diff mbox series

[mm,v3,18/19] kasan, mm: allow cache merging with no metadata

Message ID 6f0a1e72783ddac000ac08e7315b1d7c0ca4ec51.1605305978.git.andreyknvl@google.com (mailing list archive)
State New
Headers show
Series kasan: boot parameters for hardware tag-based mode | expand

Commit Message

Andrey Konovalov Nov. 13, 2020, 10:20 p.m. UTC
The reason cache merging is disabled with KASAN is because KASAN puts its
metadata right after the allocated object. When the merged caches have
slightly different sizes, the metadata ends up in different places, which
KASAN doesn't support.

It might be possible to adjust the metadata allocation algorithm and make
it friendly to the cache merging code. Instead this change takes a simpler
approach and allows merging caches when no metadata is present. Which is
the case for hardware tag-based KASAN with kasan.mode=prod.

Co-developed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Signed-off-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://linux-review.googlesource.com/id/Ia114847dfb2244f297d2cb82d592bf6a07455dba
---
 include/linux/kasan.h | 21 +++++++++++++++++++--
 mm/kasan/common.c     | 11 +++++++++++
 mm/slab_common.c      |  3 ++-
 3 files changed, 32 insertions(+), 3 deletions(-)

Comments

Marco Elver Nov. 16, 2020, 3:45 p.m. UTC | #1
On Fri, Nov 13, 2020 at 11:20PM +0100, Andrey Konovalov wrote:
> The reason cache merging is disabled with KASAN is because KASAN puts its
> metadata right after the allocated object. When the merged caches have
> slightly different sizes, the metadata ends up in different places, which
> KASAN doesn't support.
> 
> It might be possible to adjust the metadata allocation algorithm and make
> it friendly to the cache merging code. Instead this change takes a simpler
> approach and allows merging caches when no metadata is present. Which is
> the case for hardware tag-based KASAN with kasan.mode=prod.
> 
> Co-developed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> Signed-off-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Link: https://linux-review.googlesource.com/id/Ia114847dfb2244f297d2cb82d592bf6a07455dba

Reviewed-by: Marco Elver <elver@google.com>

> ---
>  include/linux/kasan.h | 21 +++++++++++++++++++--
>  mm/kasan/common.c     | 11 +++++++++++
>  mm/slab_common.c      |  3 ++-
>  3 files changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 16cf53eac29b..173a8e81d001 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -81,17 +81,30 @@ struct kasan_cache {
>  };
>  
>  #ifdef CONFIG_KASAN_HW_TAGS
> +
>  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
> +
>  static __always_inline bool kasan_enabled(void)
>  {
>  	return static_branch_likely(&kasan_flag_enabled);
>  }
> -#else
> +
> +#else /* CONFIG_KASAN_HW_TAGS */
> +
>  static inline bool kasan_enabled(void)
>  {
>  	return true;
>  }
> -#endif
> +
> +#endif /* CONFIG_KASAN_HW_TAGS */
> +
> +slab_flags_t __kasan_never_merge(void);
> +static __always_inline slab_flags_t kasan_never_merge(void)
> +{
> +	if (kasan_enabled())
> +		return __kasan_never_merge();
> +	return 0;
> +}
>  
>  void __kasan_unpoison_range(const void *addr, size_t size);
>  static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
> @@ -238,6 +251,10 @@ static inline bool kasan_enabled(void)
>  {
>  	return false;
>  }
> +static inline slab_flags_t kasan_never_merge(void)
> +{
> +	return 0;
> +}
>  static inline void kasan_unpoison_range(const void *address, size_t size) {}
>  static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
>  static inline void kasan_free_pages(struct page *page, unsigned int order) {}
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index cf874243efab..a5a4dcb1254d 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -87,6 +87,17 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
>  }
>  #endif /* CONFIG_KASAN_STACK */
>  
> +/*
> + * Only allow cache merging when stack collection is disabled and no metadata
> + * is present.
> + */
> +slab_flags_t __kasan_never_merge(void)
> +{
> +	if (kasan_stack_collection_enabled())
> +		return SLAB_KASAN;
> +	return 0;
> +}
> +
>  void __kasan_alloc_pages(struct page *page, unsigned int order)
>  {
>  	u8 tag;
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 0b5ae1819a8b..075b23ce94ec 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -19,6 +19,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/proc_fs.h>
>  #include <linux/debugfs.h>
> +#include <linux/kasan.h>
>  #include <asm/cacheflush.h>
>  #include <asm/tlbflush.h>
>  #include <asm/page.h>
> @@ -54,7 +55,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
>   */
>  #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
>  		SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
> -		SLAB_FAILSLAB | SLAB_KASAN)
> +		SLAB_FAILSLAB | kasan_never_merge())
>  
>  #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
>  			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)
> -- 
> 2.29.2.299.gdc1121823c-goog
>
Dmitry Vyukov Nov. 17, 2020, 1:25 p.m. UTC | #2
On Fri, Nov 13, 2020 at 11:20 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> The reason cache merging is disabled with KASAN is because KASAN puts its
> metadata right after the allocated object. When the merged caches have
> slightly different sizes, the metadata ends up in different places, which
> KASAN doesn't support.
>
> It might be possible to adjust the metadata allocation algorithm and make
> it friendly to the cache merging code. Instead this change takes a simpler
> approach and allows merging caches when no metadata is present. Which is
> the case for hardware tag-based KASAN with kasan.mode=prod.
>
> Co-developed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> Signed-off-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> Link: https://linux-review.googlesource.com/id/Ia114847dfb2244f297d2cb82d592bf6a07455dba

