Re: [PATCH v2 1/3] rcu/kasan: record and print call_rcu() call stack

[Walter Wu]

On Mon, 2020-05-11 at 11:05 -0700, Paul E. McKenney wrote:
> On Mon, May 11, 2020 at 10:31:11AM +0800, Walter Wu wrote:
> > This feature will record first and last call_rcu() call stack and
> > print two call_rcu() call stack in KASAN report.
> 
> Suppose that a given rcu_head structure is passed to call_rcu(), then
> the grace period elapses, the callback is invoked, and the enclosing
> data structure is freed.  But then that same region of memory is
> immediately reallocated as the same type of structure and again
> passed to call_rcu(), and that this cycle repeats several times.
> 
> Would the first call stack forever be associated with the first
> call_rcu() in this series?  If so, wouldn't the last two usually
> be the most useful?  Or am I unclear on the use case?
> 

The first call stack doesn't forever associate with first call_rcu(),
if someone object freed and reallocated, then the first call stack will
replace with new object.

> > When call_rcu() is called, we store the call_rcu() call stack into
> > slub alloc meta-data, so that KASAN report can print rcu stack.
> > 
> > It doesn't increase the cost of memory consumption. Because we don't
> > enlarge struct kasan_alloc_meta size.
> > - add two call_rcu() call stack into kasan_alloc_meta, size is 8 bytes.
> > - remove free track from kasan_alloc_meta, size is 8 bytes.
> > 
> > [1]https://bugzilla.kernel.org/show_bug.cgi?id=198437
> > [2]https://groups.google.com/forum/#!searchin/kasan-dev/better$20stack$20traces$20for$20rcu%7Csort:date/kasan-dev/KQsjT_88hDE/7rNUZprRBgAJ
> > 
> > Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
> > Suggested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> > Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> > ---
> >  include/linux/kasan.h |  2 ++
> >  kernel/rcu/tree.c     |  3 +++
> >  lib/Kconfig.kasan     |  2 ++
> >  mm/kasan/common.c     |  4 ++--
> >  mm/kasan/generic.c    | 29 +++++++++++++++++++++++++++++
> >  mm/kasan/kasan.h      | 19 +++++++++++++++++++
> >  mm/kasan/report.c     | 21 +++++++++++++++++----
> >  7 files changed, 74 insertions(+), 6 deletions(-)
> > 
> > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > index 31314ca7c635..23b7ee00572d 100644
> > --- a/include/linux/kasan.h
> > +++ b/include/linux/kasan.h
> > @@ -174,11 +174,13 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
> >  
> >  void kasan_cache_shrink(struct kmem_cache *cache);
> >  void kasan_cache_shutdown(struct kmem_cache *cache);
> > +void kasan_record_aux_stack(void *ptr);
> >  
> >  #else /* CONFIG_KASAN_GENERIC */
> >  
> >  static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
> >  static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
> > +static inline void kasan_record_aux_stack(void *ptr) {}
> >  
> >  #endif /* CONFIG_KASAN_GENERIC */
> >  
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 06548e2ebb72..de872b6cc261 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -57,6 +57,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/sched/isolation.h>
> >  #include <linux/sched/clock.h>
> > +#include <linux/kasan.h>
> >  #include "../time/tick-internal.h"
> >  
> >  #include "tree.h"
> > @@ -2694,6 +2695,8 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
> >  		trace_rcu_callback(rcu_state.name, head,
> >  				   rcu_segcblist_n_cbs(&rdp->cblist));
> >  
> > +	kasan_record_aux_stack(head);
> 
> Just for the record, at this point we have not yet queued the callback.
> We have also not yet disabled interrupts.  Which might be OK, but I
> figured I should call out the possibility of moving this down a few
> lines to follow the local_irq_save().
> 

We will intend to do it.

> If someone incorrectly invokes concurrently invokes call_rcu() on this
> same region of memory, possibly from an interrupt handler, we are OK
> corrupting the stack traces, right?
> 

Yes, and the wrong invoking call_rcu should be recorded.

