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

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Message-ID: <20200929140226.GB53442@C02TD0UTHF1T.local>
Date:   Tue, 29 Sep 2020 15:02:26 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Will Deacon <will@...nel.org>, Marco Elver <elver@...gle.com>,
        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@...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>, 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 Fri, Sep 25, 2020 at 05:25:11PM +0200, Alexander Potapenko wrote:
> Will,
> 
> > Given that the pool is relatively small (i.e. when compared with our virtual
> > address space), dedicating an area of virtual space sounds like it makes
> > the most sense here. How early do you need it to be available?
> 
> How do we assign struct pages to a fixed virtual space area (I'm
> currently experimenting with 0xffff7f0000000000-0xffff7f0000200000)?

You don't.

There should be a struct page for each of the /physical/ pages, and
these can be found:

* via the physical address, using phyts_to_page() or pfn_to_page()
* via the linear/direct map, using virt_to_page()
* via the vmalloc page tables using vmalloc_to_page()

If you need virt_to_page() to work, the address has to be part of the
linear/direct map.

If you need to find the struct page for something that's part of the
kernel image you can use virt_to_page(lm_alias(x)).

> Looks like filling page table entries (similarly to what's being done
> in arch/arm64/mm/kasan_init.c) is not enough.
> I thought maybe vmemmap_populate() would do the job, but it didn't
> (virt_to_pfn() still returns invalid PFNs).

As above, I think lm_alias() will solve the problem here. Please see
that and CONFIG_DEBUG_VIRTUAL.

Thanks,
Mark.