[PATCH v2 0/3] kasan: tag-based mode fixes

[PATCH v2 0/3] kasan: tag-based mode fixes

[Andrey Konovalov]

Hi Andrew,

This patchset includes an updated "kasan, arm64: use ARCH_SLAB_MINALIGN
instead of manual aligning" patch and fixes for two more issues that
were uncovered while testing with a variety of different config options
enabled.

Thanks!

Andrey Konovalov (3):
  kasan, arm64: use ARCH_SLAB_MINALIGN instead of manual aligning
  kasan: make tag based mode work with CONFIG_HARDENED_USERCOPY
  kasan: fix krealloc handling for tag-based mode

 arch/arm64/include/asm/kasan.h |  4 ++++
 include/linux/kasan.h          | 14 +++++---------
 include/linux/slab.h           |  5 +++--
 mm/kasan/common.c              | 22 ++++++++++++----------
 mm/slab.c                      |  8 ++++----
 mm/slab_common.c               |  2 +-
 mm/slub.c                      | 12 +++++++-----
 7 files changed, 36 insertions(+), 31 deletions(-)

-- 
2.20.1.415.g653613c723-goog

[PATCH v2 1/3] kasan, arm64: use ARCH_SLAB_MINALIGN instead of manual aligning

[Andrey Konovalov]

Instead of changing cache->align to be aligned to KASAN_SHADOW_SCALE_SIZE
in kasan_cache_create() we can reuse the ARCH_SLAB_MINALIGN macro.

Suggested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/include/asm/kasan.h | 4 ++++
 include/linux/slab.h           | 1 +
 mm/kasan/common.c              | 2 --
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
index b52aacd2c526..ba26150d578d 100644
--- a/arch/arm64/include/asm/kasan.h
+++ b/arch/arm64/include/asm/kasan.h
@@ -36,6 +36,10 @@
 #define KASAN_SHADOW_OFFSET     (KASAN_SHADOW_END - (1ULL << \
 					(64 - KASAN_SHADOW_SCALE_SHIFT)))
 
+#ifdef CONFIG_KASAN_SW_TAGS
+#define ARCH_SLAB_MINALIGN	(1ULL << KASAN_SHADOW_SCALE_SHIFT)
+#endif
+
 void kasan_init(void);
 void kasan_copy_shadow(pgd_t *pgdir);
 asmlinkage void kasan_early_init(void);
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 11b45f7ae405..d87f913ab4e8 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -16,6 +16,7 @@
 #include <linux/overflow.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/kasan.h>
 
 
 /*
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 03d5d1374ca7..44390392d4c9 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -298,8 +298,6 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
 		return;
 	}
 
-	cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE);
-
 	*flags |= SLAB_KASAN;
 }
 
-- 
2.20.1.415.g653613c723-goog

[PATCH v2 2/3] kasan: make tag based mode work with CONFIG_HARDENED_USERCOPY

[Andrey Konovalov]

With CONFIG_HARDENED_USERCOPY enabled __check_heap_object() compares and
then subtracts a potentially tagged pointer with a non-tagged address of
the page that this pointer belongs to, which leads to unexpected behavior.

Untag the pointer in __check_heap_object() before doing any of these
operations.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/slub.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 36c0befeebd8..1e3d0ec4e200 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3846,6 +3846,8 @@ void __check_heap_object(const void *ptr, unsigned long n, struct page *page,
 	unsigned int offset;
 	size_t object_size;
 
+	ptr = kasan_reset_tag(ptr);
+
 	/* Find object and usable object size. */
 	s = page->slab_cache;
 
-- 
2.20.1.415.g653613c723-goog

[PATCH v2 3/3] kasan: fix krealloc handling for tag-based mode

[Andrey Konovalov]

Right now tag-based KASAN can retag the memory that is reallocated via
krealloc and return a differently tagged pointer even if the same slab
object gets used and no reallocated technically happens.

There are a few issues with this approach. One is that krealloc callers
can't rely on comparing the return value with the passed argument to
check whether reallocation happened. Another is that if a caller knows
that no reallocation happened, that it can access object memory through
the old pointer, which leads to false positives. Look at nf_ct_ext_add()
to see an example.

