[PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[Andrey Konovalov]

Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
after debug_pagealloc_unmap_pages(). This causes a crash when
debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
unmapped page.

This patch puts kasan_free_nondeferred_pages() before
debug_pagealloc_unmap_pages() and arch_free_page(), which can also make
the page unavailable.

Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v1->v2:
- Move kasan_free_nondeferred_pages() before arch_free_page().

---
 mm/page_alloc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 969e7012fce0..0efb07b5907c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1304,6 +1304,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
 
 	kernel_poison_pages(page, 1 << order);
 
+	/*
+	 * With hardware tag-based KASAN, memory tags must be set before the
+	 * page becomes unavailable via debug_pagealloc or arch_free_page.
+	 */
+	kasan_free_nondeferred_pages(page, order, fpi_flags);
+
 	/*
 	 * arch_free_page() can make the page's contents inaccessible.  s390
 	 * does this.  So nothing which can access the page's contents should
@@ -1313,8 +1319,6 @@ static __always_inline bool free_pages_prepare(struct page *page,
 
 	debug_pagealloc_unmap_pages(page, 1 << order);
 
-	kasan_free_nondeferred_pages(page, order, fpi_flags);
-
 	return true;
 }
 
-- 
2.30.1.766.gb4fecdf3b7-goog

Re: [PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[Andrew Morton]

On Sat,  6 Mar 2021 00:36:33 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:

> Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
> after debug_pagealloc_unmap_pages(). This causes a crash when
> debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
> unmapped page.
> 
> This patch puts kasan_free_nondeferred_pages() before
> debug_pagealloc_unmap_pages() and arch_free_page(), which can also make
> the page unavailable.
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1304,6 +1304,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
>  
>  	kernel_poison_pages(page, 1 << order);
>  
> +	/*
> +	 * With hardware tag-based KASAN, memory tags must be set before the
> +	 * page becomes unavailable via debug_pagealloc or arch_free_page.
> +	 */
> +	kasan_free_nondeferred_pages(page, order, fpi_flags);
> +
>  	/*
>  	 * arch_free_page() can make the page's contents inaccessible.  s390
>  	 * does this.  So nothing which can access the page's contents should
> @@ -1313,8 +1319,6 @@ static __always_inline bool free_pages_prepare(struct page *page,
>  
>  	debug_pagealloc_unmap_pages(page, 1 << order);
>  
> -	kasan_free_nondeferred_pages(page, order, fpi_flags);
> -
>  	return true;
>  }

kasan_free_nondeferred_pages() has only two args in current mainline.

I fixed that in the obvious manner...

Re: [PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[Andrey Konovalov]

On Sat, Mar 6, 2021 at 12:50 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Sat,  6 Mar 2021 00:36:33 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:
>
> > Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
> > after debug_pagealloc_unmap_pages(). This causes a crash when
> > debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
> > unmapped page.
> >
> > This patch puts kasan_free_nondeferred_pages() before
> > debug_pagealloc_unmap_pages() and arch_free_page(), which can also make
> > the page unavailable.
> >
> > ...
> >
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1304,6 +1304,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
> >
> >       kernel_poison_pages(page, 1 << order);
> >
> > +     /*
> > +      * With hardware tag-based KASAN, memory tags must be set before the
> > +      * page becomes unavailable via debug_pagealloc or arch_free_page.
> > +      */
> > +     kasan_free_nondeferred_pages(page, order, fpi_flags);
> > +
> >       /*
> >        * arch_free_page() can make the page's contents inaccessible.  s390
> >        * does this.  So nothing which can access the page's contents should
> > @@ -1313,8 +1319,6 @@ static __always_inline bool free_pages_prepare(struct page *page,
> >
> >       debug_pagealloc_unmap_pages(page, 1 << order);
> >
> > -     kasan_free_nondeferred_pages(page, order, fpi_flags);
> > -
> >       return true;
> >  }
>
> kasan_free_nondeferred_pages() has only two args in current mainline.

Ah, yes, forgot to mention: this goes on top of:

kasan: initialize shadow to TAG_INVALID for SW_TAGS
mm, kasan: don't poison boot memory with tag-based modes

>
> I fixed that in the obvious manner...

