[RFC PATCH 0/3] riscv: Add riscv.fwsz kernel parameter to save memory

[Guo Ren]

On Wed, Nov 24, 2021 at 8:15 PM Heiko Stübner <heiko at sntech.de> wrote:
>
> Am Mittwoch, 24. November 2021, 07:49:26 CET schrieb Guo Ren:
> > On Wed, Nov 24, 2021 at 4:01 AM Atish Patra <atishp at atishpatra.org> wrote:
> > >
> > > On Tue, Nov 23, 2021 at 11:33 AM Heiko Stübner <heiko at sntech.de> wrote:
> > > >
> > > > Hi Guo,
> > > >
> > > > Am Dienstag, 23. November 2021, 02:57:14 CET schrieb guoren at kernel.org:
> > > > > From: Guo Ren <guoren at linux.alibaba.com>
> > > > >
> > > > > The firmware of riscv (such as opensbi) occupy 2MB(64bit) /
> > > > > 4MB(32bit) in Linux. It's very wasteful to small memory footprint
> > > > > soc chip such as Allwinner D1s/F133. The kernel parameter gives a
> > > > > chance to users to set the proper size of the firmware and get
> > > > > more than 1.5MB of memory.
> > > >
> > > > is this kernel parameter approach a result of the T-Head Ice-SoC
> > > > currently loading its openSBI from inside the main u-boot via extfs-load,
> > > > directly before the kernel itself [0] ?
> > >
> > > Looking at the defconfig[1], it may be U-Boot SPL not U-Boot proper. I
> > > may be looking at the wrong config though.
> > > If U-Boot SPL is actually used, you don't even need to manually load
> > > OpenSBI "fw_jump" binary.
> > >
> > > As Heiko pointed, you should just follow how U-Boot SPL works on
> > > hifive unmatched (creating the FIT image)
> > > The standard U-Boot SPL uses with fw_dynamic which provides all the
> > > flexibility you want.
> > I've no right to force users' flavor of boot flow.
> >
> > 1) SPL -> opensbi M-mode -> u-boot S-mode -> Linux
> > 2) SPL -> u-boot M-mode -> opensbi M-mode -> Linux
> >
> > All are okay for me. I think the most straightforward reason for
> > people choosing 2) is that they want to try the newest OpenSBI & Linux
> > and 2) is more convenient for replacing.
>
> Though that second option is merely a hack during development.
>
> Having u-boot run in M-mode creates an attack surface that is a lot
> bigger (with it running usb, ethernet and whatnot) compared to shedding
> privileges before that.
>
> I'd consider openSBI as part of the device firmware, so that shouldn't be
> a component you replace daily. Also U-Boot for example already provides
> established ways to sign and verify the parts loaded by SPL, by signing
> the created FIT image this would also include the openSBI image.
>
> So in case (1) you can add more security by simply adding the necessary
> key references during u-boot build, where on the other hand if you _want_
> security in case (2) you're back to hand-rolling any verification
> [with less review and thus more prone to have issues]
>
> Having the _ability_ to verify the loaded firmware components can be a
> requirement in projects, so I think the default should always case (1),
> to not encourage insecure implementations any more than necessary ;-) .
I think nobody would use case (2) in production.

>
>
> Heiko
>
>
> > >
> > > [1] https://github.com/T-head-Semi/u-boot/blob/main/configs/ice_evb_c910_defconfig
> > > >
> > > > Because that approach in general looks not ideal.
> > > >
> > > > Normally you want the main u-boot already running with less privileges
> > > > so firmware like openSBI should've been already loaded before that.
> > > > Even more true when you're employing methods to protect memory regions
> > > > from less privileged access.
> > > >
> > > > A lot of socs set u-boot as opensbi payload, but for the example the D1
> > > > mainline approach uses the Allwinner TOC1 image format to load both
> > > > opensbi and the main uboot into memory from its 1st stage loader.
> > > >
> > > >
> > > > Of course the best way would be to just mimic what a number of
> > > > arm64 and also riscv socs do and use already existing u-boot utilities.
> > > >
> > > > U-Boot can create a FIT image containing both main u-boot, dtb and
> > > > firmware images that all get loaded from SPL and placed at the correct
> > > > addresses before having the SPL jump into opensbi and from there
> > > > into u-boot [1] .
> > > >
> > > > And as Anup was writing, reserved-memory should then be the way
> > > > to go to tell the kernel what regions to omit.
> > > >
> > > > And mainline u-boot has already the means to even take the reserved-memory
> > > > from the devicetree used by opensbi and copy it to a new devicetree,
> > > > if the second one is different.
> > > >
> > > >
> > > > Heiko
> > > >
> > > >
> > > > [0] https://github.com/T-head-Semi/u-boot/blob/main/include/configs/ice-c910.h#L46
> > > > [1] see spl_invoke_opensbi() in common/spl/spl_opensbi.c
> > > > [2] see riscv_board_reserved_mem_fixup() in arch/riscv/lib/fdt_fixup.c
> > > >
> > > > >
> > > > > Guo Ren (3):
> > > > >   riscv: Remove 2MB offset in the mm layout
> > > > >   riscv: Add early_param to decrease firmware region
> > > > >   riscv: Add riscv.fwsz kernel parameter
> > > > >
> > > > >  .../admin-guide/kernel-parameters.txt         |  3 +++
> > > > >  arch/riscv/include/asm/page.h                 |  8 +++++++
> > > > >  arch/riscv/kernel/head.S                      | 10 +++-----
> > > > >  arch/riscv/kernel/vmlinux.lds.S               |  5 ++--
> > > > >  arch/riscv/mm/init.c                          | 23 ++++++++++++++++---
> > > > >  5 files changed, 36 insertions(+), 13 deletions(-)
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > linux-riscv mailing list
> > > > linux-riscv at lists.infradead.org
> > > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > >
> > >
> > >
> > > --
> > > Regards,
> > > Atish
> >
> >
> >
> >
>
>
>
>


--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/