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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Mon, 23 May 2022 16:41:58 +0200
Message-ID: <CAMj1kXE_xc4FvdOLqfK+awqTqoGje=Gy7bmVUFTZY_hjw1K9=w@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>,
        Peter Zijlstra <peterz@infradead.org>,
        Joerg Roedel <jroedel@suse.de>, songmuchun@bytedance.com,
        macro@orcam.me.uk, Frederic Weisbecker <frederic@kernel.org>,
        W_Armin@gmx.de, John Garry <john.garry@huawei.com>,
        Sean Christopherson <seanjc@google.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
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On Mon, 23 May 2022 at 03:18, mawupeng <mawupeng1@huawei.com> wrote:
>
>
>
> =E5=9C=A8 2022/5/20 14:52, Ard Biesheuvel =E5=86=99=E9=81=93:
> > 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_p=
ages)
> >>>     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.
> >
> > But the bottom line is that UEFI should expose the ability to target
> > mirrored memory, hacking around it like this is not a sustainable
> > approach.
>
> Since firmware is responsible for put kernel static image into mirrored
> region and kernel is responsible for relocate this image into mirrored
> region if kaslr is enabled. There is no conflict between these two.
>
> Can we integrate the kernel part(introduce mirrored support to arm64) fir=
st?
>

Yes. If you drop the changes related to fake memmap and rebase, please
resend them after -rc1 is released.