> But what happens if a given structure has more than one rcu_head
> structure?  In that case, RCU would be just fine with it being
> concurrently passed to different call_rcu() invocations as long as the
> two invocations didn't both use the same rcu_head structure.  (In that
> case, they had best not be both freeing the object, and if even one of
> them is freeing the object, coordination is necessary.)
> 
> If this is a problem, one approach would be to move the
> kasan_record_aux_stack(head) call to kfree_rcu().  After all, it is
> definitely illegal to pass the same memory to a pair of kfree_rcu()
> invocations!  ;-)
> 

The function of kasan_record_aux_stack(head) is simple, it is only to
record call stack by the 'head' object.


Thanks.

> 							Thanx, Paul
> 
> > +
> >  	/* Go handle any RCU core processing required. */
> >  	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
> >  	    unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
> > diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> > index 81f5464ea9e1..56a89291f1cc 100644
> > --- a/lib/Kconfig.kasan
> > +++ b/lib/Kconfig.kasan
> > @@ -58,6 +58,8 @@ config KASAN_GENERIC
> >  	  For better error detection enable CONFIG_STACKTRACE.
> >  	  Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
> >  	  (the resulting kernel does not boot).
> > +	  Currently CONFIG_KASAN_GENERIC will print first and last call_rcu()
> > +	  call stack. It doesn't increase the cost of memory consumption.
> >  
> >  config KASAN_SW_TAGS
> >  	bool "Software tag-based mode"
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 2906358e42f0..8bc618289bb1 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -41,7 +41,7 @@
> >  #include "kasan.h"
> >  #include "../slab.h"
> >  
> > -static inline depot_stack_handle_t save_stack(gfp_t flags)
> > +depot_stack_handle_t kasan_save_stack(gfp_t flags)
> >  {
> >  	unsigned long entries[KASAN_STACK_DEPTH];
> >  	unsigned int nr_entries;
> > @@ -54,7 +54,7 @@ static inline depot_stack_handle_t save_stack(gfp_t flags)
> >  static inline void set_track(struct kasan_track *track, gfp_t flags)
> >  {
> >  	track->pid = current->pid;
> > -	track->stack = save_stack(flags);
> > +	track->stack = kasan_save_stack(flags);
> >  }
> >  
> >  void kasan_enable_current(void)
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index 56ff8885fe2e..b86880c338e2 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -325,3 +325,32 @@ DEFINE_ASAN_SET_SHADOW(f2);
> >  DEFINE_ASAN_SET_SHADOW(f3);
> >  DEFINE_ASAN_SET_SHADOW(f5);
> >  DEFINE_ASAN_SET_SHADOW(f8);
> > +
> > +void kasan_record_aux_stack(void *addr)
> > +{
> > +	struct page *page = kasan_addr_to_page(addr);
> > +	struct kmem_cache *cache;
> > +	struct kasan_alloc_meta *alloc_info;
> > +	void *object;
> > +
> > +	if (!(page && PageSlab(page)))
> > +		return;
> > +
> > +	cache = page->slab_cache;
> > +	object = nearest_obj(cache, page, addr);
> > +	alloc_info = get_alloc_info(cache, object);
> > +
> > +	if (!alloc_info->rcu_stack[0])
> > +		/* record first call_rcu() call stack */
> > +		alloc_info->rcu_stack[0] = kasan_save_stack(GFP_NOWAIT);
> > +	else
> > +		/* record last call_rcu() call stack */
> > +		alloc_info->rcu_stack[1] = kasan_save_stack(GFP_NOWAIT);
> > +}
> > +
> > +struct kasan_track *kasan_get_aux_stack(struct kasan_alloc_meta *alloc_info,
> > +						u8 idx)
> > +{
> > +	return container_of(&alloc_info->rcu_stack[idx],
> > +						struct kasan_track, stack);
> > +}
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index e8f37199d885..1cc1fb7b0de3 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -96,15 +96,28 @@ struct kasan_track {