Fix this by keeping the same tag if the memory don't actually gets
reallocated during krealloc.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/kasan.h | 14 +++++---------
 include/linux/slab.h  |  4 ++--
 mm/kasan/common.c     | 20 ++++++++++++--------
 mm/slab.c             |  8 ++++----
 mm/slab_common.c      |  2 +-
 mm/slub.c             | 10 +++++-----
 6 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b40ea104dd36..7576fff90923 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -57,9 +57,8 @@ void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
 void kasan_kfree_large(void *ptr, unsigned long ip);
 void kasan_poison_kfree(void *ptr, unsigned long ip);
 void * __must_check kasan_kmalloc(struct kmem_cache *s, const void *object,
-					size_t size, gfp_t flags);
-void * __must_check kasan_krealloc(const void *object, size_t new_size,
-					gfp_t flags);
+				size_t size, gfp_t flags, bool krealloc);
+void kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
 
 void * __must_check kasan_slab_alloc(struct kmem_cache *s, void *object,
 					gfp_t flags);
@@ -118,15 +117,12 @@ static inline void *kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags)
 static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
 static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
 static inline void *kasan_kmalloc(struct kmem_cache *s, const void *object,
-				size_t size, gfp_t flags)
-{
-	return (void *)object;
-}
-static inline void *kasan_krealloc(const void *object, size_t new_size,
-				 gfp_t flags)
+				size_t size, gfp_t flags, bool krealloc)
 {
 	return (void *)object;
 }
+static inline void kasan_krealloc(const void *object, size_t new_size,
+				 gfp_t flags) {}
 
 static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
 				   gfp_t flags)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index d87f913ab4e8..1cd168758c05 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -445,7 +445,7 @@ static __always_inline void *kmem_cache_alloc_trace(struct kmem_cache *s,
 {
 	void *ret = kmem_cache_alloc(s, flags);
 
-	ret = kasan_kmalloc(s, ret, size, flags);
+	ret = kasan_kmalloc(s, ret, size, flags, false);
 	return ret;
 }
 
@@ -456,7 +456,7 @@ kmem_cache_alloc_node_trace(struct kmem_cache *s,
 {
 	void *ret = kmem_cache_alloc_node(s, gfpflags, node);
 
-	ret = kasan_kmalloc(s, ret, size, gfpflags);
+	ret = kasan_kmalloc(s, ret, size, gfpflags, false);
 	return ret;
 }
 #endif /* CONFIG_TRACING */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 44390392d4c9..b6633ab86160 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -392,7 +392,7 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
 void * __must_check kasan_slab_alloc(struct kmem_cache *cache, void *object,
 					gfp_t flags)
 {
-	return kasan_kmalloc(cache, object, cache->object_size, flags);
+	return kasan_kmalloc(cache, object, cache->object_size, flags, false);
 }
 
 static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
@@ -451,7 +451,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
 }
 
 void * __must_check kasan_kmalloc(struct kmem_cache *cache, const void *object,
-					size_t size, gfp_t flags)
+				size_t size, gfp_t flags, bool krealloc)
 {
 	unsigned long redzone_start;
 	unsigned long redzone_end;
@@ -468,8 +468,12 @@ void * __must_check kasan_kmalloc(struct kmem_cache *cache, const void *object,
 	redzone_end = round_up((unsigned long)object + cache->object_size,
 				KASAN_SHADOW_SCALE_SIZE);
 
-	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
-		tag = assign_tag(cache, object, false);
+	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) {
+		if (krealloc)
+			tag = get_tag(object);
+		else
+			tag = assign_tag(cache, object, false);
+	}
 
 	/* Tag is ignored in set_tag without CONFIG_KASAN_SW_TAGS */
 	kasan_unpoison_shadow(set_tag(object, tag), size);
@@ -508,19 +512,19 @@ void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
 	return (void *)ptr;
 }
 
