[PATCH] efi: arm-stub: Correct FDT and initrd allocation rules for arm64

[Ard Biesheuvel]

On 9 February 2017 at 10:16, Ard Biesheuvel <ard.biesheuvel at linaro.org> wrote:
> On arm64, we have made some changes over the past year to the way the
> kernel itself is allocated and to how it deals with the initrd and FDT.
> This patch brings the allocation logic in the EFI stub in line with that,
> which is necessary because the introduction of KASLR has created the
> possibility for the initrd to be allocated in a place where the kernel
> may not be able to map it. (This is currently a theoretical scenario,
> since it only affects systems where the size of RAM exceeds the size of
> the linear mapping.)
>

Actually, this affects systems where the RAM /footprint/ exceeds the
size of the linear region, and it isn't that theoretical given that
some Freescale systems were already affected by this in some way. But
we switched to 48-bit VAs by default, and in that configuration, this
issue is unlikely to occur at present.


> So adhere to the arm64 boot protocol, and make sure that the initrd is
> fully inside a 1GB aligned 32 GB window that covers the kernel as well.
>
> The FDT may be anywhere in memory on arm64 now that we map it via the
> fixmap, so we can lift the address restriction there completely.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  arch/arm/include/asm/efi.h              | 14 +++++++++++++-
>  arch/arm64/include/asm/efi.h            | 19 ++++++++++++++++++-
>  drivers/firmware/efi/libstub/arm-stub.c |  7 ++++---
>  3 files changed, 35 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/include/asm/efi.h b/arch/arm/include/asm/efi.h
> index 0b06f5341b45..62620451f60b 100644
> --- a/arch/arm/include/asm/efi.h
> +++ b/arch/arm/include/asm/efi.h
> @@ -84,6 +84,18 @@ static inline void efifb_setup_from_dmi(struct screen_info *si, const char *opt)
>   */
>  #define ZIMAGE_OFFSET_LIMIT    SZ_128M
>  #define MIN_ZIMAGE_OFFSET      MAX_UNCOMP_KERNEL_SIZE
> -#define MAX_FDT_OFFSET         ZIMAGE_OFFSET_LIMIT
> +
> +/* on ARM, the FDT should be located in the first 128 MB of RAM */
> +static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
> +{
> +               return dram_base + ZIMAGE_OFFSET_LIMIT;
> +}
> +
> +/* on ARM, the initrd should be loaded in a lowmem region */
> +static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
> +                                                   unsigned long image_addr)
> +{
> +       return dram_base + SZ_512M;
> +}
>
>  #endif /* _ASM_ARM_EFI_H */
> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
> index 0b6b1633017f..6a6c8a0d1424 100644
> --- a/arch/arm64/include/asm/efi.h
> +++ b/arch/arm64/include/asm/efi.h
> @@ -46,7 +46,24 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
>   * 2MiB so we know it won't cross a 2MiB boundary.
>   */
>  #define EFI_FDT_ALIGN  SZ_2M   /* used by allocate_new_fdt_and_exit_boot() */
> -#define MAX_FDT_OFFSET SZ_512M
> +
> +/* on arm64, 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;
> +}
> +
> +/*
> + * On arm64, the initrd must be completely inside a 1 GB aligned 32 GB window
> + * that covers Image as well. Since we allocate from the top down, set a max
> + * address that is virtually guaranteed to produce a suitable allocation even
> + * when the physical address of Image is randomized.
> + */
> +static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
> +                                                   unsigned long image_addr)
> +{
> +       return ALIGN(image_addr, SZ_1G) + 31UL * SZ_1G;
> +}
>
>  #define efi_call_early(f, ...)         sys_table_arg->boottime->f(__VA_ARGS__)
>  #define __efi_call_early(f, ...)       f(__VA_ARGS__)
> diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
> index b4f7d78f9e8b..557281fe375f 100644
> --- a/drivers/firmware/efi/libstub/arm-stub.c
> +++ b/drivers/firmware/efi/libstub/arm-stub.c
> @@ -333,8 +333,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
>         if (!fdt_addr)
>                 pr_efi(sys_table, "Generating empty DTB\n");
>
> -       status = handle_cmdline_files(sys_table, image, cmdline_ptr,
> -                                     "initrd=", dram_base + SZ_512M,
> +       status = handle_cmdline_files(sys_table, image, cmdline_ptr, "initrd=",
> +                                     efi_get_max_initrd_addr(dram_base,
> +                                                             *image_addr),
>                                       (unsigned long *)&initrd_addr,
>                                       (unsigned long *)&initrd_size);
>         if (status != EFI_SUCCESS)
> @@ -344,7 +345,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
>
>         new_fdt_addr = fdt_addr;
>         status = allocate_new_fdt_and_exit_boot(sys_table, handle,
> -                               &new_fdt_addr, dram_base + MAX_FDT_OFFSET,
> +                               &new_fdt_addr, efi_get_max_fdt_addr(dram_base),
>                                 initrd_addr, initrd_size, cmdline_ptr,
>                                 fdt_addr, fdt_size);
>
> --
> 2.7.4
>