Re: [PATCH v2 14/19] lib/stackdepot, kasan: add flags to __stack_depot_save and rename

Marco Elver
2023-09-15T20:32:44Z

On Wed, 13 Sept 2023 at 19:17, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Change the bool can_alloc argument of __stack_depot_save to a
> u32 argument that accepts a set of flags.
>
> The following patch will add another flag to stack_depot_save_flags
> besides the existing STACK_DEPOT_FLAG_CAN_ALLOC.
>
> Also rename the function to stack_depot_save_flags, as __stack_depot_save
> is a cryptic name,
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Changes v1->v2:
> - This is a new patch.
> ---
> include/linux/stackdepot.h | 36 +++++++++++++++++++++++++-----------
> lib/stackdepot.c | 16 +++++++++++-----
> mm/kasan/common.c | 7 ++++---
> mm/kasan/generic.c | 9 +++++----
> mm/kasan/kasan.h | 2 +-
> mm/kasan/tags.c | 3 ++-
> 6 files changed, 48 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index e58306783d8e..0b262e14144e 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -32,6 +32,17 @@ typedef u32 depot_stack_handle_t;
> */
> #define STACK_DEPOT_EXTRA_BITS 5
>
> +typedef u32 depot_flags_t;
> +
> +/*
> + * Flags that can be passed to stack_depot_save_flags(); see the comment next
> + * to its declaration for more details.
> + */
> +#define STACK_DEPOT_FLAG_CAN_ALLOC ((depot_flags_t)0x0001)
> +
> +#define STACK_DEPOT_FLAGS_NUM 1
> +#define STACK_DEPOT_FLAGS_MASK ((depot_flags_t)((1 << STACK_DEPOT_FLAGS_NUM) - 1))
> +
> /*
> * Using stack depot requires its initialization, which can be done in 3 ways:
> *
> @@ -69,31 +80,34 @@ static inline int stack_depot_early_init(void) { return 0; }
> #endif
>
> /**
> - * __stack_depot_save - Save a stack trace to stack depot
> + * stack_depot_save_flags - Save a stack trace to stack depot
> *
> * @entries: Pointer to the stack trace
> * @nr_entries: Number of frames in the stack
> * @alloc_flags: Allocation GFP flags
> - * @can_alloc: Allocate stack pools (increased chance of failure if false)
> + * @depot_flags: Stack depot flags
> + *
> + * Saves a stack trace from @entries array of size @nr_entries.
> *
> - * Saves a stack trace from @entries array of size @nr_entries. If @can_alloc is
> - * %true, stack depot can replenish the stack pools in case no space is left
> - * (allocates using GFP flags of @alloc_flags). If @can_alloc is %false, avoids
> - * any allocations and fails if no space is left to store the stack trace.
> + * If STACK_DEPOT_FLAG_CAN_ALLOC is set in @depot_flags, stack depot can
> + * replenish the stack pools in case no space is left (allocates using GFP
> + * flags of @alloc_flags). Otherwise, stack depot avoids any allocations and
> + * fails if no space is left to store the stack trace.
> *
> * If the provided stack trace comes from the interrupt context, only the part
> * up to the interrupt entry is saved.
> *
> - * Context: Any context, but setting @can_alloc to %false is required if
> + * Context: Any context, but setting STACK_DEPOT_FLAG_CAN_ALLOC is required if
> * alloc_pages() cannot be used from the current context. Currently
> * this is the case for contexts where neither %GFP_ATOMIC nor
> * %GFP_NOWAIT can be used (NMI, raw_spin_lock).
> *
> * Return: Handle of the stack struct stored in depot, 0 on failure
> */
> -depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> - unsigned int nr_entries,
> - gfp_t gfp_flags, bool can_alloc);
> +depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
> + unsigned int nr_entries,
> + gfp_t gfp_flags,
> + depot_flags_t depot_flags);
>
> /**
> * stack_depot_save - Save a stack trace to stack depot
> @@ -103,7 +117,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> * @alloc_flags: Allocation GFP flags
> *
> * Context: Contexts where allocations via alloc_pages() are allowed.
> - * See __stack_depot_save() for more details.
> + * See stack_depot_save_flags() for more details.
> *
> * Return: Handle of the stack trace stored in depot, 0 on failure
> */
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 1b08897ebd2b..e5121225f124 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -438,19 +438,24 @@ static inline struct stack_record *find_stack(struct list_head *bucket,
> return NULL;
> }
>
> -depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> - unsigned int nr_entries,
> - gfp_t alloc_flags, bool can_alloc)
> +depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
> + unsigned int nr_entries,
> + gfp_t alloc_flags,
> + depot_flags_t depot_flags)
> {
> struct list_head *bucket;
> struct stack_record *found = NULL;
> depot_stack_handle_t handle = 0;
> struct page *page = NULL;
> void *prealloc = NULL;
> + bool can_alloc = depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC;
> bool need_alloc = false;
> unsigned long flags;
> u32 hash;
>
> + if (depot_flags & ~STACK_DEPOT_FLAGS_MASK)
> + return 0;
> +

Shouldn't this be a WARN due to invalid flags?

