Re: [RFC PATCH 5/5] RISC-V: Add EFI stub support.

[Atish Patra <atishp@atishpatra.org>]

On Thu, Feb 27, 2020 at 10:57 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Fri, 28 Feb 2020 at 02:05, Atish Patra <Atish.Patra@wdc.com> wrote:
> >
> > On Thu, 2020-02-27 at 20:59 +0100, Ard Biesheuvel wrote:
> > > On Thu, 27 Feb 2020 at 20:53, Atish Patra <Atish.Patra@wdc.com>
> > > wrote:
> > > > On Wed, 2020-02-26 at 08:28 +0100, Ard Biesheuvel wrote:
> > > > > On Wed, 26 Feb 2020 at 02:10, Atish Patra <atish.patra@wdc.com>
> > > > > wrote:
> > > > > > Add a RISC-V architecture specific stub code that actually
> > > > > > copies
> > > > > > the
> > > > > > actual kernel image to a valid address and jump to it after
> > > > > > boot
> > > > > > services
> > > > > > are terminated. Enable UEFI related kernel configs as well for
> > > > > > RISC-V.
> > > > > >
> > > > > > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > > > > > ---
> > > > > >  arch/riscv/Kconfig                        |  20 ++++
> > > > > >  arch/riscv/Makefile                       |   1 +
> > > > > >  arch/riscv/configs/defconfig              |   1 +
> > > > > >  drivers/firmware/efi/libstub/Makefile     |   8 ++
> > > > > >  drivers/firmware/efi/libstub/riscv-stub.c | 135
> > > > > > ++++++++++++++++++++++
> > > > > >  5 files changed, 165 insertions(+)
> > > > > >  create mode 100644 drivers/firmware/efi/libstub/riscv-stub.c
> > > > > >
> > > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > > > index 42c122170cfd..68b1d565e51d 100644
> > > > > > --- a/arch/riscv/Kconfig
> > > > > > +++ b/arch/riscv/Kconfig
> > > > > > @@ -372,10 +372,30 @@ config CMDLINE_FORCE
> > > > > >
> > > > > >  endchoice
> > > > > >
> > > > > > +config EFI_STUB
> > > > > > +       bool
> > > > > > +
> > > > > > +config EFI
> > > > > > +       bool "UEFI runtime support"
> > > > > > +       depends on OF
> > > > > > +       select LIBFDT
> > > > > > +       select UCS2_STRING
> > > > > > +       select EFI_PARAMS_FROM_FDT
> > > > > > +       select EFI_STUB
> > > > > > +       select EFI_GENERIC_ARCH_STUB
> > > > > > +       default y
> > > > > > +       help
> > > > > > +         This option provides support for runtime services
> > > > > > provided
> > > > > > +         by UEFI firmware (such as non-volatile variables,
> > > > > > realtime
> > > > > > +          clock, and platform reset). A UEFI stub is also
> > > > > > provided
> > > > > > to
> > > > > > +         allow the kernel to be booted as an EFI application.
> > > > > > This
> > > > > > +         is only useful on systems that have UEFI firmware.
> > > > > > +
> > > > > >  endmenu
> > > > > >
> > > > > >  menu "Power management options"
> > > > > >
> > > > > >  source "kernel/power/Kconfig"
> > > > > > +source "drivers/firmware/Kconfig"
> > > > > >
> > > > > >  endmenu
> > > > > > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > > > > > index b9009a2fbaf5..0afaa89ba9ad 100644
> > > > > > --- a/arch/riscv/Makefile
> > > > > > +++ b/arch/riscv/Makefile
> > > > > > @@ -78,6 +78,7 @@ head-y := arch/riscv/kernel/head.o
> > > > > >  core-y += arch/riscv/
> > > > > >
> > > > > >  libs-y += arch/riscv/lib/
> > > > > > +core-$(CONFIG_EFI_STUB) +=
> > > > > > $(objtree)/drivers/firmware/efi/libstub/lib.a
> > > > > >
> > > > > >  PHONY += vdso_install
> > > > > >  vdso_install:
> > > > > > diff --git a/arch/riscv/configs/defconfig
