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3c5c3cfb9e
Patch series "kasan: support backing vmalloc space with real shadow
memory", v11.
Currently, vmalloc space is backed by the early shadow page. This means
that kasan is incompatible with VMAP_STACK.
This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's very
easy to wire up other architectures, and it appears that there is some
work-in-progress code to do this on arm64 and s390.
This has been discussed before in the context of VMAP_STACK:
- https://bugzilla.kernel.org/show_bug.cgi?id=202009
- https://lkml.org/lkml/2018/7/22/198
- https://lkml.org/lkml/2019/7/19/822
In terms of implementation details:
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=1)
This is unfortunate but given that this is a debug feature only, not the
end of the world. The benchmarks are also a stress-test for the vmalloc
subsystem: they're not indicative of an overall 2x slowdown!
This patch (of 4):
Hook into vmalloc and vmap, and dynamically allocate real shadow memory
to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc space
will not be covered by the early shadow page, but will be left unmapped.
This will require changes in arch-specific code.
This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=3D1)
This is unfortunate but given that this is a debug feature only, not the
end of the world.
The full benchmark results are:
Performance
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 662004 11404956 17.23 19144610 28.92 1.68
full_fit_alloc_test 710950 12029752 16.92 13184651 18.55 1.10
long_busy_list_alloc_test 9431875 43990172 4.66 82970178 8.80 1.89
random_size_alloc_test 5033626 23061762 4.58 47158834 9.37 2.04
fix_align_alloc_test 1252514 15276910 12.20 31266116 24.96 2.05
random_size_align_alloc_te 1648501 14578321 8.84 25560052 15.51 1.75
align_shift_alloc_test 147 830 5.65 5692 38.72 6.86
pcpu_alloc_test 80732 125520 1.55 140864 1.74 1.12
Total Cycles 119240774314 763211341128 6.40 1390338696894 11.66 1.82
Sequential, 2 cpus
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 1423150 14276550 10.03 27733022 19.49 1.94
full_fit_alloc_test 1754219 14722640 8.39 15030786 8.57 1.02
long_busy_list_alloc_test 11451858 52154973 4.55 107016027 9.34 2.05
random_size_alloc_test 5989020 26735276 4.46 68885923 11.50 2.58
fix_align_alloc_test 2050976 20166900 9.83 50491675 24.62 2.50
random_size_align_alloc_te 2858229 17971700 6.29 38730225 13.55 2.16
align_shift_alloc_test 405 6428 15.87 26253 64.82 4.08
pcpu_alloc_test 127183 151464 1.19 216263 1.70 1.43
Total Cycles 54181269392 308723699764 5.70 650772566394 12.01 2.11
fix_size_alloc_test 1420404 14289308 10.06 27790035 19.56 1.94
full_fit_alloc_test 1736145 14806234 8.53 15274301 8.80 1.03
long_busy_list_alloc_test 11404638 52270785 4.58 107550254 9.43 2.06
random_size_alloc_test 6017006 26650625 4.43 68696127 11.42 2.58
fix_align_alloc_test 2045504 20280985 9.91 50414862 24.65 2.49
random_size_align_alloc_te 2845338 17931018 6.30 38510276 13.53 2.15
align_shift_alloc_test 472 3760 7.97 9656 20.46 2.57
pcpu_alloc_test 118643 132732 1.12 146504 1.23 1.10
Total Cycles 54040011688 309102805492 5.72 651325675652 12.05 2.11
[dja@axtens.net: fixups]
Link: http://lkml.kernel.org/r/20191120052719.7201-1-dja@axtens.net
Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D202009
Link: http://lkml.kernel.org/r/20191031093909.9228-2-dja@axtens.net
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [shadow rework]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
228 lines
6.7 KiB
C
228 lines
6.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_KASAN_H
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#define _LINUX_KASAN_H
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#include <linux/types.h>
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struct kmem_cache;
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struct page;
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struct vm_struct;
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struct task_struct;
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#ifdef CONFIG_KASAN
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#include <asm/kasan.h>
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#include <asm/pgtable.h>
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extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
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extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
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extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
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extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
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extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
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int kasan_populate_early_shadow(const void *shadow_start,
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const void *shadow_end);
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static inline void *kasan_mem_to_shadow(const void *addr)
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{
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return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
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+ KASAN_SHADOW_OFFSET;
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}
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/* Enable reporting bugs after kasan_disable_current() */
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extern void kasan_enable_current(void);
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/* Disable reporting bugs for current task */
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extern void kasan_disable_current(void);
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void kasan_unpoison_shadow(const void *address, size_t size);
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void kasan_unpoison_task_stack(struct task_struct *task);
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void kasan_unpoison_stack_above_sp_to(const void *watermark);
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void kasan_alloc_pages(struct page *page, unsigned int order);
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void kasan_free_pages(struct page *page, unsigned int order);
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void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
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slab_flags_t *flags);
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void kasan_poison_slab(struct page *page);
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void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
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void kasan_poison_object_data(struct kmem_cache *cache, void *object);
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void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
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const void *object);
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void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
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gfp_t flags);
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void kasan_kfree_large(void *ptr, unsigned long ip);
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void kasan_poison_kfree(void *ptr, unsigned long ip);
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void * __must_check kasan_kmalloc(struct kmem_cache *s, const void *object,
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size_t size, gfp_t flags);
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void * __must_check kasan_krealloc(const void *object, size_t new_size,
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gfp_t flags);
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void * __must_check kasan_slab_alloc(struct kmem_cache *s, void *object,
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gfp_t flags);
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bool kasan_slab_free(struct kmem_cache *s, void *object, unsigned long ip);
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struct kasan_cache {
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int alloc_meta_offset;
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int free_meta_offset;
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};
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/*
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* These functions provide a special case to support backing module
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* allocations with real shadow memory. With KASAN vmalloc, the special
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* case is unnecessary, as the work is handled in the generic case.
