Re: WARNING: kmemcheck: Caught 32-bit read from uninitializedmemory (f6f6e1a4), by kmemleak's scan_block()

From: Pekka Enberg
Date: Tue Aug 25 2009 - 04:45:26 EST


On Tue, 2009-08-25 at 10:32 +0200, Ingo Molnar wrote:
> > In any case, I don't think it is very productive to run them both
> > at the same time, simply because kmemcheck slows every memory
> > access down so much and scanning memory doesn't exactly help that.
> > It _could_ be useful to have them compiled into the same kernel,
> > though, e.g. a distro "-debug" kernel.
> >
> > Maybe you can just add the "depends on !KMEMLEAK" to
> > CONFIG_KMEMCHECK in tip/out-of-tree for now?
>
> i think it would be far more intelligent to annotate those accesses
> by kmemleak as 'trust me, dont check'. Willing to test such a patch.

I guess something like this totally untested patch should do it. Vegard,
Catalin?

Pekka

diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c
index 2c55ed0..528bf95 100644
--- a/arch/x86/mm/kmemcheck/kmemcheck.c
+++ b/arch/x86/mm/kmemcheck/kmemcheck.c
@@ -331,6 +331,20 @@ static void kmemcheck_read_strict(struct pt_regs *regs,
kmemcheck_shadow_set(shadow, size);
}

+bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
+{
+ enum kmemcheck_shadow status;
+ void *shadow;
+
+ shadow = kmemcheck_shadow_lookup(addr);
+ if (!shadow)
+ return true;
+
+ status = kmemcheck_shadow_test(shadow, size);
+
+ return status == KMEMCHECK_SHADOW_INITIALIZED;
+}
+
/* Access may cross page boundary */
static void kmemcheck_read(struct pt_regs *regs,
unsigned long addr, unsigned int size)
diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h
index 47b39b7..dc2fd54 100644
--- a/include/linux/kmemcheck.h
+++ b/include/linux/kmemcheck.h
@@ -34,6 +34,8 @@ void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n);
int kmemcheck_show_addr(unsigned long address);
int kmemcheck_hide_addr(unsigned long address);

+bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size);
+
#else
#define kmemcheck_enabled 0

@@ -99,6 +101,11 @@ static inline void kmemcheck_mark_initialized_pages(struct page *p,
{
}

+static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
+{
+ return true;
+}
+
#endif /* CONFIG_KMEMCHECK */

/*
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 4872673..c14d6e4 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -97,6 +97,7 @@
#include <asm/processor.h>
#include <asm/atomic.h>

+#include <linux/kmemcheck.h>
#include <linux/kmemleak.h>

/*
@@ -949,6 +950,8 @@ static void scan_object(struct kmemleak_object *object)
if (!(object->flags & OBJECT_ALLOCATED))
/* already freed object */
goto out;
+ if (!kmemcheck_is_obj_initialized(object->pointer, object->size))
+ goto out;
if (hlist_empty(&object->area_list))
scan_block((void *)object->pointer,
(void *)(object->pointer + object->size), object, 0);


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