linux-kernel - Re: [PATCH v2] kasan, mm: fix crash with HW_TAGS and DEBUG

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Date:   Fri, 5 Mar 2021 17:27:07 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Marco Elver <elver@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] kasan, mm: fix crash with HW_TAGS and
 DEBUG_PAGEALLOC

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

> On Sat, Mar 6, 2021 at 12:50 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Sat,  6 Mar 2021 00:36:33 +0100 Andrey Konovalov <andreyknvl@...gle.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.