Re: [v3 PATCH 5/5] RISC-V: Add EFI stub support.

[Ard Biesheuvel <ardb@kernel.org>]

On Sat, 18 Apr 2020 at 12:51, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Sat, 18 Apr 2020 at 05:03, Atish Patra <atishp@atishpatra.org> wrote:
> >
> > On Thu, Apr 16, 2020 at 12:41 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > On Wed, 15 Apr 2020 at 21:54, 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 +
> > > >  arch/riscv/include/asm/efi.h              |  44 +++++++++
> > > >  drivers/firmware/efi/Kconfig              |   2 +-
> > > >  drivers/firmware/efi/libstub/Makefile     |   7 ++
> > > >  drivers/firmware/efi/libstub/riscv-stub.c | 111 ++++++++++++++++++++++
> > > >  7 files changed, 185 insertions(+), 1 deletion(-)
> > > >  create mode 100644 arch/riscv/include/asm/efi.h
> > > >  create mode 100644 drivers/firmware/efi/libstub/riscv-stub.c
> > > >
> > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > index f39e326a7a42..eb4f41c8f3ce 100644
> > > > --- a/arch/riscv/Kconfig
> > > > +++ b/arch/riscv/Kconfig
> > > > @@ -379,10 +379,30 @@ 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_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 fb6e37db836d..079435804d6d 100644
> > > > --- a/arch/riscv/Makefile
> > > > +++ b/arch/riscv/Makefile
> > > > @@ -80,6 +80,7 @@ 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 4da4886246a4..ae69e12d306a 100644
> > > > --- a/arch/riscv/configs/defconfig
> > > > +++ b/arch/riscv/configs/defconfig
> > > > @@ -129,3 +129,4 @@ CONFIG_DEBUG_BLOCK_EXT_DEVT=y
> > > >  # CONFIG_RUNTIME_TESTING_MENU is not set
> > > >  CONFIG_MEMTEST=y
> > > >  # CONFIG_SYSFS_SYSCALL is not set
> > > > +CONFIG_EFI=y
> > > > diff --git a/arch/riscv/include/asm/efi.h b/arch/riscv/include/asm/efi.h
> > > > new file mode 100644
> > > > index 000000000000..62d7d5eafed8
> > > > --- /dev/null
> > > > +++ b/arch/riscv/include/asm/efi.h
> > > > @@ -0,0 +1,44 @@
> > > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > > +/*
> > > > + * Copyright (C) 2020 Western Digital Corporation or its affiliates.
> > > > + * Based on arch/arm64/include/asm/efi.h
> > > > + */
> > > > +#ifndef _ASM_EFI_H
> > > > +#define _ASM_EFI_H
> > > > +
> > > > +#include <asm/io.h>
> > > > +#include <asm/mmu_context.h>
> > > > +#include <asm/ptrace.h>
> > > > +#include <asm/tlbflush.h>
> > > > +
> > > > +#define VA_BITS_MIN 39
> > > > +
> > > > +/* on RISC-V, the FDT may be located anywhere in system RAM */
> > > > +static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
> > > > +{
> > > > +       return ULONG_MAX;
> > > > +}
> > > > +
> > > > +/* Load initrd at enough distance from DRAM start */
> > > > +static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
> > > > +                                                   unsigned long image_addr)
> > > > +{
> > > > +       return dram_base + SZ_256M;
> > > > +}
> > > > +
> > > > +#define efi_bs_call(func, ...) efi_system_table()->boottime->func(__VA_ARGS__)
> > > > +#define efi_rt_call(func, ...) efi_system_table()->runtime->func(__VA_ARGS__)
> > > > +#define efi_is_native()                (true)
> > > > +
> > > > +#define efi_table_attr(inst, attr)     (inst->attr)
> > > > +
> > > > +#define efi_call_proto(inst, func, ...) inst->func(inst, ##__VA_ARGS__)
> > > > +
> > > > +#define alloc_screen_info(x...)                (&screen_info)
> > > > +extern char stext_offset[];
> > > > +
> > > > +static inline void free_screen_info(struct screen_info *si)
> > > > +{
> > > > +}
> > > > +
> > > > +#endif /* _ASM_EFI_H */
> > > > diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
> > > > index 2a2b2b96a1dc..fcdc789d3f87 100644
> > > > --- a/drivers/firmware/efi/Kconfig
> > > > +++ b/drivers/firmware/efi/Kconfig
> > > > @@ -111,7 +111,7 @@ config EFI_GENERIC_STUB
> > > >
> > > >  config EFI_ARMSTUB_DTB_LOADER
> > > >         bool "Enable the DTB loader"
> > > > -       depends on EFI_GENERIC_STUB
> > > > +       depends on EFI_GENERIC_STUB && !RISCV
> > > >         default y
> > > >         help
> > > >           Select this config option to add support for the dtb= command
> > > > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > > > index 2b4e09bf987c..7d46b70b51f2 100644
> > > > --- a/drivers/firmware/efi/libstub/Makefile
> > > > +++ b/drivers/firmware/efi/libstub/Makefile
