From: Marco Elver <elver@google.com>
To: Jann Horn <jannh@google.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Alexander Potapenko" <glider@google.com>,
"H . Peter Anvin" <hpa@zytor.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
"Andrey Konovalov" <andreyknvl@google.com>,
"Andrey Ryabinin" <aryabinin@virtuozzo.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Borislav Petkov" <bp@alien8.de>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Christoph Lameter" <cl@linux.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"David Rientjes" <rientjes@google.com>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Eric Dumazet" <edumazet@google.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Hillf Danton" <hdanton@sina.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Jonathan Cameron" <Jonathan.Cameron@huawei.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Joonsoo Kim" <iamjoonsoo.kim@lge.com>,
"Jörn Engel" <joern@purestorage.com>,
"Kees Cook" <keescook@chromium.org>,
"Mark Rutland" <mark.rutland@arm.com>,
"Pekka Enberg" <penberg@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"SeongJae Park" <sjpark@amazon.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Vlastimil Babka" <vbabka@suse.cz>,
"Will Deacon" <will@kernel.org>,
"the arch/x86 maintainers" <x86@kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
"kernel list" <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH v6 6/9] kfence, kasan: make KFENCE compatible with KASAN
Date: Fri, 30 Oct 2020 16:19:34 +0100 [thread overview]
Message-ID: <CANpmjNPoQkWuV0q3atamrAzyOxR9ZTpY43Ndg5+ko0KJhYt9sA@mail.gmail.com> (raw)
In-Reply-To: <CAG48ez30tzadrtJm_ShY8oGjnYpf3GDfcajm7S0xX6UxfTCQZw@mail.gmail.com>
On Fri, 30 Oct 2020 at 16:09, Jann Horn <jannh@google.com> wrote:
>
> On Fri, Oct 30, 2020 at 2:46 PM Marco Elver <elver@google.com> wrote:
> > On Fri, 30 Oct 2020 at 03:50, Jann Horn <jannh@google.com> wrote:
> > > On Thu, Oct 29, 2020 at 2:17 PM Marco Elver <elver@google.com> wrote:
> > > > We make KFENCE compatible with KASAN for testing KFENCE itself. In
> > > > particular, KASAN helps to catch any potential corruptions to KFENCE
> > > > state, or other corruptions that may be a result of freepointer
> > > > corruptions in the main allocators.
> > > >
> > > > To indicate that the combination of the two is generally discouraged,
> > > > CONFIG_EXPERT=y should be set. It also gives us the nice property that
> > > > KFENCE will be build-tested by allyesconfig builds.
> > > >
> > > > Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
> > > > Co-developed-by: Marco Elver <elver@google.com>
> > > > Signed-off-by: Marco Elver <elver@google.com>
> > > > Signed-off-by: Alexander Potapenko <glider@google.com>
> > >
> > > Reviewed-by: Jann Horn <jannh@google.com>
> >
> > Thanks!
> >
> > > with one nit:
> > >
> > > [...]
> > > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > > [...]
> > > > @@ -141,6 +142,14 @@ void kasan_unpoison_shadow(const void *address, size_t size)
> > > > */
> > > > address = reset_tag(address);
> > > >
> > > > + /*
> > > > + * We may be called from SL*B internals, such as ksize(): with a size
> > > > + * not a multiple of machine-word size, avoid poisoning the invalid
> > > > + * portion of the word for KFENCE memory.
> > > > + */
> > > > + if (is_kfence_address(address))
> > > > + return;
> > >
> > > It might be helpful if you could add a comment that explains that
> > > kasan_poison_object_data() does not need a similar guard because
> > > kasan_poison_object_data() is always paired with
> > > kasan_unpoison_object_data() - that threw me off a bit at first.
> >
> > Well, KFENCE objects should never be poisoned/unpoisoned because the
> > kasan_alloc and free hooks have a kfence guard, and none of the code
> > in sl*b.c that does kasan_{poison,unpoison}_object_data() should be
> > executed for KFENCE objects.
> >
> > But I just noticed that kernel/scs.c seems to kasan_poison and
> > unpoison objects, and keeps them poisoned for most of the object
> > lifetime.
