linux-kernel - Re: [PATCH] arm64: correct modules range of kernel virtual memory layout

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Date:   Mon, 7 Aug 2017 14:42:13 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Miles Chen <miles.chen@...iatek.com>
Cc:     Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com
Subject: Re: [PATCH] arm64: correct modules range of kernel virtual memory layout

On 7 August 2017 at 14:36, Miles Chen <miles.chen@...iatek.com> wrote:
> On Mon, 2017-08-07 at 14:18 +0100, Ard Biesheuvel wrote:
>> On 7 August 2017 at 14:16, Will Deacon <will.deacon@....com> wrote:
>> > On Mon, Aug 07, 2017 at 07:04:46PM +0800, Miles Chen wrote:
>> >> The commit f80fb3a3d508 ("arm64: add support for kernel ASLR")
>> >> moved module virtual address to
>> >> [module_alloc_base, module_alloc_base + MODULES_VSIZE).
>> >>
>> >> Display module information of the virtual kernel
>> >> memory layout by using module_alloc_base.
>> >>
>> >> testing output:
>> >> 1) Current implementation:
>> >> Virtual kernel memory layout:
>> >>       modules : 0xffffff8000000000 - 0xffffff8008000000   (   128 MB)
>> >> 2) this patch + KASLR:
>> >> Virtual kernel memory layout:
>> >>       modules : 0xffffff8000560000 - 0xffffff8008560000   (   128 MB)
>> >> 3) this patch + KASLR and a dummy seed:
>> >> Virtual kernel memory layout:
>> >>       modules : 0xffffffa7df637000 - 0xffffffa7e7637000   (   128 MB)
>> >>
>> >> Signed-off-by: Miles Chen <miles.chen@...iatek.com>
>> >> ---
>> >>  arch/arm64/mm/init.c | 5 +++--
>> >>  1 file changed, 3 insertions(+), 2 deletions(-)
>> >
>> > Does this mean the modules code in our pt dumper is busted
>> > (arch/arm64/mm/dump.c)? Also, what about KASAN, which uses these addresses
>> > too (in kasan_init)? Should we just remove MODULES_VADDR and MODULES_END
>> > altogether?
>> >
> The module range is not randomized if CONFIG_KASAN is enabled.
> (arch/arm64/kernel/kaslr.c)
>>
>> I don't think we need this patch. The 'module' line simply prints the
>> VA region that is reserved for modules. The fact that we end up
>> putting them elsewhere when running randomized does not necessarily
>> mean this line should reflect that.
>
> The Kernel virtual layout info should be as correct as possible
> or we should remove the "modules line" in the kernel address layout
> since it does not show the correct information.
>

That is your opinion. I disagree.