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Date: Fri, 8 Jul 2016 12:36:20 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: Andrey Konovalov <adech.fo@...il.com>,
Christoph Lameter <cl@...ux.com>,
Dmitriy Vyukov <dvyukov@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Steven Rostedt <rostedt@...dmis.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Joonsoo Kim <js1304@...il.com>,
Kostya Serebryany <kcc@...gle.com>,
Kuthonuzo Luruo <kuthonuzo.luruo@....com>,
kasan-dev <kasan-dev@...glegroups.com>,
Linux Memory Management List <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] mm, kasan: switch SLUB to stackdepot, enable memory
quarantine for SLUB
On Tue, Jun 28, 2016 at 6:51 PM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
>
>
> On 06/22/2016 08:43 PM, Alexander Potapenko wrote:
>> For KASAN builds:
>> - switch SLUB allocator to using stackdepot instead of storing the
>> allocation/deallocation stacks in the objects;
>> - change the freelist hook so that parts of the freelist can be put
>> into the quarantine.
>>
>> Signed-off-by: Alexander Potapenko <glider@...gle.com>
>> ---
>> v5: - addressed comments by Andrey Ryabinin:
>> - don't define SLAB_RED_ZONE, SLAB_POISON, SLAB_STORE_USER to 0
>
> check_pad_bytes() needs fixing. It should take into accout kasan metadata size.
Done.
>
>> - account for left redzone size when SLAB_RED_ZONE is used
>> - incidentally moved the implementations of nearest_obj() to mm/sl[au]b.c
>> v4: - addressed comments by Andrey Ryabinin:
>> - don't set slub_debug by default for everyone;
>> - introduce the ___cache_free() helper function.
>> v3: - addressed comments by Andrey Ryabinin:
>> - replaced KMALLOC_MAX_CACHE_SIZE with KMALLOC_MAX_SIZE in
>> kasan_cache_create();
>> - for caches with SLAB_KASAN flag set, their alloc_meta_offset and
>> free_meta_offset are always valid.
>> v2: - incorporated kbuild fixes by Andrew Morton
>> ---
>> include/linux/slab_def.h | 11 -------
>> include/linux/slub_def.h | 15 +++-------
>> lib/Kconfig.kasan | 4 +--
>> mm/kasan/Makefile | 3 +-
>> mm/kasan/kasan.c | 61 ++++++++++++++++++++------------------
>> mm/kasan/kasan.h | 2 +-
>> mm/kasan/report.c | 8 ++---
>> mm/slab.c | 11 +++++++
>> mm/slab.h | 9 ++++++
>> mm/slub.c | 76 +++++++++++++++++++++++++++++++++++++++---------
>> 10 files changed, 126 insertions(+), 74 deletions(-)
>>
>> diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
>> index 8694f7a..a20e11c 100644
>> --- a/include/linux/slab_def.h
>> +++ b/include/linux/slab_def.h
>> @@ -87,15 +87,4 @@ struct kmem_cache {
>> struct kmem_cache_node *node[MAX_NUMNODES];
>> };
>>
>> -static inline void *nearest_obj(struct kmem_cache *cache, struct page *page,
>> - void *x) {
>> - void *object = x - (x - page->s_mem) % cache->size;
>> - void *last_object = page->s_mem + (cache->num - 1) * cache->size;
>> -
>> - if (unlikely(object > last_object))
>> - return last_object;
>> - else
>> - return object;
>> -}
>> -
>> #endif /* _LINUX_SLAB_DEF_H */
>> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
>> index d1faa01..da80e7f 100644
>> --- a/include/linux/slub_def.h
>> +++ b/include/linux/slub_def.h
>> @@ -99,6 +99,10 @@ struct kmem_cache {
>> */
>> int remote_node_defrag_ratio;
>> #endif
>> +#ifdef CONFIG_KASAN
>> + struct kasan_cache kasan_info;
>> +#endif
>> +
>> struct kmem_cache_node *node[MAX_NUMNODES];
>> };
>>
>> @@ -114,15 +118,4 @@ static inline void sysfs_slab_remove(struct kmem_cache *s)
>> void object_err(struct kmem_cache *s, struct page *page,
>> u8 *object, char *reason);
>>
>> -static inline void *nearest_obj(struct kmem_cache *cache, struct page *page,
>> - void *x) {
>> - void *object = x - (x - page_address(page)) % cache->size;
>> - void *last_object = page_address(page) +
>> - (page->objects - 1) * cache->size;
>> - if (unlikely(object > last_object))
>> - return last_object;
>> - else
>> - return object;
>> -}
>> -
>> #endif /* _LINUX_SLUB_DEF_H */
>> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
>> index 67d8c68..bd38aab 100644
>> --- a/lib/Kconfig.kasan
>> +++ b/lib/Kconfig.kasan
>> @@ -5,9 +5,9 @@ if HAVE_ARCH_KASAN
>>
>> config KASAN
>> bool "KASan: runtime memory debugger"
>> - depends on SLUB_DEBUG || (SLAB && !DEBUG_SLAB)
>> + depends on SLUB || (SLAB && !DEBUG_SLAB)
>> select CONSTRUCTORS
>> - select STACKDEPOT if SLAB
>> + select STACKDEPOT
>> help
>> Enables kernel address sanitizer - runtime memory debugger,
>> designed to find out-of-bounds accesses and use-after-free bugs.
>> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
>> index 1548749..2976a9e 100644
>> --- a/mm/kasan/Makefile
>> +++ b/mm/kasan/Makefile
>> @@ -7,5 +7,4 @@ CFLAGS_REMOVE_kasan.o = -pg
>> # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
>> CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
>>
>> -obj-y := kasan.o report.o kasan_init.o
>> -obj-$(CONFIG_SLAB) += quarantine.o
>> +obj-y := kasan.o report.o kasan_init.o quarantine.o
>> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
>> index 28439ac..3883e22 100644
>> --- a/mm/kasan/kasan.c
>> +++ b/mm/kasan/kasan.c
>> @@ -351,7 +351,6 @@ void kasan_free_pages(struct page *page, unsigned int order)
>> KASAN_FREE_PAGE);
>> }
>>
>> -#ifdef CONFIG_SLAB
>> /*
>> * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
>> * For larger allocations larger redzones are used.
>> @@ -373,16 +372,12 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size,
>> unsigned long *flags)
>> {
>> int redzone_adjust;
>> - /* Make sure the adjusted size is still less than
>> - * KMALLOC_MAX_CACHE_SIZE.
>> - * TODO: this check is only useful for SLAB, but not SLUB. We'll need
>> - * to skip it for SLUB when it starts using kasan_cache_create().
>> - */
>> - if (*size > KMALLOC_MAX_CACHE_SIZE -
>> - sizeof(struct kasan_alloc_meta) -
>> - sizeof(struct kasan_free_meta))
>> - return;
>> +#ifdef CONFIG_SLAB
>> + int orig_size = *size;
>> +#endif
>> +
>> *flags |= SLAB_KASAN;
>> +
>> /* Add alloc meta. */
>> cache->kasan_info.alloc_meta_offset = *size;
>> *size += sizeof(struct kasan_alloc_meta);
>> @@ -392,17 +387,35 @@ void kasan_cache_create(struct kmem_cache *cache, size_t *size,
>> cache->object_size < sizeof(struct kasan_free_meta)) {
>> cache->kasan_info.free_meta_offset = *size;
>> *size += sizeof(struct kasan_free_meta);
>> + } else {
>> + cache->kasan_info.free_meta_offset = 0;
>
> Why is that required now?
Because we want to store the free metadata in the object when it's possible.
>
>> }
>> redzone_adjust = optimal_redzone(cache->object_size) -
>> (*size - cache->object_size);
>> +
>> if (redzone_adjust > 0)
>> *size += redzone_adjust;
>> - *size = min(KMALLOC_MAX_CACHE_SIZE,
>> +
>> +#ifdef CONFIG_SLAB
>> + *size = min(KMALLOC_MAX_SIZE,
>> max(*size,
>> cache->object_size +
>> optimal_redzone(cache->object_size)));
>> -}
>> + /*
>> + * If the metadata doesn't fit, disable KASAN at all.
>> + */
>> + if (*size <= cache->kasan_info.alloc_meta_offset ||
>> + *size <= cache->kasan_info.free_meta_offset) {
>> + *flags &= ~SLAB_KASAN;
>
> Why we change that flag back and forth instead of setting it once?
Agreed. I've fixed this.
