Re: [PATCH v4 1/4] rcu/kasan: record and print call_rcu() call stack

Andrey Konovalov
2020-05-19T14:52:43Z

On Tue, May 19, 2020 at 4:24 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> This feature will record the last two call_rcu() call stacks and
> prints up to 2 call_rcu() call stacks in KASAN report.
>
> When call_rcu() is called, we store the call_rcu() call stack into
> slub alloc meta-data, so that the KASAN report can print rcu stack.
>
> [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@mediatek.com>
> Suggested-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> ---
> include/linux/kasan.h | 2 ++
> kernel/rcu/tree.c | 2 ++
> lib/Kconfig.kasan | 2 ++
> mm/kasan/common.c | 4 ++--
> mm/kasan/generic.c | 19 +++++++++++++++++++
> mm/kasan/kasan.h | 10 ++++++++++
> mm/kasan/report.c | 24 ++++++++++++++++++++++++
> 7 files changed, 61 insertions(+), 2 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..36a4ff7f320b 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"
> @@ -2668,6 +2669,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func)
> head->func = func;
> head->next = NULL;
> local_irq_save(flags);
> + kasan_record_aux_stack(head);
> rdp = this_cpu_ptr(&rcu_data);
>
> /* Add the callback to our list. */
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index 81f5464ea9e1..4e83cf6e3caa 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).
> + In generic mode KASAN prints the last two call_rcu() call stacks in
> + reports.

I don't think we need this here, mentioning this in the documentation is fine.

>
> 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..3372bdcaf92a 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -325,3 +325,22 @@ 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);
> +
> + /* record the last two call_rcu() call stacks */
> + alloc_info->aux_stack[1] = alloc_info->aux_stack[0];
> + alloc_info->aux_stack[0] = kasan_save_stack(GFP_NOWAIT);
> +}
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index e8f37199d885..a7391bc83070 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -104,7 +104,15 @@ struct kasan_track {
>
> 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 struct kasan_free_meta.
> + */
> + depot_stack_handle_t aux_stack[2];
> +#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;
> @@ -159,6 +167,8 @@ 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);
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 80f23c9da6b0..6f8f2bf8f53b 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -179,6 +179,17 @@ static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
> return &alloc_meta->free_track[i];
> }
>
> +#ifdef CONFIG_KASAN_GENERIC
> +static void print_stack(depot_stack_handle_t stack)

Let's put this function just before print_track() and reuse there.

> +{
> + unsigned long *entries;
> + unsigned int nr_entries;
> +
> + nr_entries = stack_depot_fetch(stack, &entries);
> + stack_trace_print(entries, nr_entries, 0);
> +}
> +#endif
> +
> static void describe_object(struct kmem_cache *cache, void *object,
> const void *addr, u8 tag)
> {
> @@ -192,6 +203,19 @@ static void describe_object(struct kmem_cache *cache, void *object,
> free_track = kasan_get_free_track(cache, object, tag);
> print_track(free_track, "Freed");
> pr_err("\n");
> +
> +#ifdef CONFIG_KASAN_GENERIC
> + if (alloc_info->aux_stack[0]) {
> + pr_err("Last one call_rcu() call stack:\n");

Could you change this to "Last call_rcu():\n",

> + print_stack(alloc_info->aux_stack[0]);
> + pr_err("\n");
> + }
> + if (alloc_info->aux_stack[1]) {
> + pr_err("Second to last call_rcu() call stack:\n");

and this to "Second to last call_rcu():\n"?

It's shorter, but provides the same info.

> + print_stack(alloc_info->aux_stack[1]);
> + pr_err("\n");
> + }
> +#endif
> }
>
> describe_object_addr(cache, object, addr);
> --
> 2.18.0
>
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