diff mbox series

kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC

Message ID 1aa83e48627978de8068d5e3314185f3a0d7a849.1614302398.git.andreyknvl@google.com (mailing list archive)
State New
Headers show
Series kasan, mm: fix crash with HW_TAGS and DEBUG_PAGEALLOC | expand

Commit Message

Andrey Konovalov Feb. 26, 2021, 1:25 a.m. UTC
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().

Besides fixing the crash, this also makes the annotation order consistent
with debug_pagealloc_map_pages() preceding kasan_alloc_pages().

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/page_alloc.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Comments

Andrew Morton March 3, 2021, 11:23 p.m. UTC | #1
On Fri, 26 Feb 2021 02:25:37 +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().
> 
> Besides fixing the crash, this also makes the annotation order consistent
> with debug_pagealloc_map_pages() preceding kasan_alloc_pages().
> 

This bug exists in 5.12, does it not?

If so, is cc:stable appropriate and if so, do we have a suitable Fixes:
commit?

Thanks.
Andrey Konovalov March 5, 2021, 3:43 p.m. UTC | #2
On Thu, Mar 4, 2021 at 12:23 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Fri, 26 Feb 2021 02:25:37 +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().
> >
> > Besides fixing the crash, this also makes the annotation order consistent
> > with debug_pagealloc_map_pages() preceding kasan_alloc_pages().
> >
>
> This bug exists in 5.12, does it not?
>
> If so, is cc:stable appropriate and if so, do we have a suitable Fixes:
> commit?

Sure:

Fixes: 94ab5b61ee16  ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
Cc: <stable@vger.kernel.org>
Andrey Konovalov March 5, 2021, 5:04 p.m. UTC | #3
On Fri, Feb 26, 2021 at 2:25 AM 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().
>
> Besides fixing the crash, this also makes the annotation order consistent
> with debug_pagealloc_map_pages() preceding kasan_alloc_pages().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  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 c89e7b107514..54bc237fd319 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1311,10 +1311,14 @@ static __always_inline bool free_pages_prepare(struct page *page,
>          */
>         arch_free_page(page, order);
>
> -       debug_pagealloc_unmap_pages(page, 1 << order);
> -
> +       /*
> +        * With hardware tag-based KASAN, memory tags must be set
> +        * before unmapping the page with debug_pagealloc.
> +        */
>         kasan_free_nondeferred_pages(page, order, fpi_flags);

Looking at this again, I think we need to move kasan_() callback above
arch_free_page(), as that can also make the page unavailable. I'll
send v2.
diff mbox series

Patch

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c89e7b107514..54bc237fd319 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1311,10 +1311,14 @@  static __always_inline bool free_pages_prepare(struct page *page,
 	 */
 	arch_free_page(page, order);
 
-	debug_pagealloc_unmap_pages(page, 1 << order);
-
+	/*
+	 * With hardware tag-based KASAN, memory tags must be set
+	 * before unmapping the page with debug_pagealloc.
+	 */
 	kasan_free_nondeferred_pages(page, order, fpi_flags);
 
+	debug_pagealloc_unmap_pages(page, 1 << order);
+
 	return true;
 }