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*/
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#ifndef CONFIG_KASAN_VMALLOC
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int kasan_module_alloc(void *addr, size_t size);
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void kasan_free_shadow(const struct vm_struct *vm);
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#else
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static inline int kasan_module_alloc(void *addr, size_t size) { return 0; }
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static inline void kasan_free_shadow(const struct vm_struct *vm) {}
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#endif
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int kasan_add_zero_shadow(void *start, unsigned long size);
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void kasan_remove_zero_shadow(void *start, unsigned long size);
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size_t __ksize(const void *);
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static inline void kasan_unpoison_slab(const void *ptr)
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{
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kasan_unpoison_shadow(ptr, __ksize(ptr));
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}
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size_t kasan_metadata_size(struct kmem_cache *cache);
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bool kasan_save_enable_multi_shot(void);
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void kasan_restore_multi_shot(bool enabled);
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#else /* CONFIG_KASAN */
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static inline void kasan_unpoison_shadow(const void *address, size_t size) {}
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static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
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static inline void kasan_unpoison_stack_above_sp_to(const void *watermark) {}
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static inline void kasan_enable_current(void) {}
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static inline void kasan_disable_current(void) {}
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static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
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static inline void kasan_free_pages(struct page *page, unsigned int order) {}
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static inline void kasan_cache_create(struct kmem_cache *cache,
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unsigned int *size,
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slab_flags_t *flags) {}
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static inline void kasan_poison_slab(struct page *page) {}
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static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
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void *object) {}
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static inline void kasan_poison_object_data(struct kmem_cache *cache,
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void *object) {}
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static inline void *kasan_init_slab_obj(struct kmem_cache *cache,
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const void *object)
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{
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return (void *)object;
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}
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static inline void *kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags)
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{
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return ptr;
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}
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static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
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static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
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static inline void *kasan_kmalloc(struct kmem_cache *s, const void *object,
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size_t size, gfp_t flags)
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{
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return (void *)object;
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}
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static inline void *kasan_krealloc(const void *object, size_t new_size,
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gfp_t flags)
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{
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return (void *)object;
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}
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static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
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gfp_t flags)
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{
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return object;
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}
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static inline bool kasan_slab_free(struct kmem_cache *s, void *object,
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unsigned long ip)
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{
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return false;
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}
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static inline int kasan_module_alloc(void *addr, size_t size) { return 0; }
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static inline void kasan_free_shadow(const struct vm_struct *vm) {}
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static inline int kasan_add_zero_shadow(void *start, unsigned long size)
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{
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return 0;
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}
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static inline void kasan_remove_zero_shadow(void *start,
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unsigned long size)
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{}
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static inline void kasan_unpoison_slab(const void *ptr) { }
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static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
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#endif /* CONFIG_KASAN */
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#ifdef CONFIG_KASAN_GENERIC
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#define KASAN_SHADOW_INIT 0
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void kasan_cache_shrink(struct kmem_cache *cache);
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void kasan_cache_shutdown(struct kmem_cache *cache);
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#else /* CONFIG_KASAN_GENERIC */
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static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
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static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
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#endif /* CONFIG_KASAN_GENERIC */
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#ifdef CONFIG_KASAN_SW_TAGS
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#define KASAN_SHADOW_INIT 0xFF
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void kasan_init_tags(void);
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void *kasan_reset_tag(const void *addr);
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void kasan_report(unsigned long addr, size_t size,
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bool is_write, unsigned long ip);
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#else /* CONFIG_KASAN_SW_TAGS */
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static inline void kasan_init_tags(void) { }
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static inline void *kasan_reset_tag(const void *addr)
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{
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return (void *)addr;
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}
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#endif /* CONFIG_KASAN_SW_TAGS */
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#ifdef CONFIG_KASAN_VMALLOC
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int kasan_populate_vmalloc(unsigned long requested_size,
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struct vm_struct *area);
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void kasan_poison_vmalloc(void *start, unsigned long size);
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void kasan_release_vmalloc(unsigned long start, unsigned long end,
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unsigned long free_region_start,
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unsigned long free_region_end);
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#else
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static inline int kasan_populate_vmalloc(unsigned long requested_size,
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struct vm_struct *area)
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{
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return 0;
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}
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static inline void kasan_poison_vmalloc(void *start, unsigned long size) {}
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static inline void kasan_release_vmalloc(unsigned long start,
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unsigned long end,
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unsigned long free_region_start,
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unsigned long free_region_end) {}
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#endif
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#endif /* LINUX_KASAN_H */
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