>> + *size = orig_size;
>> + }
>> +#else
>> + *size = max(*size,
>> + cache->object_size +
>> + optimal_redzone(cache->object_size));
>> +
>> #endif
>> +}
>>
>> void kasan_cache_shrink(struct kmem_cache *cache)
>> {
>> @@ -431,16 +444,13 @@ void kasan_poison_object_data(struct kmem_cache *cache, void *object)
>> kasan_poison_shadow(object,
>> round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
>> KASAN_KMALLOC_REDZONE);
>> -#ifdef CONFIG_SLAB
>> if (cache->flags & SLAB_KASAN) {
>> struct kasan_alloc_meta *alloc_info =
>> get_alloc_info(cache, object);
>> alloc_info->state = KASAN_STATE_INIT;
>> }
>> -#endif
>> }
>>
>> -#ifdef CONFIG_SLAB
>> static inline int in_irqentry_text(unsigned long ptr)
>> {
>> return (ptr >= (unsigned long)&__irqentry_text_start &&
>> @@ -501,7 +511,6 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
>> BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
>> return (void *)object + cache->kasan_info.free_meta_offset;
>> }
>> -#endif
>>
>> void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
>> {
>> @@ -522,16 +531,16 @@ void kasan_poison_slab_free(struct kmem_cache *cache, void *object)
>>
>> bool kasan_slab_free(struct kmem_cache *cache, void *object)
>> {
>> -#ifdef CONFIG_SLAB
>> /* RCU slabs could be legally used after free within the RCU period */
>> if (unlikely(cache->flags & SLAB_DESTROY_BY_RCU))
>> return false;
>>
>> if (likely(cache->flags & SLAB_KASAN)) {
>> - struct kasan_alloc_meta *alloc_info =
>> - get_alloc_info(cache, object);
>> - struct kasan_free_meta *free_info =
>> - get_free_info(cache, object);
>> + struct kasan_alloc_meta *alloc_info;
>> + struct kasan_free_meta *free_info;
>> +
>> + alloc_info = get_alloc_info(cache, object);
>> + free_info = get_free_info(cache, object);
>>
>> switch (alloc_info->state) {
>> case KASAN_STATE_ALLOC:
>> @@ -550,10 +559,6 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)
>> }
>> }
>> return false;
>> -#else
>> - kasan_poison_slab_free(cache, object);
>> - return false;
>> -#endif
>> }
>>
>> void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
>> @@ -568,6 +573,9 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
>> if (unlikely(object == NULL))
>> return;
>>
>> + if (!(cache->flags & SLAB_KASAN))
>> + return;
>> +
>
> This hunk is superfluous and wrong.
Can you please elaborate?
Do you mean we don't need to check for SLAB_KASAN here, or that we
don't need SLAB_KASAN at all?
>
>> redzone_start = round_up((unsigned long)(object + size),
>> KASAN_SHADOW_SCALE_SIZE);
>> redzone_end = round_up((unsigned long)object + cache->object_size,
>> @@ -576,16 +584,13 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
>> kasan_unpoison_shadow(object, size);
>> kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
>> KASAN_KMALLOC_REDZONE);
>> -#ifdef CONFIG_SLAB
>> if (cache->flags & SLAB_KASAN) {
>> struct kasan_alloc_meta *alloc_info =
>> get_alloc_info(cache, object);
>> -
>
> Keep the space please.
Done.
>
>> alloc_info->state = KASAN_STATE_ALLOC;
>> alloc_info->alloc_size = size;
>> set_track(&alloc_info->track, flags);
>> }
>> -#endif
>> }
>> EXPORT_SYMBOL(kasan_kmalloc);
>>
>> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
>> index fb87923..8c75953 100644
>> --- a/mm/kasan/kasan.h
>> +++ b/mm/kasan/kasan.h
>> @@ -110,7 +110,7 @@ static inline bool kasan_report_enabled(void)
>> void kasan_report(unsigned long addr, size_t size,
>> bool is_write, unsigned long ip);
>>
>> -#ifdef CONFIG_SLAB
>> +#if 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);
>> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
>> index b3c122d..861b977 100644
>> --- a/mm/kasan/report.c
>> +++ b/mm/kasan/report.c
>> @@ -116,7 +116,6 @@ static inline bool init_task_stack_addr(const void *addr)
>> sizeof(init_thread_union.stack));
>> }
>>
>> -#ifdef CONFIG_SLAB
>> static void print_track(struct kasan_track *track)
>> {
>> pr_err("PID = %u\n", track->pid);
>> @@ -130,8 +129,8 @@ static void print_track(struct kasan_track *track)
>> }
>> }
>>
>> -static void object_err(struct kmem_cache *cache, struct page *page,
>> - void *object, char *unused_reason)
>> +static void kasan_object_err(struct kmem_cache *cache, struct page *page,
>> + void *object, char *unused_reason)
>> {
>> struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
>> struct kasan_free_meta *free_info;
>> @@ -162,7 +161,6 @@ static void object_err(struct kmem_cache *cache, struct page *page,
>> break;
>> }
>> }
>> -#endif
>>
>> static void print_address_description(struct kasan_access_info *info)
>> {
>> @@ -177,7 +175,7 @@ static void print_address_description(struct kasan_access_info *info)
>> struct kmem_cache *cache = page->slab_cache;
>> object = nearest_obj(cache, page,
>> (void *)info->access_addr);
>> - object_err(cache, page, object,
>> + kasan_object_err(cache, page, object,
>> "kasan: bad access detected");
>> return;
>> }
>> diff --git a/mm/slab.c b/mm/slab.c
>> index cc8bbc1..e944171 100644
>> --- a/mm/slab.c
>> +++ b/mm/slab.c
>> @@ -4506,3 +4506,14 @@ size_t ksize(const void *objp)
>> return size;
>> }
>> EXPORT_SYMBOL(ksize);
>> +
>> +void *nearest_obj(struct kmem_cache *cache, struct page *page, void *x)
>> +{
>> + void *object = x - (x - page->s_mem) % cache->size;
>> + void *last_object = page->s_mem + (cache->num - 1) * cache->size;
>> +
>> + if (unlikely(object > last_object))
>> + return last_object;
>> + else
>> + return object;
>> +}
>
> This should be in header. Don't bloat CONFIG_KASAN=n kernels.