-void * __must_check kasan_krealloc(const void *object, size_t size, gfp_t flags)
+void kasan_krealloc(const void *object, size_t size, gfp_t flags)
 {
 	struct page *page;
 
 	if (unlikely(object == ZERO_SIZE_PTR))
-		return (void *)object;
+		return;
 
 	page = virt_to_head_page(object);
 
 	if (unlikely(!PageSlab(page)))
-		return kasan_kmalloc_large(object, size, flags);
+		kasan_kmalloc_large(object, size, flags);
 	else
-		return kasan_kmalloc(page->slab_cache, object, size, flags);
+		kasan_kmalloc(page->slab_cache, object, size, flags, true);
 }
 
 void kasan_poison_kfree(void *ptr, unsigned long ip)
diff --git a/mm/slab.c b/mm/slab.c
index 73fe23e649c9..09b54386cf67 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3604,7 +3604,7 @@ kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)
 
 	ret = slab_alloc(cachep, flags, _RET_IP_);
 
-	ret = kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags, false);
 	trace_kmalloc(_RET_IP_, ret,
 		      size, cachep->size, flags);
 	return ret;
@@ -3647,7 +3647,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,
 
 	ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
 
-	ret = kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags, false);
 	trace_kmalloc_node(_RET_IP_, ret,
 			   size, cachep->size,
 			   flags, nodeid);
@@ -3668,7 +3668,7 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
 	if (unlikely(ZERO_OR_NULL_PTR(cachep)))
 		return cachep;
 	ret = kmem_cache_alloc_node_trace(cachep, flags, node, size);
-	ret = kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags, false);
 
 	return ret;
 }
@@ -3706,7 +3706,7 @@ static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
 		return cachep;
 	ret = slab_alloc(cachep, flags, caller);
 
-	ret = kasan_kmalloc(cachep, ret, size, flags);
+	ret = kasan_kmalloc(cachep, ret, size, flags, false);
 	trace_kmalloc(caller, ret,
 		      size, cachep->size, flags);
 
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 81732d05e74a..b55c58178f83 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1507,7 +1507,7 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 		ks = ksize(p);
 
 	if (ks >= new_size) {
-		p = kasan_krealloc((void *)p, new_size, flags);
+		kasan_krealloc((void *)p, new_size, flags);
 		return (void *)p;
 	}
 
diff --git a/mm/slub.c b/mm/slub.c
index 1e3d0ec4e200..20aa0547acbf 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2763,7 +2763,7 @@ void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
 {
 	void *ret = slab_alloc(s, gfpflags, _RET_IP_);
 	trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags);
-	ret = kasan_kmalloc(s, ret, size, gfpflags);
+	ret = kasan_kmalloc(s, ret, size, gfpflags, false);
 	return ret;
 }
 EXPORT_SYMBOL(kmem_cache_alloc_trace);
@@ -2791,7 +2791,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
 	trace_kmalloc_node(_RET_IP_, ret,
 			   size, s->size, gfpflags, node);
 
-	ret = kasan_kmalloc(s, ret, size, gfpflags);
+	ret = kasan_kmalloc(s, ret, size, gfpflags, false);
 	return ret;
 }
 EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
@@ -3364,7 +3364,7 @@ static void early_kmem_cache_node_alloc(int node)
 	init_tracking(kmem_cache_node, n);
 #endif
 	n = kasan_kmalloc(kmem_cache_node, n, sizeof(struct kmem_cache_node),
-		      GFP_KERNEL);
+		      GFP_KERNEL, false);
 	page->freelist = get_freepointer(kmem_cache_node, n);
 	page->inuse = 1;
 	page->frozen = 0;
@@ -3779,7 +3779,7 @@ void *__kmalloc(size_t size, gfp_t flags)
 
 	trace_kmalloc(_RET_IP_, ret, size, s->size, flags);
 
-	ret = kasan_kmalloc(s, ret, size, flags);
+	ret = kasan_kmalloc(s, ret, size, flags, false);
 
 	return ret;
 }
@@ -3823,7 +3823,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
 
 	trace_kmalloc_node(_RET_IP_, ret, size, s->size, flags, node);
 
