Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200921132611.1700350-1-elver@google.com> <20200921132611.1700350-4-elver@google.com>
 <20200921143059.GO2139@willie-the-truck> <CAG_fn=WKaY9MVmbpkgoN4vaJYD_T_A3z2Lgqn+2o8-irmCKywg@mail.gmail.com>
 <CAG_fn=XV7JfJDK+t1X6bnV6gRoiogNXsHfww0jvcEtJ2WZpR7Q@mail.gmail.com>
 <20200921174357.GB3141@willie-the-truck> <CANpmjNNdGWoY_FcqUDUZ2vXy840H2+LGzN3WWrK8iERTKntSTw@mail.gmail.com>
 <20200929135355.GA53442@C02TD0UTHF1T.local>
In-Reply-To: <20200929135355.GA53442@C02TD0UTHF1T.local>
From:   Alexander Potapenko <glider@google.com>
Date:   Tue, 29 Sep 2020 18:52:11 +0200
Message-ID: <CAG_fn=UzvZfOzKEnc_ouqchNcg359yhykKc3tDTYdPhMAQooSQ@mail.gmail.com>
Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Marco Elver <elver@google.com>, Will Deacon <will@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christoph Lameter <cl@linux.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dmitriy Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hillf Danton <hdanton@sina.com>,
        Ingo Molnar <mingo@redhat.com>, Jann Horn <jannh@google.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        SeongJae Park <sjpark@amazon.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vlastimil Babka <vbabka@suse.cz>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

> > 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?