> > > > > > b/arch/riscv/configs/defconfig
> > > > > > index e2ff95cb3390..0a5d3578f51e 100644
> > > > > > --- a/arch/riscv/configs/defconfig
> > > > > > +++ b/arch/riscv/configs/defconfig
> > > > > > @@ -125,3 +125,4 @@ CONFIG_DEBUG_BLOCK_EXT_DEVT=y
> > > > > >  # CONFIG_FTRACE is not set
> > > > > >  # CONFIG_RUNTIME_TESTING_MENU is not set
> > > > > >  CONFIG_MEMTEST=y
> > > > > > +CONFIG_EFI=y
> > > > > > diff --git a/drivers/firmware/efi/libstub/Makefile
> > > > > > b/drivers/firmware/efi/libstub/Makefile
> > > > > > index 2c5b76787126..38facb61745b 100644
> > > > > > --- a/drivers/firmware/efi/libstub/Makefile
> > > > > > +++ b/drivers/firmware/efi/libstub/Makefile
> > > > > > @@ -21,6 +21,8 @@ cflags-$(CONFIG_ARM64)                :=
> > > > > > $(subst
> > > > > > $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > > > >  cflags-$(CONFIG_ARM)           := $(subst
> > > > > > $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > > > >                                    -fno-builtin -fpic \
> > > > > >                                    $(call cc-option,-mno-
> > > > > > single-
> > > > > > pic-base)
> > > > > > +cflags-$(CONFIG_RISCV)         := $(subst
> > > > > > $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > > > > +                                  -fpic
> > > > > >
> > > > > >  cflags-$(CONFIG_EFI_GENERIC_ARCH_STUB) +=
> > > > > > -I$(srctree)/scripts/dtc/libfdt
> > > > > >
> > > > > > @@ -55,6 +57,7 @@ lib-
> > > > > > $(CONFIG_EFI_GENERIC_ARCH_STUB)           +=
> > > > > > efi-stub.o fdt.o string.o \
> > > > > >  lib-$(CONFIG_ARM)              += arm32-stub.o
> > > > > >  lib-$(CONFIG_ARM64)            += arm64-stub.o
> > > > > >  lib-$(CONFIG_X86)              += x86-stub.o
> > > > > > +lib-$(CONFIG_RISCV)            += riscv-stub.o
> > > > > >  CFLAGS_arm32-stub.o            := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > > > > >  CFLAGS_arm64-stub.o            := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > > > > >
> > > > > > @@ -79,6 +82,11 @@ STUBCOPY_FLAGS-$(CONFIG_ARM64)       += --
> > > > > > prefix-alloc-sections=.init \
> > > > > >                                    --prefix-symbols=__efistub_
> > > > > >  STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS
> > > > > >
> > > > > > +STUBCOPY_FLAGS-$(CONFIG_RISCV) += --prefix-alloc-
> > > > > > sections=.init \
> > > > > > +                                  --prefix-symbols=__efistub_
> > > > > > +STUBCOPY_RELOC-$(CONFIG_RISCV) := R_RISCV_HI20
> > > > > > +
> > > > > > +
> > > > > >  $(obj)/%.stub.o: $(obj)/%.o FORCE
> > > > > >         $(call if_changed,stubcopy)
> > > > > >
> > > > > > diff --git a/drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > b/drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > new file mode 100644
> > > > > > index 000000000000..3935b29ea93a
> > > > > > --- /dev/null
> > > > > > +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > @@ -0,0 +1,135 @@
> > > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > > > +/*
> > > > > > + * Copyright (C) 2013, 2014 Linaro Ltd;  <roy.franz@linaro.org
> > > > > > >
> > > > > > + * Copyright (C) 2020 Western Digital Corporation or its
> > > > > > affiliates.
> > > > > > + *
> > > > > > + * This file implements the EFI boot stub for the RISC-V
> > > > > > kernel.
> > > > > > + * Adapted from ARM64 version at
> > > > > > drivers/firmware/efi/libstub/arm64-stub.c.