-	ret = kasan_kmalloc(s, ret, size, flags);
+	ret = kasan_kmalloc(s, ret, size, flags, false);
 
 	return ret;
 }
-- 
2.20.1.415.g653613c723-goog

Re: [PATCH v2 1/3] kasan, arm64: use ARCH_SLAB_MINALIGN instead of manual aligning

[Andrew Morton]

On Wed,  2 Jan 2019 18:36:06 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:

> Instead of changing cache->align to be aligned to KASAN_SHADOW_SCALE_SIZE
> in kasan_cache_create() we can reuse the ARCH_SLAB_MINALIGN macro.
> 
> ...
>
> --- a/arch/arm64/include/asm/kasan.h
> +++ b/arch/arm64/include/asm/kasan.h
> @@ -36,6 +36,10 @@
>  #define KASAN_SHADOW_OFFSET     (KASAN_SHADOW_END - (1ULL << \
>  					(64 - KASAN_SHADOW_SCALE_SHIFT)))
>  
> +#ifdef CONFIG_KASAN_SW_TAGS
> +#define ARCH_SLAB_MINALIGN	(1ULL << KASAN_SHADOW_SCALE_SHIFT)
> +#endif
> +
>  void kasan_init(void);
>  void kasan_copy_shadow(pgd_t *pgdir);
>  asmlinkage void kasan_early_init(void);
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 11b45f7ae405..d87f913ab4e8 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -16,6 +16,7 @@
>  #include <linux/overflow.h>
>  #include <linux/types.h>
>  #include <linux/workqueue.h>
> +#include <linux/kasan.h>
>  

This still seems unadvisable.  Like other architectures, arm defines
ARCH_SLAB_MINALIGN in arch/arm/include/asm/cache.h. 
arch/arm/include/asm64/cache.h doesn't define ARCH_SLAB_MINALIGN
afaict.

If arch/arm/include/asm64/cache.h later gets a definition of
ARCH_SLAB_MINALIGN then we again face the risk that different .c files
will see different values of ARCH_SLAB_MINALIGN depending on which
headers they include.

So what to say about this?  The architecture's ARCH_SLAB_MINALIGN
should be defined in the architecture's cache.h, end of story.  Not in
slab.h, not in kasan.h.

Re: [PATCH v2 3/3] kasan: fix krealloc handling for tag-based mode

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1832 bytes --]

Hi Andrey,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on next-20190102]
[cannot apply to v4.20]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Andrey-Konovalov/kasan-tag-based-mode-fixes/20190103-050707
config: x86_64-randconfig-x016-201900 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   mm/kasan/common.c: In function 'kasan_krealloc':
>> mm/kasan/common.c:525:3: warning: ignoring return value of 'kasan_kmalloc_large', declared with attribute warn_unused_result [-Wunused-result]
      kasan_kmalloc_large(object, size, flags);
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> mm/kasan/common.c:527:3: warning: ignoring return value of 'kasan_kmalloc', declared with attribute warn_unused_result [-Wunused-result]
      kasan_kmalloc(page->slab_cache, object, size, flags, true);
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

vim +/kasan_kmalloc_large +525 mm/kasan/common.c

   514	
   515	void kasan_krealloc(const void *object, size_t size, gfp_t flags)
   516	{
   517		struct page *page;
   518	
   519		if (unlikely(object == ZERO_SIZE_PTR))
   520			return;
   521	
   522		page = virt_to_head_page(object);
   523	
   524		if (unlikely(!PageSlab(page)))
 > 525			kasan_kmalloc_large(object, size, flags);
   526		else
 > 527			kasan_kmalloc(page->slab_cache, object, size, flags, true);
   528	}
   529	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 29147 bytes --]

Re: [PATCH v2 1/3] kasan, arm64: use ARCH_SLAB_MINALIGN instead of manual aligning

[Will Deacon]