Ok, I've moved it back.
>> diff --git a/mm/slab.h b/mm/slab.h
>> index dedb1a9..52edd1e 100644
>> --- a/mm/slab.h
>> +++ b/mm/slab.h
>> @@ -366,6 +366,8 @@ static inline size_t slab_ksize(const struct kmem_cache *s)
>> if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
>> return s->object_size;
>> # endif
>> + if (s->flags & SLAB_KASAN)
>> + return s->object_size;
>> /*
>> * If we have the need to store the freelist pointer
>> * back there or track user information then we can
>> @@ -462,6 +464,13 @@ void *slab_next(struct seq_file *m, void *p, loff_t *pos);
>> void slab_stop(struct seq_file *m, void *p);
>> int memcg_slab_show(struct seq_file *m, void *p);
>>
>> +void *nearest_obj(struct kmem_cache *cache, struct page *page, void *x);
>> +
>> void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr);
>> +#if defined(CONFIG_SLUB)
>> +void do_slab_free(struct kmem_cache *s,
>> + struct page *page, void *head, void *tail,
>> + int cnt, unsigned long addr);
>> +#endif
>>
>> #endif /* MM_SLAB_H */
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 825ff45..3ef06e3 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -191,7 +191,11 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
>> #define MAX_OBJS_PER_PAGE 32767 /* since page.objects is u15 */
>>
>> /* Internal SLUB flags */
>> +#ifndef CONFIG_KASAN
>> #define __OBJECT_POISON 0x80000000UL /* Poison object */
>> +#else
>> +#define __OBJECT_POISON 0x00000000UL /* Disable object poisoning */
>
> Again, why? It should just work.
Yeah, it appears to work now. Removed these bits.
>> +#endif
>> #define __CMPXCHG_DOUBLE 0x40000000UL /* Use cmpxchg_double */
>>
>> #ifdef CONFIG_SMP
>> @@ -454,8 +458,6 @@ static inline void *restore_red_left(struct kmem_cache *s, void *p)
>> */
>> #if defined(CONFIG_SLUB_DEBUG_ON)
>> static int slub_debug = DEBUG_DEFAULT_FLAGS;
>> -#elif defined(CONFIG_KASAN)
>> -static int slub_debug = SLAB_STORE_USER;
>> #else
>> static int slub_debug;
>> #endif
>> @@ -1322,7 +1324,7 @@ static inline void kfree_hook(const void *x)
>> kasan_kfree_large(x);
>> }
>>
>> -static inline void slab_free_hook(struct kmem_cache *s, void *x)
>> +static inline bool slab_free_hook(struct kmem_cache *s, void *x)
>> {
>> kmemleak_free_recursive(x, s->flags);
>>
>> @@ -1344,11 +1346,11 @@ static inline void slab_free_hook(struct kmem_cache *s, void *x)
>> if (!(s->flags & SLAB_DEBUG_OBJECTS))
>> debug_check_no_obj_freed(x, s->object_size);
>>
>> - kasan_slab_free(s, x);
>> + return kasan_slab_free(s, x);
>> }
>>
>> static inline void slab_free_freelist_hook(struct kmem_cache *s,
>> - void *head, void *tail)
>> + void **head, void **tail, int *cnt)
>> {
>> /*
>> * Compiler cannot detect this function can be removed if slab_free_hook()
>> @@ -1360,13 +1362,27 @@ static inline void slab_free_freelist_hook(struct kmem_cache *s,
>> defined(CONFIG_DEBUG_OBJECTS_FREE) || \
>> defined(CONFIG_KASAN)
>>
>> - void *object = head;
>> - void *tail_obj = tail ? : head;
>> + void *object = *head, *prev = NULL, *next = NULL;
>> + void *tail_obj = *tail ? : *head;
>> + bool skip = false;
>>
>> do {
>> - slab_free_hook(s, object);
>> - } while ((object != tail_obj) &&
>> - (object = get_freepointer(s, object)));
>> + skip = slab_free_hook(s, object);
>> + next = (object != tail_obj) ?
