Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized memory in __alloc_skb

Eric Dumazet
2011-04-19T20:17:58Z

Le mardi 19 avril 2011 à 12:10 -0500, Christoph Lameter a écrit :
> On Tue, 19 Apr 2011, Eric Dumazet wrote:
>
> > }
> > }
> >
> > -#ifdef CONFIG_CMPXCHG_LOCAL
> > +#if defined(CONFIG_CMPXCHG_LOCAL) && \
> > + !defined(CONFIG_KMEMCHECK) && !defined(DEBUG_PAGEALLOC)
> > +#define SLUB_USE_CMPXCHG_DOUBLE
> > +#endif
> > +
> > +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> > #ifdef CONFIG_PREEMPT
> > /*
>
> Ugg.. Isnt there some way to indicate to kmemcheck that a speculative
> access is occurring?

Yes, here is a totally untested patch (only compiled here), to keep
kmemcheck & cmpxchg_double together.

diff --git a/mm/slub.c b/mm/slub.c
index 94d2a33..43c08c7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -261,6 +261,14 @@ static inline void *get_freepointer(struct kmem_cache *s, void *object)
return *(void **)(object + s->offset);
}

+static inline void *get_freepointer_mark(struct kmem_cache *s, void *object)
+{
+ void *ptr = object + s->offset;
+
+ kmemcheck_mark_initialized(ptr, sizeof(void *));
+ return *(void **)ptr;
+}
+
static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
{
*(void **)(object + s->offset) = fp;
@@ -1540,7 +1548,11 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
}
}

-#ifdef CONFIG_CMPXCHG_LOCAL
+#if defined(CONFIG_CMPXCHG_LOCAL) && !defined(DEBUG_PAGEALLOC)
+#define SLUB_USE_CMPXCHG_DOUBLE
+#endif
+
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
#ifdef CONFIG_PREEMPT
/*
* Calculate the next globally unique transaction for disambiguiation
@@ -1604,7 +1616,7 @@ static inline void note_cmpxchg_failure(const char *n,

void init_kmem_cache_cpus(struct kmem_cache *s)
{
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
int cpu;

for_each_possible_cpu(cpu)
@@ -1643,7 +1655,7 @@ static void deactivate_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
page->inuse--;
}
c->page = NULL;
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
c->tid = next_tid(c->tid);
#endif
unfreeze_slab(s, page, tail);
@@ -1780,7 +1792,7 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
{
void **object;
struct page *new;
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
unsigned long flags;

local_irq_save(flags);
@@ -1819,7 +1831,7 @@ load_freelist:
c->node = page_to_nid(c->page);
unlock_out:
slab_unlock(c->page);
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
c->tid = next_tid(c->tid);
local_irq_restore(flags);
#endif
@@ -1858,7 +1870,7 @@ new_slab:
}
if (!(gfpflags & __GFP_NOWARN) && printk_ratelimit())
slab_out_of_memory(s, gfpflags, node);
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
local_irq_restore(flags);
#endif
return NULL;
@@ -1887,7 +1899,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
{
void **object;
struct kmem_cache_cpu *c;
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
unsigned long tid;
#else
unsigned long flags;
@@ -1896,7 +1908,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
if (slab_pre_alloc_hook(s, gfpflags))
return NULL;

-#ifndef CONFIG_CMPXCHG_LOCAL
+#ifndef SLUB_USE_CMPXCHG_DOUBLE
local_irq_save(flags);
#else
redo:
@@ -1910,7 +1922,7 @@ redo:
*/
c = __this_cpu_ptr(s->cpu_slab);

-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
/*
* The transaction ids are globally unique per cpu and per operation on
* a per cpu queue. Thus they can be guarantee that the cmpxchg_double
@@ -1927,7 +1939,7 @@ redo:
object = __slab_alloc(s, gfpflags, node, addr, c);

else {
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
/*
* The cmpxchg will only match if there was no additional
* operation and if we are on the right processor.
@@ -1943,7 +1955,8 @@ redo:
if (unlikely(!this_cpu_cmpxchg_double(
s->cpu_slab->freelist, s->cpu_slab->tid,
object, tid,
- get_freepointer(s, object), next_tid(tid)))) {
+ get_freepointer_mark(s, object),
+ next_tid(tid)))) {

note_cmpxchg_failure("slab_alloc", s, tid);
goto redo;
@@ -1954,7 +1967,7 @@ redo:
stat(s, ALLOC_FASTPATH);
}

-#ifndef CONFIG_CMPXCHG_LOCAL
+#ifndef SLUB_USE_CMPXCHG_DOUBLE
local_irq_restore(flags);
#endif

@@ -2034,7 +2047,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
{
void *prior;
void **object = (void *)x;
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
unsigned long flags;

local_irq_save(flags);
@@ -2070,7 +2083,7 @@ checks_ok:

out_unlock:
slab_unlock(page);
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
local_irq_restore(flags);
#endif
return;
@@ -2084,7 +2097,7 @@ slab_empty:
stat(s, FREE_REMOVE_PARTIAL);
}
slab_unlock(page);
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
local_irq_restore(flags);
#endif
stat(s, FREE_SLAB);
@@ -2113,7 +2126,7 @@ static __always_inline void slab_free(struct kmem_cache *s,
{
void **object = (void *)x;
struct kmem_cache_cpu *c;
-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
unsigned long tid;
#else
unsigned long flags;
@@ -2121,7 +2134,7 @@ static __always_inline void slab_free(struct kmem_cache *s,

slab_free_hook(s, x);

-#ifndef CONFIG_CMPXCHG_LOCAL
+#ifndef SLUB_USE_CMPXCHG_DOUBLE
local_irq_save(flags);

#else
@@ -2136,7 +2149,7 @@ redo:
*/
c = __this_cpu_ptr(s->cpu_slab);

-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
tid = c->tid;
barrier();
#endif
@@ -2144,7 +2157,7 @@ redo:
if (likely(page == c->page && c->node != NUMA_NO_NODE)) {
set_freepointer(s, object, c->freelist);

-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
if (unlikely(!this_cpu_cmpxchg_double(
s->cpu_slab->freelist, s->cpu_slab->tid,
c->freelist, tid,
@@ -2160,7 +2173,7 @@ redo:
} else
__slab_free(s, page, x, addr);

-#ifndef CONFIG_CMPXCHG_LOCAL
+#ifndef SLUB_USE_CMPXCHG_DOUBLE
local_irq_restore(flags);
#endif
}
@@ -2354,7 +2367,7 @@ static inline int alloc_kmem_cache_cpus(struct kmem_cache *s)
BUILD_BUG_ON(PERCPU_DYNAMIC_EARLY_SIZE <
SLUB_PAGE_SHIFT * sizeof(struct kmem_cache_cpu));

-#ifdef CONFIG_CMPXCHG_LOCAL
+#ifdef SLUB_USE_CMPXCHG_DOUBLE
/*
* Must align to double word boundary for the double cmpxchg instructions
* to work.