> > > > > > + */
> > > > > > +
> > > > > > +#include <linux/efi.h>
> > > > > > +#include <linux/libfdt.h>
> > > > > > +#include <linux/libfdt_env.h>
> > > > > > +#include <asm/efi.h>
> > > > > > +#include <asm/sections.h>
> > > > > > +
> > > > > > +#include "efistub.h"
> > > > > > +/*
> > > > > > + * RISCV requires the kernel image to placed TEXT_OFFSET bytes
> > > > > > beyond a 2 MB
> > > > > > + * aligned base for 64 bit and 4MB for 32 bit.
> > > > > > + */
> > > > > > +#if IS_ENABLED(CONFIG_64BIT)
> > > > >
> > > > > You can use #ifdef here
> > > > >
> > > >
> > > > ok.
> > > >
> > > > > > +#define MIN_KIMG_ALIGN SZ_2M
> > > > > > +#else
> > > > > > +#define MIN_KIMG_ALIGN SZ_4M
> > > > > > +#endif
> > > > > > +/*
> > > > > > + * TEXT_OFFSET ensures that we don't overwrite the firmware
> > > > > > that
> > > > > > probably sits
> > > > > > + * at the beginning of the DRAM.
> > > > > > + */
> > > > >
> > > > > Ugh. Really? On an EFI system, that memory should be reserved in
> > > > > some
> > > > > way, we shouldn't be able to stomp on it like that.
> > > > >
> > > >
> > > > Currently, we reserve the initial 128KB for run time firmware(only
> > > > openSBI for now, EDK2 later) by using PMP (physical memory
> > > > protection).
> > > > Any acess to that region from supervisor mode (i.e. U-Boot) will
> > > > result
> > > > in a fault.
> > > >
> > > > Is it mandatory for UEFI to reserve the beginning of the DRAM ?
> > > >
> > >
> > > It is mandatory to describe which memory is usable and which memory
> > > is
> > > reserved. If this memory is not usable, you either describe it as
> > > reserved, or not describe it at all. Describing it as usable memory,
> > > allocating it for the kernel but with a hidden agreement that it is
> > > reserved is highly likely to cause problems down the road.
> > >
> >
> > I completely agree with you on this. We have been talking to have a
> > booting guide and memory map document for RISC-V Linux to document all
> > the idiosyncries of RISC-V. But that has not happend until now.
> > Once, the ordered booting patches are merged, I will try to take a stab
> > at it.
> >
> > Other than that, do we need to describe it somewhere in U-boot wrt to
> > UEFI so that it doesn't allocate memory from that region ?
> >
>
> It is an idiosyncrasy that the firmware should hide from the OS.
>
> What if GRUB comes along and attempts to allocate that memory? Do we
> also have to teach it that the first 128 KB memory of free memory are
> magic and should not be touched?
>
> So the answer is to mark it as reserved. This way, no UEFI tools,
> bootloaders etc will ever try to use it.

Sounds good to me. We are currently discussing the best approach to
provide reserved memory
information to U-Boot/EDK2. The idea is to U-Boot/EDK2 may have to
update the DT with
reserved-memory node so that Linux is aware of the reservation as well.

Then, in the stub, you can
> tweak the existing code to cheat a bit, and make the TEXT_OFFSET
> window overlap the 128 KB reserved window at the bottom of memory.
> Doing that in the stub is fine - this is part of the kernel so it can
> know about crazy RISC-V rules.

I am bit confused here. Why does EFI stub need to overlap the reserved memory.
I thought EFI stub just needs to parse the DT to find out the reserved
memory region to make sure
that it doesn't try to access/overwrite that region.

-- 
Regards,
Atish