Somehow gerrit contains an old version... so I was going to
independently propose what Marco already proposed as simplification...
until I looked at the patch in the email :)

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

> ---
>  include/linux/kasan.h | 21 +++++++++++++++++++--
>  mm/kasan/common.c     | 11 +++++++++++
>  mm/slab_common.c      |  3 ++-
>  3 files changed, 32 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 16cf53eac29b..173a8e81d001 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -81,17 +81,30 @@ struct kasan_cache {
>  };
>
>  #ifdef CONFIG_KASAN_HW_TAGS
> +
>  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
> +
>  static __always_inline bool kasan_enabled(void)
>  {
>         return static_branch_likely(&kasan_flag_enabled);
>  }
> -#else
> +
> +#else /* CONFIG_KASAN_HW_TAGS */
> +
>  static inline bool kasan_enabled(void)
>  {
>         return true;
>  }
> -#endif
> +
> +#endif /* CONFIG_KASAN_HW_TAGS */
> +
> +slab_flags_t __kasan_never_merge(void);
> +static __always_inline slab_flags_t kasan_never_merge(void)
> +{
> +       if (kasan_enabled())
> +               return __kasan_never_merge();
> +       return 0;
> +}
>
>  void __kasan_unpoison_range(const void *addr, size_t size);
>  static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
> @@ -238,6 +251,10 @@ static inline bool kasan_enabled(void)
>  {
>         return false;
>  }
> +static inline slab_flags_t kasan_never_merge(void)
> +{
> +       return 0;
> +}
>  static inline void kasan_unpoison_range(const void *address, size_t size) {}
>  static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
>  static inline void kasan_free_pages(struct page *page, unsigned int order) {}
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index cf874243efab..a5a4dcb1254d 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -87,6 +87,17 @@ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
>  }
>  #endif /* CONFIG_KASAN_STACK */
>
> +/*
> + * Only allow cache merging when stack collection is disabled and no metadata
> + * is present.
> + */
> +slab_flags_t __kasan_never_merge(void)
> +{
> +       if (kasan_stack_collection_enabled())
> +               return SLAB_KASAN;
> +       return 0;
> +}
> +
>  void __kasan_alloc_pages(struct page *page, unsigned int order)
>  {
>         u8 tag;
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 0b5ae1819a8b..075b23ce94ec 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -19,6 +19,7 @@
>  #include <linux/seq_file.h>
>  #include <linux/proc_fs.h>
>  #include <linux/debugfs.h>
> +#include <linux/kasan.h>
>  #include <asm/cacheflush.h>
>  #include <asm/tlbflush.h>
>  #include <asm/page.h>
> @@ -54,7 +55,7 @@ static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
>   */
>  #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
>                 SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
> -               SLAB_FAILSLAB | SLAB_KASAN)
> +               SLAB_FAILSLAB | kasan_never_merge())
>
>  #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
>                          SLAB_CACHE_DMA32 | SLAB_ACCOUNT)
> --
> 2.29.2.299.gdc1121823c-goog
>
Andrey Konovalov Nov. 23, 2020, 1:52 p.m. UTC | #3
On Tue, Nov 17, 2020 at 2:25 PM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Fri, Nov 13, 2020 at 11:20 PM Andrey Konovalov <andreyknvl@google.com> wrote:
> >
> > The reason cache merging is disabled with KASAN is because KASAN puts its
> > metadata right after the allocated object. When the merged caches have
> > slightly different sizes, the metadata ends up in different places, which
> > KASAN doesn't support.
> >
> > It might be possible to adjust the metadata allocation algorithm and make
> > it friendly to the cache merging code. Instead this change takes a simpler
> > approach and allows merging caches when no metadata is present. Which is
> > the case for hardware tag-based KASAN with kasan.mode=prod.
> >
> > Co-developed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> > Signed-off-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> > Link: https://linux-review.googlesource.com/id/Ia114847dfb2244f297d2cb82d592bf6a07455dba
>
> Somehow gerrit contains an old version... so I was going to
> independently propose what Marco already proposed as simplification...
> until I looked at the patch in the email :)

