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

[Atish Patra <Atish.Patra@wdc.com>]

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 ?

> 
> 
> > > > +#define TEXT_OFFSET MIN_KIMG_ALIGN
> > > > +
> > > > +typedef __attribute__((noreturn)) void
> > > > (*jump_kernel_func)(unsigned int,
> > > > +                                                          unsi
> > > > gned
> > > > long);
> > > > +
> > > > +efi_status_t check_platform_features(void)
> > > > +{
> > > > +       return EFI_SUCCESS;
> > > > +}
> > > > +
> > > > +u64 get_boot_hartid_from_fdt(unsigned long fdt)
> > > 
> > > static
> > > 
> > > > +{
> > > > +       int chosen_node, len;
> > > > +       const fdt64_t *prop;
> > > > +       uint64_t hartid = U64_MAX;
> > > > +
> > > > +       chosen_node = fdt_path_offset((void *)fdt, "/chosen");
> > > > +       if (chosen_node < 0)
> > > > +               return hartid;
> > > 
> > > Just return U64_MAX here
> > > 
> > > > +       prop = fdt_getprop((void *)fdt, chosen_node, "efi-boot-
> > > > hartid", &len);
> > > 
> > > Please call this 'boot-hartid' not 'efi-boot-hartid' as the
> > > hartid
> > > value is independent of whether you boot via EFI or not.
> > > 
> > > > +       if (!prop || len != sizeof(u64))
> > > > +               return hartid;
> > > > +
> > > 
> > > Return U64_MAX
> > > 
> > > > +       hartid = fdt64_to_cpu(*prop);
> > > > +
> > > 
> > > and just return the swabbed value, so you can get rid of the
> > > local
> > > var.
> > > 
> > 
> > Fixed all the above issues. I changed it to u32 as u64 won't work
> > on 32
> > bit systems.
> > 
> 
> If the hart id is only 32 bits max then i guess that will work.
> 
> > > > +       return hartid;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Jump to real kernel here with following constraints.
> > > > + * 1. MMU should be disabled.
> > > > + * 2. a0 should contain hartid
> > > > + * 3. a1 should DT address
> > > > + */
> > > > +void __noreturn efi_enter_kernel(unsigned long entrypoint,
> > > > unsigned long fdt)
> > > 
> > > This prototype has changed, and now includes the size of the fdt
> > > in
> > > param 3.
> > > 
> > 
> > Ahh yes. Fixed.
> > 
> > > > +{
> > > > +       unsigned long kernel_entry = entrypoint + _start_kernel
> > > > -
> > > > _start;
> > > 
> > > stext_offset ? It has a terrible name though, and I'll probably
> > > propose to change it at some point, for all arches. But you can
> > > still
> > > use it here.
> > > 
> > 
> > Sure. I updated it with stext_offset.
> > 
> > > > +       jump_kernel_func jump_kernel = (void (*)(unsigned int,
> > > > unsigned long))kernel_entry;
> > > > +       u64 hartid = get_boot_hartid_from_fdt(fdt);
> > > > +
> > > > +       if (hartid == U64_MAX)
> > > > +               /* We can not use panic or BUG at this point */
> > > > +               __asm__ __volatile__ ("ebreak");
> > > > +       /* Disable MMU */
> > > > +       csr_write(CSR_SATP, 0);
> > > > +       jump_kernel(hartid, fdt);
> > > > +}
> > > > +
> > > > +efi_status_t handle_kernel_image(unsigned long *image_addr,
> > > > +                                unsigned long *image_size,
> > > > +                                unsigned long *reserve_addr,
> > > > +                                unsigned long *reserve_size,
> > > > +                                unsigned long dram_base,
> > > > +                                efi_loaded_image_t *image)
> > > > +{
> > > > +       efi_status_t status;
> > > > +       unsigned long kernel_size, kernel_memsize = 0;
> > > > +       unsigned long preferred_offset;
> > > > +
> > > > +       /*
> > > > +        * The preferred offset of the kernel Image is
> > > > TEXT_OFFSET
> > > > bytes beyond
> > > > +        * a KIMG_ALIGN aligned base.
> > > > +        */
> > > > +       preferred_offset = round_up(dram_base, MIN_KIMG_ALIGN)
> > > > +
> > > > TEXT_OFFSET;
> > > > +
> > > > +       kernel_size = _edata - _start;
> > > > +       kernel_memsize = kernel_size + (_end - _edata);
> > > > +
> > > > +       /*
> > > > +        * Try a straight allocation at the preferred offset.
> > > > +        * This will work around the issue where, if dram_base
> > > > ==
> > > > 0x0,
> > > > +        * efi_low_alloc() refuses to allocate at 0x0 (to
> > > > prevent
> > > > the
> > > > +        * address of the allocation to be mistaken for a FAIL
> > > > return
> > > > +        * value or a NULL pointer). It will also ensure that,
> > > > on
> > > > +        * platforms where the [dram_base, dram_base +
> > > > TEXT_OFFSET)
> > > > +        * interval is partially occupied by the firmware (like
> > > > on
> > > > APM
> > > > +        * Mustang), we can still place the kernel at the
> > > > address
> > > > +        * 'dram_base + TEXT_OFFSET'.
> > > 
> > > Better drop this entire last sentence (unless it is relevant, but
> > > then
> > > rework it to drop the APM Mustang reference)
> > > 
> > 
> > As stated above, RISC-V firmware occupies [dram_base, dram_base +
> > 128K). That's why I thought this comment is useful. I should have
> > removed the mustand reference. I will update it.
> > 
> > > > +        */
> > > > +       if (*image_addr == preferred_offset)
> > > > +               return EFI_SUCCESS;
> > > > +
> > > > +       *image_addr = *reserve_addr = preferred_offset;
> > > > +       *reserve_size = round_up(kernel_memsize,
> > > > EFI_ALLOC_ALIGN);
> > > > +
> > > > +       status = efi_bs_call(allocate_pages,
> > > > EFI_ALLOCATE_ADDRESS,
> > > > +                               EFI_LOADER_DATA,
> > > > +                               *reserve_size / EFI_PAGE_SIZE,
> > > > +                               (efi_physical_addr_t
> > > > *)reserve_addr);
> > > > +
> > > > +       if (status != EFI_SUCCESS) {
> > > > +               *reserve_size = kernel_memsize + TEXT_OFFSET;
> > > > +               status = efi_low_alloc(*reserve_size,
> > > > MIN_KIMG_ALIGN,
> > > > +                                      reserve_addr);
> > > > +
> > > > +               if (status != EFI_SUCCESS) {
> > > > +                       pr_efi_err("Failed to relocate
> > > > kernel\n");
> > > > +                       *reserve_size = 0;
> > > > +                       return status;
> > > > +               }
> > > > +               *image_addr = *reserve_addr + TEXT_OFFSET;
> > > > +       }
> > > > +       memcpy((void *)*image_addr, image->image_base,
> > > > kernel_size);
> > > > +
> > > > +       return EFI_SUCCESS;
> > > > +}
> > > > --
> > > > 2.24.0
> > > > 
> > 
> > --
> > Regards,
> > Atish

-- 
Regards,
Atish