Thanks!

If you changed this patch, you'll also need to change the other one though.

Re: [PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[Andrey Konovalov]

On Sat, Mar 6, 2021 at 12:54 AM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> On Sat, Mar 6, 2021 at 12:50 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Sat,  6 Mar 2021 00:36:33 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:
> >
> > > Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
> > > after debug_pagealloc_unmap_pages(). This causes a crash when
> > > debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
> > > unmapped page.
> > >
> > > This patch puts kasan_free_nondeferred_pages() before
> > > debug_pagealloc_unmap_pages() and arch_free_page(), which can also make
> > > the page unavailable.
> > >
> > > ...
> > >
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1304,6 +1304,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
> > >
> > >       kernel_poison_pages(page, 1 << order);
> > >
> > > +     /*
> > > +      * With hardware tag-based KASAN, memory tags must be set before the
> > > +      * page becomes unavailable via debug_pagealloc or arch_free_page.
> > > +      */
> > > +     kasan_free_nondeferred_pages(page, order, fpi_flags);
> > > +
> > >       /*
> > >        * arch_free_page() can make the page's contents inaccessible.  s390
> > >        * does this.  So nothing which can access the page's contents should
> > > @@ -1313,8 +1319,6 @@ static __always_inline bool free_pages_prepare(struct page *page,
> > >
> > >       debug_pagealloc_unmap_pages(page, 1 << order);
> > >
> > > -     kasan_free_nondeferred_pages(page, order, fpi_flags);
> > > -
> > >       return true;
> > >  }
> >
> > kasan_free_nondeferred_pages() has only two args in current mainline.
>
> Ah, yes, forgot to mention: this goes on top of:
>
> kasan: initialize shadow to TAG_INVALID for SW_TAGS
> mm, kasan: don't poison boot memory with tag-based modes
>
> >
> > I fixed that in the obvious manner...
>
> Thanks!
>
> If you changed this patch, you'll also need to change the other one though.

Nevermind, just realized that this should be a backportable fix :)

Re: [PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

[Andrew Morton]

On Sat, 6 Mar 2021 00:54:32 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:

> On Sat, Mar 6, 2021 at 12:50 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Sat,  6 Mar 2021 00:36:33 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:
> >
> > > Currently, kasan_free_nondeferred_pages()->kasan_free_pages() is called
> > > after debug_pagealloc_unmap_pages(). This causes a crash when
> > > debug_pagealloc is enabled, as HW_TAGS KASAN can't set tags on an
> > > unmapped page.
> > >
> > > This patch puts kasan_free_nondeferred_pages() before
> > > debug_pagealloc_unmap_pages() and arch_free_page(), which can also make
> > > the page unavailable.
> > >
> > > ...
> > >
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1304,6 +1304,12 @@ static __always_inline bool free_pages_prepare(struct page *page,
> > >
> > >       kernel_poison_pages(page, 1 << order);
> > >
> > > +     /*
> > > +      * With hardware tag-based KASAN, memory tags must be set before the
> > > +      * page becomes unavailable via debug_pagealloc or arch_free_page.
> > > +      */
> > > +     kasan_free_nondeferred_pages(page, order, fpi_flags);
> > > +
> > >       /*
> > >        * arch_free_page() can make the page's contents inaccessible.  s390
> > >        * does this.  So nothing which can access the page's contents should
> > > @@ -1313,8 +1319,6 @@ static __always_inline bool free_pages_prepare(struct page *page,
> > >
> > >       debug_pagealloc_unmap_pages(page, 1 << order);
> > >
> > > -     kasan_free_nondeferred_pages(page, order, fpi_flags);
> > > -
> > >       return true;
> > >  }
> >
> > kasan_free_nondeferred_pages() has only two args in current mainline.
> 
> Ah, yes, forgot to mention: this goes on top of:
> 
> kasan: initialize shadow to TAG_INVALID for SW_TAGS
> mm, kasan: don't poison boot memory with tag-based modes

This patch (kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC) is
cc:stable, so it should come head of the other two lower priority
patches.

> >
> > I fixed that in the obvious manner...
> 
> Thanks!
> 
> If you changed this patch, you'll also need to change the other one though.


Yup.