On Wed, Jan 02, 2019 at 12:14:36PM -0800, Andrew Morton wrote:
> On Wed,  2 Jan 2019 18:36:06 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:
> 
> > Instead of changing cache->align to be aligned to KASAN_SHADOW_SCALE_SIZE
> > in kasan_cache_create() we can reuse the ARCH_SLAB_MINALIGN macro.
> > 
> > ...
> >
> > --- a/arch/arm64/include/asm/kasan.h
> > +++ b/arch/arm64/include/asm/kasan.h
> > @@ -36,6 +36,10 @@
> >  #define KASAN_SHADOW_OFFSET     (KASAN_SHADOW_END - (1ULL << \
> >  					(64 - KASAN_SHADOW_SCALE_SHIFT)))
> >  
> > +#ifdef CONFIG_KASAN_SW_TAGS
> > +#define ARCH_SLAB_MINALIGN	(1ULL << KASAN_SHADOW_SCALE_SHIFT)
> > +#endif
> > +
> >  void kasan_init(void);
> >  void kasan_copy_shadow(pgd_t *pgdir);
> >  asmlinkage void kasan_early_init(void);
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 11b45f7ae405..d87f913ab4e8 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -16,6 +16,7 @@
> >  #include <linux/overflow.h>
> >  #include <linux/types.h>
> >  #include <linux/workqueue.h>
> > +#include <linux/kasan.h>
> >  
> 
> This still seems unadvisable.  Like other architectures, arm defines
> ARCH_SLAB_MINALIGN in arch/arm/include/asm/cache.h. 
> arch/arm/include/asm64/cache.h doesn't define ARCH_SLAB_MINALIGN
> afaict.
> 
> If arch/arm/include/asm64/cache.h later gets a definition of
> ARCH_SLAB_MINALIGN then we again face the risk that different .c files
> will see different values of ARCH_SLAB_MINALIGN depending on which
> headers they include.
> 
> So what to say about this?  The architecture's ARCH_SLAB_MINALIGN
> should be defined in the architecture's cache.h, end of story.  Not in
> slab.h, not in kasan.h.

Agreed. Also, as far as I can tell, this patch isn't actually a fix (unlike
the other two in this series) so it should be harmless to drop it for now.

Will

Re: [PATCH v2 1/3] kasan, arm64: use ARCH_SLAB_MINALIGN instead of manual aligning

[Andrey Konovalov]

On Wed, Jan 2, 2019 at 9:14 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed,  2 Jan 2019 18:36:06 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:
>
> > Instead of changing cache->align to be aligned to KASAN_SHADOW_SCALE_SIZE
> > in kasan_cache_create() we can reuse the ARCH_SLAB_MINALIGN macro.
> >
> > ...
> >
> > --- a/arch/arm64/include/asm/kasan.h
> > +++ b/arch/arm64/include/asm/kasan.h
> > @@ -36,6 +36,10 @@
> >  #define KASAN_SHADOW_OFFSET     (KASAN_SHADOW_END - (1ULL << \
> >                                       (64 - KASAN_SHADOW_SCALE_SHIFT)))
> >
> > +#ifdef CONFIG_KASAN_SW_TAGS
> > +#define ARCH_SLAB_MINALIGN   (1ULL << KASAN_SHADOW_SCALE_SHIFT)
> > +#endif
> > +
> >  void kasan_init(void);
> >  void kasan_copy_shadow(pgd_t *pgdir);
> >  asmlinkage void kasan_early_init(void);
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 11b45f7ae405..d87f913ab4e8 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -16,6 +16,7 @@
> >  #include <linux/overflow.h>
> >  #include <linux/types.h>
> >  #include <linux/workqueue.h>
> > +#include <linux/kasan.h>
> >
>
> This still seems unadvisable.  Like other architectures, arm defines
> ARCH_SLAB_MINALIGN in arch/arm/include/asm/cache.h.
> arch/arm/include/asm64/cache.h doesn't define ARCH_SLAB_MINALIGN
> afaict.
>
> If arch/arm/include/asm64/cache.h later gets a definition of
> ARCH_SLAB_MINALIGN then we again face the risk that different .c files
> will see different values of ARCH_SLAB_MINALIGN depending on which
> headers they include.
>
> So what to say about this?  The architecture's ARCH_SLAB_MINALIGN
> should be defined in the architecture's cache.h, end of story.  Not in
> slab.h, not in kasan.h.

Done in v3, thanks!

>
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