>> + get_freepointer(s, object) : NULL;
>> + if (skip) {
>> + if (!prev)
>> + *head = next;
>> + else
>> + set_freepointer(s, prev, next);
>> + if (object == tail_obj)
>> + *tail = prev;
>> + (*cnt)--;
>> + } else {
>> + prev = object;
>> + }
>> + object = next;
>> + } while (next);
>> #endif
>> }
>>
>> @@ -2772,12 +2788,22 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
>> void *head, void *tail, int cnt,
>> unsigned long addr)
>> {
>> + void *free_head = head, *free_tail = tail;
>> +
>> + slab_free_freelist_hook(s, &free_head, &free_tail, &cnt);
>> + /* slab_free_freelist_hook() could have emptied the freelist. */
>> + if (cnt == 0)
>> + return;
>
> I suppose that we can do something like following, instead of that mess in slab_free_freelist_hook() above
>
> slab_free_freelist_hook(s, &free_head, &free_tail);
> if (s->flags & SLAB_KASAN && s->flags & SLAB_DESTROY_BY_RCU)
Did you mean "&& !(s->flags & SLAB_DESTROY_BY_RCU)" ?
> return;
Yes, my code is overly complicated given that kasan_slab_free() should
actually return the same value for every element of the list.
(do you think it makes sense to check that?)
I can safely remove those freelist manipulations.
>
>
>> + do_slab_free(s, page, free_head, free_tail, cnt, addr);
>> +}
>> +
>> +__always_inline void do_slab_free(struct kmem_cache *s,
>
> static
Done.
>> + struct page *page, void *head, void *tail,
>> + int cnt, unsigned long addr)
>> +{
>> void *tail_obj = tail ? : head;
>> struct kmem_cache_cpu *c;
>> unsigned long tid;
>> -
>> - slab_free_freelist_hook(s, head, tail);
>> -
>> redo:
>> /*
>> * Determine the currently cpus per cpu slab.
>> @@ -2811,6 +2837,12 @@ redo:
>>
>> }
>>
>> +/* Helper function to be used from qlink_free() in mm/kasan/quarantine.c */
>
> We have grep to locate all call sites. Unlike comments like this, grep results always uptodate.
Removed the comment.
>> +void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
>> +{
>> + do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr);
>> +}
>> +
>> void kmem_cache_free(struct kmem_cache *s, void *x)
>> {
>> s = cache_from_obj(s, x);
>> @@ -3252,7 +3284,7 @@ static void set_min_partial(struct kmem_cache *s, unsigned long min)
>> static int calculate_sizes(struct kmem_cache *s, int forced_order)
>> {
>> unsigned long flags = s->flags;
>> - unsigned long size = s->object_size;
>> + size_t size = s->object_size;
>> int order;
>>
>> /*
>> @@ -3311,7 +3343,10 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
>> * the object.
>> */
>> size += 2 * sizeof(struct track);
>> +#endif
>>
>> + kasan_cache_create(s, &size, &s->flags);
>> +#ifdef CONFIG_SLUB_DEBUG
>> if (flags & SLAB_RED_ZONE) {
>> /*
>> * Add some empty padding so that we can catch
>> @@ -5585,3 +5620,16 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
>> return -EIO;
>> }
>> #endif /* CONFIG_SLABINFO */
>> +
>> +void *nearest_obj(struct kmem_cache *cache, struct page *page,
>> + void *x) {
>> + void *object = x - (x - page_address(page)) % cache->size;
>> + void *last_object = page_address(page) +
>> + (page->objects - 1) * cache->size;
>> + void *result = (unlikely(object > last_object)) ? last_object : object;
>> +
>> + if (cache->flags & SLAB_RED_ZONE)
>> + return (void *)((char *)result + cache->red_left_pad);
>
> red_left_pad is zero when SLAB_RED_ZONE is unset, so if/else is not needed here.
Yet every use of red_left_pad in the codebase is preceded with a
SLAB_RED_ZONE check.
I find this logical.
> And it can be moved back to header now.
Done.
> Also, you don't need (void *) cast.
Done.
>
>> + else
>> + return result;
>> +}
>>
>
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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