Ah, this is because I couldn't push next/mm-based changes into Gerrit
without manually adding tags to all of the yet-out-of-tree patches. So
the Gerrit doesn't have the last version of the patchset.

> Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

Thanks!
diff mbox series

Patch

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 16cf53eac29b..173a8e81d001 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -81,17 +81,30 @@  struct kasan_cache {
 };
 
 #ifdef CONFIG_KASAN_HW_TAGS
+
 DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
+
 static __always_inline bool kasan_enabled(void)
 {
 	return static_branch_likely(&kasan_flag_enabled);
 }
-#else
+
+#else /* CONFIG_KASAN_HW_TAGS */
+
 static inline bool kasan_enabled(void)
 {
 	return true;
 }
-#endif
+
+#endif /* CONFIG_KASAN_HW_TAGS */
+
+slab_flags_t __kasan_never_merge(void);
+static __always_inline slab_flags_t kasan_never_merge(void)
+{
+	if (kasan_enabled())
+		return __kasan_never_merge();
+	return 0;
+}
 
 void __kasan_unpoison_range(const void *addr, size_t size);
 static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
@@ -238,6 +251,10 @@  static inline bool kasan_enabled(void)
 {
 	return false;
 }
+static inline slab_flags_t kasan_never_merge(void)
+{
+	return 0;
+}
 static inline void kasan_unpoison_range(const void *address, size_t size) {}
 static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
 static inline void kasan_free_pages(struct page *page, unsigned int order) {}
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index cf874243efab..a5a4dcb1254d 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -87,6 +87,17 @@  asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
 }
 #endif /* CONFIG_KASAN_STACK */
 
+/*
+ * Only allow cache merging when stack collection is disabled and no metadata
+ * is present.
+ */
+slab_flags_t __kasan_never_merge(void)
+{
+	if (kasan_stack_collection_enabled())
+		return SLAB_KASAN;
+	return 0;
+}
+
 void __kasan_alloc_pages(struct page *page, unsigned int order)
 {
 	u8 tag;
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 0b5ae1819a8b..075b23ce94ec 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -19,6 +19,7 @@ 
 #include <linux/seq_file.h>
 #include <linux/proc_fs.h>
 #include <linux/debugfs.h>
+#include <linux/kasan.h>
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
 #include <asm/page.h>
@@ -54,7 +55,7 @@  static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
  */
 #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
 		SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
-		SLAB_FAILSLAB | SLAB_KASAN)
+		SLAB_FAILSLAB | kasan_never_merge())
 
 #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
 			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)