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

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Date:   Tue, 29 Sep 2020 18:52:11 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Marco Elver <elver@...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 x86 we just do `char __kfence_pool[KFENCE_POOL_SIZE] ...;` to
> > statically allocate the pool. On arm64 this doesn't seem to work
> > because static memory doesn't have struct pages?
>
> Are you using virt_to_page() directly on that statically-allocated
> __kfence_pool? If so you'll need to use lm_alias() if so, as is done in
> mm/kasan/init.c.
>
> Anything statically allocated is part of the kernel image address range
> rather than the linear/direct map, and doesn't have a valid virt addr,
> but its linear map alias does.
>
> If you enable CONFIG_DEBUG_VIRTUAL you should get warnings if missing
> lm_alias() calls.

I just checked that on x86 CONFIG_DEBUG_VIRTUAL prints no warnings on our tests.
virt_addr_valid() also returns true for addresses belonging to
__kfence_pool declared in BSS.
Could this be related to x86 mapping the kernel twice?