>
> FWIW, I wouldn't be surprised if other parts of the kernel also ended
> up wanting to have in-object redzones eventually - e.g. inside skb
> buffers, which have a struct skb_shared_info at the end. AFAIU at the
> moment, KASAN can't catch small OOB accesses from these buffers
> because of the following structure.
Sure, and it might also become more interesting with MTE-based KASAN.
But, currently we recommend not to enable generic KASAN+KFENCE,
because it'd be redundant if the instrumentation price for generic (or
SW-tag) KASAN is already paid. The changes here are also mostly for
testing KFENCE itself.
That may change with MTE-based KASAN, however, which may have modes
where stack traces aren't collected and having KFENCE to get
actionable debug-info across a fleet of machines may still be wanted.
But that story is still evolving. The code here is only for the
generic and SW-tag based KASAN modes, and MTE will have its own
kasan_{un,}poison_shadow (afaik it's being renamed to
kasan_{un,}poison_memory) which works just fine with KFENCE AFAIK.
> > I think we better add a kfence guard to
> > kasan_poison_shadow() as well.
>
> Sounds good.
next prev parent reply other threads:[~2020-10-30 15:19 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-29 13:16 [PATCH v6 0/9] KFENCE: A low-overhead sampling-based memory safety error detector Marco Elver
2020-10-29 13:16 ` [PATCH v6 1/9] mm: add Kernel Electric-Fence infrastructure Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 19:16 ` Marco Elver
2020-10-29 13:16 ` [PATCH v6 2/9] x86, kfence: enable KFENCE for x86 Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 13:00 ` Marco Elver
2020-10-30 15:22 ` Jann Horn
2020-10-29 13:16 ` [PATCH v6 3/9] arm64, kfence: enable KFENCE for ARM64 Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 16:00 ` Mark Rutland
2020-10-30 15:47 ` Mark Rutland
2020-10-30 15:54 ` Marco Elver
2020-10-29 13:16 ` [PATCH v6 4/9] mm, kfence: insert KFENCE hooks for SLAB Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 15:41 ` Marco Elver
2020-10-29 13:16 ` [PATCH v6 5/9] mm, kfence: insert KFENCE hooks for SLUB Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-29 13:16 ` [PATCH v6 6/9] kfence, kasan: make KFENCE compatible with KASAN Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 13:46 ` Marco Elver
2020-10-30 15:08 ` Jann Horn
2020-10-30 15:19 ` Marco Elver [this message]
2020-10-29 13:16 ` [PATCH v6 7/9] kfence, Documentation: add KFENCE documentation Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 9:59 ` Alexander Potapenko
2020-10-29 13:16 ` [PATCH v6 8/9] kfence: add test suite Marco Elver
2020-10-30 2:49 ` Jann Horn
2020-10-30 10:50 ` Marco Elver
2020-10-29 13:16 ` [PATCH v6 9/9] MAINTAINERS: Add entry for KFENCE Marco Elver
2020-10-30 2:50 ` Jann Horn
2020-10-30 2:49 ` [PATCH v6 0/9] KFENCE: A low-overhead sampling-based memory safety error detector Jann Horn
2020-10-30 10:56 ` Marco Elver
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CANpmjNPoQkWuV0q3atamrAzyOxR9ZTpY43Ndg5+ko0KJhYt9sA@mail.gmail.com \
--to=elver@google.com \
--cc=Jonathan.Cameron@huawei.com \
--cc=akpm@linux-foundation.org \
--cc=andreyknvl@google.com \
--cc=aryabinin@virtuozzo.com \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=cl@linux.com \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=dvyukov@google.com \
--cc=edumazet@google.com \
--cc=glider@google.com \
--cc=gregkh@linuxfoundation.org \
--cc=hdanton@sina.com \
--cc=hpa@zytor.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=jannh@google.com \
--cc=joern@purestorage.com \
--cc=kasan-dev@googlegroups.com \
--cc=keescook@chromium.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=paulmck@kernel.org \
--cc=penberg@kernel.org \
--cc=peterz@infradead.org \
--cc=rientjes@google.com \
--cc=sjpark@amazon.com \
--cc=tglx@linutronix.de \
--cc=vbabka@suse.cz \
--cc=will@kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).