Re: [PATCH 6/7] efi: restrict arm/arm64 linux loader initrd placement

[Daniel Kiper]

On Mon, Jun 12, 2017 at 03:53:40PM +0100, Leif Lindholm wrote:
> The 32-bit arm Linux kernel is built as a zImage, which self-decompresses
> down to near start of RAM. In order for an initrd/initramfs to be
> accessible, it needs to be placed within the first ~768MB of RAM.
> The initrd loader built into the kernel EFI stub restricts this down to
> 512MB for simplicity - so enable the same restriction in grub.
>
> For arm64, the requirement is within a 1GB aligned 32GB window also
> covering the (runtime) kernel image. Since the EFI stub loader itself
> will attempt to relocate to near start of RAM, force initrd to be loaded
> completely within the first 32GB of RAM.
>
> Signed-off-by: Leif Lindholm <address@hidden>
> ---
>  grub-core/loader/arm64/linux.c | 39 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/grub-core/loader/arm64/linux.c b/grub-core/loader/arm64/linux.c
> index 8cd44230d..7e989c2b9 100644
> --- a/grub-core/loader/arm64/linux.c
> +++ b/grub-core/loader/arm64/linux.c
> @@ -35,6 +35,23 @@
>
>  GRUB_MOD_LICENSE ("GPLv3+");
>
> +/*
> + * As per linux/Documentation/arm/Booting
> + * ARM initrd needs to be covered by kernel linear mapping,
> + * so place it in the first 512MB of DRAM.
> + *
> + * As per linux/Documentation/arm64/booting.txt
> + * ARM64 initrd needs to be contained entirely within a 1GB aligned window
> + * of up to 32GB of size that covers the kernel image as well.
> + * Since the EFI stub loader will attempt to load the kernel near start of
> + * RAM, place the buffer in the first 32GB of RAM.
> + */
> +#ifdef __arm__
> +#define INITRD_MAX_ADDRESS_OFFSET (512U * 1024 * 1024)
> +#else /* __aarch64__ */
> +#define INITRD_MAX_ADDRESS_OFFSET (32ULL * 1024 * 1024 * 1024)
> +#endif
> +
>  static grub_dl_t my_mod;
>  static int loaded;
>
> @@ -194,6 +211,25 @@ grub_linux_unload (void)
>    return GRUB_ERR_NONE;
>  }
>
> +/*
> + * This function returns a pointer to a legally allocated initrd buffer,
> + * or NULL if unsuccessful
> + */
> +static void *
> +allocate_initrd_mem (int initrd_pages)
> +{
> +  grub_addr_t max_addr;
> +
> +  if (grub_efi_get_dram_base (&max_addr) != GRUB_ERR_NONE)
> +    return NULL;
> +
> +  max_addr += INITRD_MAX_ADDRESS_OFFSET - 1;

I do not understand this. Why do not pass simply INITRD_MAX_ADDRESS_OFFSET
instead of max_addr to grub_efi_allocate_pages_real()?

> +  return grub_efi_allocate_pages_real (max_addr, initrd_pages,
> +                                    GRUB_EFI_ALLOCATE_MAX_ADDRESS,
> +                                    GRUB_EFI_LOADER_DATA);
> +}

Daniel