linux-hardening - Re: [PATCH v2 14/16] kasan: Remove ksize()-related tests

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Date:   Sun, 25 Sep 2022 17:38:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        "Ruhl, Michael J" <michael.j.ruhl@...el.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alex Elder <elder@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Daniel Micay <danielmicay@...il.com>,
        Yonghong Song <yhs@...com>, Marco Elver <elver@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-fsdevel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org, dev@...nvswitch.org,
        x86@...nel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 14/16] kasan: Remove ksize()-related tests

On Sat, Sep 24, 2022 at 10:15:18AM +0200, Dmitry Vyukov wrote:
> On Fri, 23 Sept 2022 at 22:28, Kees Cook <keescook@...omium.org> wrote:
> >
> > In preparation for no longer unpoisoning in ksize(), remove the behavioral
> > self-tests for ksize().
> >
> > [...]
> > -/* Check that ksize() makes the whole object accessible. */
> > -static void ksize_unpoisons_memory(struct kunit *test)
> > -{
> > -       char *ptr;
> > -       size_t size = 123, real_size;
> > -
> > -       ptr = kmalloc(size, GFP_KERNEL);
> > -       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> > -       real_size = ksize(ptr);
> > -
> > -       OPTIMIZER_HIDE_VAR(ptr);
> > -
> > -       /* This access shouldn't trigger a KASAN report. */
>  > -       ptr[size] = 'x';
> 
> I would rather keep the tests and update to the new behavior. We had
> bugs in ksize, we need test coverage.
> I assume ptr[size] access must now produce an error even after ksize.

Good point on all these! I'll respin.

-- 
Kees Cook