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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Fri, 20 May 2022 08:52:27 +0200
Message-ID: <CAMj1kXFP9kA_rJ8DfP1Ln=W++xL1Rvdojb8ZuNLoOJx2mLkysA@mail.gmail.com>
Subject: Re: [PATCH 0/2] Add support to relocate kernel image to mirrored region
To:     mawupeng <mawupeng1@huawei.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        Mike Rapoport <rppt@kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
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        macro@orcam.me.uk, Frederic Weisbecker <frederic@kernel.org>,
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On Fri, 20 May 2022 at 08:52, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Thu, 19 May 2022 at 13:09, mawupeng <mawupeng1@huawei.com> wrote:
> >
> >
> >
> > =E5=9C=A8 2022/5/7 17:28, mawupeng =E5=86=99=E9=81=93:
> > >
> > >
> > > =E5=9C=A8 2022/5/3 17:58, Ard Biesheuvel =E5=86=99=E9=81=93:
> > >> On Tue, 19 Apr 2022 at 08:43, Wupeng Ma <mawupeng1@huawei.com> wrote=
:
> > >>>
> > >>> From: Ma Wupeng <mawupeng1@huawei.com>
> > >>>
> > >>> Now system image will perfer to be located to mirrored regions both=
 KASLR
> > >>> on and off.
> > >>>
> > >>
> > >> Hello Ma Wupeng,
> > >>
> > >> I wonder if we could simplify this as follows:
> > >> - ignore the non-KASLR case for now, and rely on the bootloader  > l=
oad the image into mirrored memory if it exists;
> > >
> > > In grub, memory for static image is allocated via the following path:
> > >
> > > grub_cmd_linux
> > >    kernel =3D grub_malloc(filelen)
> > >    kernel_alloc_addr =3D grub_efi_allocate_any_pages (kernel_alloc_pa=
ges)
> > >    grub_memcpy (kernel_addr, kernel, grub_min(filelen, kernel_size))
> > >     grub_loader_set (grub_linux_boot, grub_linux_unload, 0)
> > >
> > > Can we get memory from mirrored region by the following steps:
> > > 1. get memory map by calling grub_efi_get_memory_map()
> > > 2. iter all memory map to find a suitable mirrored memory area
> > > 3. locate kernel image to this area
> > >
> > > So, if kaslr is not enabled
> > >   - grub will load kernel into mirrored region
> > > else
> > >   - arm64-stub.c will relocate kernel image to mirrored region
> > >
> > > Is this feasible?
> >
> > Is this a feasible proposal to relocate the static kernel image itself
> > into more reliable memory?
> >
>
> I'm not sure, it all depends on the firmware.
>
> When GRUB calls LoadImage(), the firmware will reallocate the image
> and unpack it there. So it is really the firmware's job to ensure that
> the image is loaded into a suitable location.
>
> I have some code here that implements a EFI based decompressor, and
> which loads the kernel image into mirrored memory if it exists,
> without the need to move it again. It could trivially be modified to
> deal with non-randomized loads as well.
>

Code is here
https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/log/?h=3Defi=
-decompressor-v2