linux-kernel - Re: [PATCH v6 3/9] arm64, kfence: enable KFENCE for ARM64

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Message-ID: <20201030160004.GE50718@C02TD0UTHF1T.local>
Date:   Fri, 30 Oct 2020 16:00:04 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Marco Elver <elver@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        "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>,
        Dmitry 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>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, joern@...estorage.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>,
        Will Deacon <will@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v6 3/9] arm64, kfence: enable KFENCE for ARM64

On Fri, Oct 30, 2020 at 03:49:26AM +0100, Jann Horn wrote:
> On Thu, Oct 29, 2020 at 2:17 PM Marco Elver <elver@...gle.com> wrote:
> > @@ -312,6 +313,9 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr,
> >             "Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
> >                 return;
> >
> > +       if (kfence_handle_page_fault(addr))
> > +               return;
> 
> As in the X86 case, we may want to ensure that this doesn't run for
> permission faults, only for non-present pages. Maybe move this down
> into the third branch of the "if" block below (neither permission
> fault nor NULL deref)?

I think that'd make sense. Those cases *should* be mutually exclusive,
but it'd be more robust to do the KFENCE checks in that last block so
that if something goes wrong wrong within KFENCE we can't get stuck in a
loop failing to service an instruction abort or similar.

Either that, or factor out an is_el1_translation_fault() and only do the
KFENCE check and is_spurious_el1_translation_fault() check under that.

Thanks,
Mark.