> /*
> * If this stack trace is from an interrupt, including anything before
> * interrupt entry usually leads to unbounded stack depot growth.
> @@ -529,13 +534,14 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
> handle = found->handle.handle;
> return handle;
> }
> -EXPORT_SYMBOL_GPL(__stack_depot_save);
> +EXPORT_SYMBOL_GPL(stack_depot_save_flags);
>
> depot_stack_handle_t stack_depot_save(unsigned long *entries,
> unsigned int nr_entries,
> gfp_t alloc_flags)
> {
> - return __stack_depot_save(entries, nr_entries, alloc_flags, true);
> + return stack_depot_save_flags(entries, nr_entries, alloc_flags,
> + STACK_DEPOT_FLAG_CAN_ALLOC);
> }
> EXPORT_SYMBOL_GPL(stack_depot_save);
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 256930da578a..825a0240ec02 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -22,6 +22,7 @@
> #include <linux/sched.h>
> #include <linux/sched/task_stack.h>
> #include <linux/slab.h>
> +#include <linux/stackdepot.h>
> #include <linux/stacktrace.h>
> #include <linux/string.h>
> #include <linux/types.h>
> @@ -37,19 +38,19 @@ struct slab *kasan_addr_to_slab(const void *addr)
> return NULL;
> }
>
> -depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
> +depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags)
> {
> unsigned long entries[KASAN_STACK_DEPTH];
> unsigned int nr_entries;
>
> nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> - return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> + return stack_depot_save_flags(entries, nr_entries, flags, depot_flags);
> }
>
> void kasan_set_track(struct kasan_track *track, gfp_t flags)
> {
> track->pid = current->pid;
> - track->stack = kasan_save_stack(flags, true);
> + track->stack = kasan_save_stack(flags, STACK_DEPOT_FLAG_CAN_ALLOC);
> }
>
> #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index 4d837ab83f08..5d168c9afb32 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -25,6 +25,7 @@
> #include <linux/sched.h>
> #include <linux/sched/task_stack.h>
> #include <linux/slab.h>
> +#include <linux/stackdepot.h>
> #include <linux/stacktrace.h>
> #include <linux/string.h>
> #include <linux/types.h>
> @@ -472,7 +473,7 @@ size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
> sizeof(struct kasan_free_meta) : 0);
> }
>
> -static void __kasan_record_aux_stack(void *addr, bool can_alloc)
> +static void __kasan_record_aux_stack(void *addr, depot_flags_t depot_flags)
> {
> struct slab *slab = kasan_addr_to_slab(addr);
> struct kmem_cache *cache;
> @@ -489,17 +490,17 @@ static void __kasan_record_aux_stack(void *addr, bool can_alloc)
> return;
>
> alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0];
> - alloc_meta->aux_stack[0] = kasan_save_stack(0, can_alloc);
> + alloc_meta->aux_stack[0] = kasan_save_stack(0, depot_flags);
> }
>
> void kasan_record_aux_stack(void *addr)
> {
> - return __kasan_record_aux_stack(addr, true);
> + return __kasan_record_aux_stack(addr, STACK_DEPOT_FLAG_CAN_ALLOC);
> }
>
> void kasan_record_aux_stack_noalloc(void *addr)
> {
> - return __kasan_record_aux_stack(addr, false);
> + return __kasan_record_aux_stack(addr, 0);
> }
>
> void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index f70e3d7a602e..de3206e11888 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -370,7 +370,7 @@ static inline void kasan_init_cache_meta(struct kmem_cache *cache, unsigned int
> static inline void kasan_init_object_meta(struct kmem_cache *cache, const void *object) { }
> #endif
>
> -depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc);
> +depot_stack_handle_t kasan_save_stack(gfp_t flags, depot_flags_t depot_flags);
> void kasan_set_track(struct kasan_track *track, gfp_t flags);
> void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);
> void kasan_save_free_info(struct kmem_cache *cache, void *object);
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index 7dcfe341d48e..4fd32121b0fd 100644
> --- a/mm/kasan/tags.c
> +++ b/mm/kasan/tags.c
> @@ -13,6 +13,7 @@
> #include <linux/memblock.h>
> #include <linux/memory.h>
> #include <linux/mm.h>
> +#include <linux/stackdepot.h>
> #include <linux/static_key.h>
> #include <linux/string.h>
> #include <linux/types.h>
> @@ -101,7 +102,7 @@ static void save_stack_info(struct kmem_cache *cache, void *object,
> struct kasan_stack_ring_entry *entry;
> void *old_ptr;
>
> - stack = kasan_save_stack(gfp_flags, true);
> + stack = kasan_save_stack(gfp_flags, STACK_DEPOT_FLAG_CAN_ALLOC);
>
> /*
> * Prevent save_stack_info() from modifying stack ring
> --
> 2.25.1
>