[PATCHv2] arm: mm: Poison freed init memory

[Stephen Boyd]

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 at codeaurora.org>
---

On 7/6/2011 2:01 PM, Russell King - ARM Linux wrote:
> On Wed, Jul 06, 2011 at 01:55:54PM -0700, Stephen Boyd wrote:
>> Should it include the initrd too? At least x86 poisons that memory but I
>> don't know who would be using that incorrectly.
>
> It could do - I don't see any harm in not doing so.  The only issue
> is that people may want to disable this stuff if they're after
> squeezing every last ms out of the boot time.

I haven't done this. I hope a follow up patch will suffice.

>
>> How about a free_init_area() function which calls free_area() after
>> poisoning the memory?
>
> I need to go back and look at the Integrator etc situation with regard
> to reorganizing the vmlinux layout - it may be that the omission of
> freeing .init memory can now be removed (it was there to stop the
> memory being used as the first K of memory wasn't DMA-able.)
>
> Assuming it has to stay though, we still should arrange for the initrd
> memory to be poisoned even if it isn't freed.

Is this is patch what you're saying? I would have liked to do a
free_init_area() wrapper, but until the Integrator situation can be
sorted it doesn't look worthwhile.

 arch/arm/mm/init.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index c19571c..d6360b1 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -422,6 +422,17 @@ 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)
 {
@@ -704,11 +715,13 @@ 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)),
@@ -721,10 +734,12 @@ 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)
-- 
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