linux-kernel - Re: [PATCH v4 02/11] x86, kfence: enable KFENCE for x86

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Date:   Fri, 2 Oct 2020 08:08:53 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Marco Elver <elver@...gle.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>, Jonathan.Cameron@...wei.com,
        Jonathan Corbet <corbet@....net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, 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>,
        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 v4 02/11] x86, kfence: enable KFENCE for x86

On Tue, Sep 29, 2020 at 3:38 PM Marco Elver <elver@...gle.com> wrote:
> Add architecture specific implementation details for KFENCE and enable
> KFENCE for the x86 architecture. In particular, this implements the
> required interface in <asm/kfence.h> for setting up the pool and
> providing helper functions for protecting and unprotecting pages.
[...]
> diff --git a/arch/x86/include/asm/kfence.h b/arch/x86/include/asm/kfence.h
[...]
> +/* Protect the given page and flush TLBs. */
> +static inline bool kfence_protect_page(unsigned long addr, bool protect)
> +{
[...]
> +       flush_tlb_one_kernel(addr);

flush_tlb_one_kernel() -> flush_tlb_one_user() ->
__flush_tlb_one_user() -> native_flush_tlb_one_user() only flushes on
the local CPU core, not on others. If you want to leave it this way, I
think this needs a comment explaining why we're not doing a global
flush (locking context / performance overhead / ... ?).