ int unwind_frame(struct stackframe *frame)
 
 	/* only go to a higher address on the stack */
 	low = frame->sp;
-	high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;
+	high = ALIGN(low, THREAD_SIZE);
 
 	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
 		 frame->pc, frame->lr, frame->sp);