> > > > @@ -22,6 +22,8 @@ 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-$(CONFIG_EFI_GENERIC_STUB)      += -I$(srctree)/scripts/dtc/libfdt
> > > >
> > > > @@ -57,6 +59,7 @@ lib-$(CONFIG_EFI_GENERIC_STUB)                += efi-stub.o fdt.o string.o \
> > > >  lib-$(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=$(TEXT_OFFSET)
> > > >
> > > > @@ -81,6 +84,10 @@ STUBCOPY_FLAGS-$(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..69d13e0ebaea
> > > > --- /dev/null
> > > > +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> > > > @@ -0,0 +1,111 @@
> > > > +// 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.
> > > > + */
> >
> > Fixed the comment.
> >
> > > > +#ifdef CONFIG_64BIT
> > > > +#define MIN_KIMG_ALIGN SZ_2M
> > > > +#else
> > > > +#define MIN_KIMG_ALIGN SZ_4M
> > > > +#endif
> > > > +
> > > > +typedef __attribute__((noreturn)) void (*jump_kernel_func)(unsigned int,
> > > > +                                                          unsigned long);
> > > > +efi_status_t check_platform_features(void)
> > > > +{
> > > > +       return EFI_SUCCESS;
> > > > +}
> > > > +
> > > > +static u32 get_boot_hartid_from_fdt(unsigned long fdt)
> > > > +{
> > > > +       int chosen_node, len;
> > > > +       const fdt32_t *prop;
> > > > +
> > > > +       chosen_node = fdt_path_offset((void *)fdt, "/chosen");
> > > > +       if (chosen_node < 0)
> > > > +               return U32_MAX;
> > > > +       prop = fdt_getprop((void *)fdt, chosen_node, "boot-hartid", &len);
> > > > +       if (!prop || len != sizeof(u32))
> > > > +               return U32_MAX;
> > > > +
> > > > +       return fdt32_to_cpu(*prop);
> > > > +}
> > > > +
> > > > +/*
> > > > + * 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,
> > > > +                                unsigned long fdt_size)
> > > > +{
> > > > +       unsigned long kernel_entry = entrypoint + (unsigned long)stext_offset;
> > > > +       jump_kernel_func jump_kernel = (jump_kernel_func) kernel_entry;
> > > > +       u32 hartid = get_boot_hartid_from_fdt(fdt);
> > > > +
> > > > +       if (hartid == U32_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 max_alloc_address;
> > > > +
> > > > +       if (image->image_base != _start)
> > > > +               pr_efi_err("FIRMWARE BUG: efi_loaded_image_t::image_base has bogus value\n");
> > > > +
> > >
> > > I don't think you need this.
> > >
> >
> > Sure. I will remove it. I guess ARM64 code has the error print for
> > legacy loader code ?
> >
>
> No, for broken distro versions of GRUB
>
> > > > +       kernel_size = _edata - _start;
> > > > +       kernel_memsize = kernel_size + (_end - _edata);
> > > > +       max_alloc_address = round_up(dram_base, MIN_KIMG_ALIGN) +
> > > > +                           kernel_memsize;
> > > > +
> > >
> > > You said the kernel could be anywhere in memory, as long as it is
> > > aligned correctly, right?
> >
> > Sorry I was wrong about this. RISC-V kernel maps PAGE_OFFSET virtual
> > address to the
> > physical address <xyz> where it is booted. That means memory between
> > dram start and and <xyz> address
> > will be unusable.
> >
>
> OK
>
> > I also realized that the above computing max_address as above also
> > won't work for the following reason.
> > efi_allocate_pages_aligned actually ALIGN_DOWN the max_address. Thus,
> > efi won't find enough
> > free memory in this case if the max_address is computed from the dram_base.
> >
> > Is there an implicit requirement for efi_allocate_pages_aligned or
> > efi_low_alloc_above should be tried in case of failure?
> >
>
> No not really. What ever works for your particular use case is acceptable to me.
>
> > > In that case, you don't need this, you can simply pass ULONG_MAX as
> > > the max address.
> > >
> > As RISC-V should allocate memory as low as possible to avoid memory
> > wastage, I think the following should work.
> >
> > efi_low_alloc_above(*reserve_size, MIN_KIMG_ALIGN, reserve_addr, dram_base);
> >
> > If this looks okay to you, efi_low_alloc_above should be moved back to
> > mem.c from relocate.c.
> > Should I do it in a separate patch or the original patch should be
> > modified so that efi_low_alloc_above was never moved to relocate.c
> >
>
> No, please keep efi_low_alloc_above() where it is, but drop the
> static, and put back the declaration in efistub.h
>

Alternatively, can you check whether efi_relocate_kernel() already
does what you need?