> >  	depot_stack_handle_t stack;
> >  };
> >  
> > +#ifdef CONFIG_KASAN_GENERIC
> > +#define SIZEOF_PTR sizeof(void *)
> > +#define KASAN_NR_RCU_CALL_STACKS 2
> > +#else /* CONFIG_KASAN_GENERIC */
> >  #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> >  #define KASAN_NR_FREE_STACKS 5
> >  #else
> >  #define KASAN_NR_FREE_STACKS 1
> >  #endif
> > +#endif /* CONFIG_KASAN_GENERIC */
> >  
> >  struct kasan_alloc_meta {
> >  	struct kasan_track alloc_track;
> > +#ifdef CONFIG_KASAN_GENERIC
> > +	/*
> > +	 * call_rcu() call stack is stored into struct kasan_alloc_meta.
> > +	 * The free stack is stored into freed object.
> > +	 */
> > +	depot_stack_handle_t rcu_stack[KASAN_NR_RCU_CALL_STACKS];
> > +#else
> >  	struct kasan_track free_track[KASAN_NR_FREE_STACKS];
> > +#endif
> >  #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
> >  	u8 free_pointer_tag[KASAN_NR_FREE_STACKS];
> >  	u8 free_track_idx;
> > @@ -159,16 +172,22 @@ void kasan_report_invalid_free(void *object, unsigned long ip);
> >  
> >  struct page *kasan_addr_to_page(const void *addr);
> >  
> > +depot_stack_handle_t kasan_save_stack(gfp_t flags);
> > +
> >  #if defined(CONFIG_KASAN_GENERIC) && \
> >  	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
> >  void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
> >  void quarantine_reduce(void);
> >  void quarantine_remove_cache(struct kmem_cache *cache);
> > +struct kasan_track *kasan_get_aux_stack(struct kasan_alloc_meta *alloc_info,
> > +			u8 idx);
> >  #else
> >  static inline void quarantine_put(struct kasan_free_meta *info,
> >  				struct kmem_cache *cache) { }
> >  static inline void quarantine_reduce(void) { }
> >  static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
> > +static inline struct kasan_track *kasan_get_aux_stack(
> > +			struct kasan_alloc_meta *alloc_info, u8 idx) { return NULL; }
> >  #endif
> >  
> >  #ifdef CONFIG_KASAN_SW_TAGS
> > diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> > index 80f23c9da6b0..f16a1a210815 100644
> > --- a/mm/kasan/report.c
> > +++ b/mm/kasan/report.c
> > @@ -105,9 +105,13 @@ static void end_report(unsigned long *flags)
> >  	kasan_enable_current();
> >  }
> >  
> > -static void print_track(struct kasan_track *track, const char *prefix)
> > +static void print_track(struct kasan_track *track, const char *prefix,
> > +						bool is_callrcu)
> >  {
> > -	pr_err("%s by task %u:\n", prefix, track->pid);
> > +	if (is_callrcu)
> > +		pr_err("%s:\n", prefix);
> > +	else
> > +		pr_err("%s by task %u:\n", prefix, track->pid);
> >  	if (track->stack) {
> >  		unsigned long *entries;
> >  		unsigned int nr_entries;
> > @@ -187,11 +191,20 @@ static void describe_object(struct kmem_cache *cache, void *object,
> >  	if (cache->flags & SLAB_KASAN) {
> >  		struct kasan_track *free_track;
> >  
> > -		print_track(&alloc_info->alloc_track, "Allocated");
> > +		print_track(&alloc_info->alloc_track, "Allocated", false);
> >  		pr_err("\n");
> >  		free_track = kasan_get_free_track(cache, object, tag);
> > -		print_track(free_track, "Freed");
> > +		print_track(free_track, "Freed", false);
> >  		pr_err("\n");
> > +
> > +		if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> > +			free_track = kasan_get_aux_stack(alloc_info, 0);
> > +			print_track(free_track, "First call_rcu() call stack", true);
> > +			pr_err("\n");
> > +			free_track = kasan_get_aux_stack(alloc_info, 1);
> > +			print_track(free_track, "Last call_rcu() call stack", true);
> > +			pr_err("\n");
> > +		}
> >  	}
> >  
> >  	describe_object_addr(cache, object, addr);
> > -- 
> I> 2.18.0