[PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[yee.lee]

From: Yee Lee <yee.lee@mediatek.com>

Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite
the redzone of object with unaligned size.

An additional memzero_explicit() path is added to replacing init by
hwtag instruction for those unaligned size at SLUB debug mode.

Signed-off-by: Yee Lee <yee.lee@mediatek.com>
---
 mm/kasan/kasan.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 8f450bc28045..d1054f35838f 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -387,6 +387,12 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
 
 	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
 		return;
+#if IS_ENABLED(CONFIG_SLUB_DEBUG)
+	if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
+		init = false;
+		memzero_explicit((void *)addr, size);
+	}
+#endif
 	size = round_up(size, KASAN_GRANULE_SIZE);
 
 	hw_set_mem_tag_range((void *)addr, size, tag, init);
-- 
2.18.0

Re: [PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[Andrey Konovalov]

On Thu, Jun 24, 2021 at 2:26 PM <yee.lee@mediatek.com> wrote:
>
> From: Yee Lee <yee.lee@mediatek.com>
>
> Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite
> the redzone of object with unaligned size.
>
> An additional memzero_explicit() path is added to replacing init by
> hwtag instruction for those unaligned size at SLUB debug mode.
>
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> ---
>  mm/kasan/kasan.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8f450bc28045..d1054f35838f 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -387,6 +387,12 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
>
>         if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
>                 return;
> +#if IS_ENABLED(CONFIG_SLUB_DEBUG)

Is this an issue only with SLUB? SLAB also uses redzones.

> +       if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {

This needs a comment along the lines of:

/* Explicitly initialize the memory with the precise object size to
avoid overwriting the SLAB redzone. This disables initialization in
the arch code and may thus lead to performance penalty. The penalty is
accepted since SLAB redzones aren't enabled in production builds. */

> +               init = false;
> +               memzero_explicit((void *)addr, size);
> +       }
> +#endif
>         size = round_up(size, KASAN_GRANULE_SIZE);
>
>         hw_set_mem_tag_range((void *)addr, size, tag, init);
> --
> 2.18.0
>

Re: [PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[Yee Lee]

On Fri, 2021-06-25 at 17:03 +0300, Andrey Konovalov wrote:
> On Thu, Jun 24, 2021 at 2:26 PM <yee.lee@mediatek.com> wrote:
> > 
> > From: Yee Lee <yee.lee@mediatek.com>
> > 
> > Issue: when SLUB debug is on, hwtag kasan_unpoison() would
> > overwrite
> > the redzone of object with unaligned size.
> > 
> > An additional memzero_explicit() path is added to replacing init by
> > hwtag instruction for those unaligned size at SLUB debug mode.
> > 
> > Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> > ---
> >  mm/kasan/kasan.h | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index 8f450bc28045..d1054f35838f 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -387,6 +387,12 @@ static inline void kasan_unpoison(const void
> > *addr, size_t size, bool init)
> > 
> >         if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
> >                 return;
> > +#if IS_ENABLED(CONFIG_SLUB_DEBUG)
> 
> Is this an issue only with SLUB? SLAB also uses redzones.
As I known, hw-tag kasan only works with SLUB.

> 
> > +       if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
> 
> This needs a comment along the lines of:
> 
> /* Explicitly initialize the memory with the precise object size to
> avoid overwriting the SLAB redzone. This disables initialization in
> the arch code and may thus lead to performance penalty. The penalty
> is
> accepted since SLAB redzones aren't enabled in production builds. */
Sure, will work on this.
> 
> > +               init = false;
> > +               memzero_explicit((void *)addr, size);
> > +       }
> > +#endif
> >         size = round_up(size, KASAN_GRANULE_SIZE);
> > 
> >         hw_set_mem_tag_range((void *)addr, size, tag, init);
> > --
> > 2.18.0
> > 

Re: [PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[Marco Elver]

On Thu, 24 Jun 2021 at 13:27, <yee.lee@mediatek.com> wrote:
>
> From: Yee Lee <yee.lee@mediatek.com>
>
> Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite
> the redzone of object with unaligned size.
>
> An additional memzero_explicit() path is added to replacing init by
> hwtag instruction for those unaligned size at SLUB debug mode.
>
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> ---
>  mm/kasan/kasan.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8f450bc28045..d1054f35838f 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -387,6 +387,12 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
>
>         if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
>                 return;
> +#if IS_ENABLED(CONFIG_SLUB_DEBUG)

Avoid the #if. I think none of the stuff referenced here is only
available if CONFIG_SLUB_DEBUG. In that case, please just write:

if (IS_ENABLED(CONFIG_SLUB_DEBUG) && init && .........) {

The compiler will correctly optimize out the branch if the config
option is not enabled. But the benefit is we compile-test this code
with all configs.

> +       if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
> +               init = false;
> +               memzero_explicit((void *)addr, size);
> +       }
> +#endif

Thanks,
-- Marco

[PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[yee.lee]

From: Yee Lee <yee.lee@mediatek.com>

Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite the redzone with unaligned object size.

An additional memzero_explicit() path is added to replacing hwtag initialization
at SLUB deubg mode.

Signed-off-by: Yee Lee <yee.lee@mediatek.com>
Suggested-by: Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/kasan/kasan.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index d8faa64614b7..e984a9ac814d 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -387,10 +387,12 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
 
 	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
 		return;
+	#if IS_ENABLED(CONFIG_SLUB_DEBUG)
 	if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
 		init = false;
-		memset((void *)addr, 0, size);
+		memzero_explicit((void *)addr, size);
 	}
+	#endif
 	size = round_up(size, KASAN_GRANULE_SIZE);
 	hw_set_mem_tag_range((void *)addr, size, tag, init);
 }
-- 
2.18.0

Re: [PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

[Yee Lee]

Sorry not a completed patch.
Please skip this mail.

BR,
Yee

On Wed, 2021-06-23 at 21:35 +0800, yee.lee@mediatek.com wrote:
> From: Yee Lee <yee.lee@mediatek.com>
> 
> Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite
> the redzone with unaligned object size.
> 
> An additional memzero_explicit() path is added to replacing hwtag
> initialization
> at SLUB deubg mode.
> 
> Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> Suggested-by: Marco Elver <elver@google.com>
> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Andrey Konovalov <andreyknvl@gmail.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  mm/kasan/kasan.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index d8faa64614b7..e984a9ac814d 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -387,10 +387,12 @@ static inline void kasan_unpoison(const void
> *addr, size_t size, bool init)
>  
>  	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
>  		return;
> +	#if IS_ENABLED(CONFIG_SLUB_DEBUG)
>  	if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
>  		init = false;
> -		memset((void *)addr, 0, size);
> +		memzero_explicit((void *)addr, size);
>  	}
> +	#endif
>  	size = round_up(size, KASAN_GRANULE_SIZE);
>  	hw_set_mem_tag_range((void *)addr, size, tag, init);
>  }