ARM: 6996/1: mm: Poison freed init memory

Poisoning __init marked memory can be useful when tracking down
obscure memory corruption bugs. Therefore, poison init memory
with 0xe7fddef0 to catch bugs earlier. The poison value is an
undefined instruction in ARM mode and branch to an undefined
instruction in Thumb mode.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/init.c

@@ -416,6 +416,17 @@ static inline int free_area(unsigned long pfn, unsigned long end, char *s)
 	return pages;
 }
 
+/*
+ * Poison init memory with an undefined instruction (ARM) or a branch to an
+ * undefined instruction (Thumb).
+ */
+static inline void poison_init_mem(void *s, size_t count)
+{
+	u32 *p = (u32 *)s;
+	while ((count = count - 4))
+		*p++ = 0xe7fddef0;
+}
+
 static inline void
 free_memmap(unsigned long start_pfn, unsigned long end_pfn)
 {
@@ -696,11 +707,13 @@ void free_initmem(void)
 #ifdef CONFIG_HAVE_TCM
 	extern char __tcm_start, __tcm_end;
 
+	poison_init_mem(&__tcm_start, &__tcm_end - &__tcm_start);
 	totalram_pages += free_area(__phys_to_pfn(__pa(&__tcm_start)),
 				    __phys_to_pfn(__pa(&__tcm_end)),
 				    "TCM link");
 #endif
 
+	poison_init_mem(__init_begin, __init_end - __init_begin);
 	if (!machine_is_integrator() && !machine_is_cintegrator())
 		totalram_pages += free_area(__phys_to_pfn(__pa(__init_begin)),
 					    __phys_to_pfn(__pa(__init_end)),
@@ -713,10 +726,12 @@ static int keep_initrd;
 
 void free_initrd_mem(unsigned long start, unsigned long end)
 {
-	if (!keep_initrd)
+	if (!keep_initrd) {
+		poison_init_mem((void *)start, PAGE_ALIGN(end) - start);
 		totalram_pages += free_area(__phys_to_pfn(__pa(start)),
 					    __phys_to_pfn(__pa(end)),
 					    "initrd");
+	}
 }
 
 static int __init keepinitrd_setup(char *__unused)