linux-kernel - Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CANpmjNOg2OeWpXn57_ikqv4KR0xVEooCDECUyRijgr0tt4+Ncw@mail.gmail.com>
Date:   Wed, 14 Oct 2020 21:12:37 +0200
From:   Marco Elver <elver@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Lameter <cl@...ux.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hillf Danton <hdanton@...a.com>,
        Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        SeongJae Park <sjpark@...zon.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64

On Thu, 8 Oct 2020 at 12:45, Mark Rutland <mark.rutland@....com> wrote:
> On Thu, Oct 08, 2020 at 11:40:52AM +0200, Marco Elver wrote:
> > On Thu, 1 Oct 2020 at 19:58, Mark Rutland <mark.rutland@....com> wrote:
> > [...]
> > > > > If you need virt_to_page() to work, the address has to be part of the
> > > > > linear/direct map.
> > [...]
> > >
> > > What's the underlying requirement here? Is this a performance concern,
> > > codegen/codesize, or something else?
> >
> > It used to be performance, since is_kfence_address() is used in the
> > fast path. However, with some further tweaks we just did to
> > is_kfence_address(), our benchmarks show a pointer load can be
> > tolerated.
>
> Great!
>
> I reckon that this is something we can optimize in futue if necessary
> (e.g. with some form of code-patching for immediate values), but it's
> good to have a starting point that works everywhere!
>
> [...]
>
> > > I'm not too worried about allocating this dynamically, but:
> > >
> > > * The arch code needs to set up the translation tables for this, as we
> > >   cannot safely change the mapping granularity live.
> > >
> > > * As above I'm fairly certain x86 needs to use a carevout from the
> > >   linear map to function correctly anyhow, so we should follow the same
> > >   approach for both arm64 and x86. That might be a static carevout that
> > >   we figure out the aliasing for, or something entirely dynamic.
> >
> > We're going with dynamically allocating the pool (for both x86 and
> > arm64), since any benefits we used to measure from the static pool are
> > no longer measurable (after removing a branch from
> > is_kfence_address()). It should hopefully simplify a lot of things,
> > given all the caveats that you pointed out.
> >
> > For arm64, the only thing left then is to fix up the case if the
> > linear map is not forced to page granularity.
>
> The simplest way to do this is to modify arm64's arch_add_memory() to
> force the entire linear map to be mapped at page granularity when KFENCE
> is enabled, something like:
>
[...]
>
> ... and I given that RODATA_FULL_DEFAULT_ENABLED is the default, I
> suspect it's not worth trying to only for that for the KFENCE region
> unless someone complains.

We've got most of this sorted now for v5 -- thank you!

The only thing we're wondering now, is if there are any corner cases
with using memblock_alloc'd memory for the KFENCE pool? (We'd like to
avoid page alloc's MAX_ORDER limit.) We have a version that passes
tests on x86 and arm64, but checking just in case. :-)

Thanks,
-- Marco