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

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Date:   Fri, 30 Oct 2020 16:54:50 +0100
From:   Marco Elver <elver@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     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>, Jann Horn <jannh@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Jörn Engel <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>,
        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 v6 3/9] arm64, kfence: enable KFENCE for ARM64

On Fri, 30 Oct 2020 at 16:47, Mark Rutland <mark.rutland@....com> wrote:
>
> On Thu, Oct 29, 2020 at 02:16:43PM +0100, Marco Elver wrote:
> > Add architecture specific implementation details for KFENCE and enable
> > KFENCE for the arm64 architecture. In particular, this implements the
> > required interface in <asm/kfence.h>.
> >
> > KFENCE requires that attributes for pages from its memory pool can
> > individually be set. Therefore, force the entire linear map to be mapped
> > at page granularity. Doing so may result in extra memory allocated for
> > page tables in case rodata=full is not set; however, currently
> > CONFIG_RODATA_FULL_DEFAULT_ENABLED=y is the default, and the common case
> > is therefore not affected by this change.
> >
> > Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
> > Co-developed-by: Alexander Potapenko <glider@...gle.com>
> > Signed-off-by: Alexander Potapenko <glider@...gle.com>
> > Signed-off-by: Marco Elver <elver@...gle.com>
> > ---
> > v5:
> > * Move generic page allocation code to core.c [suggested by Jann Horn].
> > * Remove comment about HAVE_ARCH_KFENCE_STATIC_POOL, since we no longer
> >   support static pools.
> > * Force page granularity for the linear map [suggested by Mark Rutland].
> > ---
> >  arch/arm64/Kconfig              |  1 +
> >  arch/arm64/include/asm/kfence.h | 19 +++++++++++++++++++
> >  arch/arm64/mm/fault.c           |  4 ++++
> >  arch/arm64/mm/mmu.c             |  7 ++++++-
> >  4 files changed, 30 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/arm64/include/asm/kfence.h
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index f858c352f72a..2f8b32dddd8b 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -135,6 +135,7 @@ config ARM64
> >       select HAVE_ARCH_JUMP_LABEL_RELATIVE
> >       select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
> >       select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN
> > +     select HAVE_ARCH_KFENCE if (!ARM64_16K_PAGES && !ARM64_64K_PAGES)
>
> Why does this depend on the page size?
>
> If this is functional, but has a larger overhead on 16K or 64K, I'd
> suggest removing the dependency, and just updating the Kconfig help text
> to explain that.

Good point, I don't think anything is requiring us to force 4K pages.
Let's remove it.

Thanks,
-- Marco

> Otherwise, this patch looks fine to me.
>
> Thanks,
> Mark.