Re: [PATCH v2 1/2] efi: arm-stub: Correct FDT and initrd allocation rules for arm64

["Ruigrok, Richard" <rruigrok-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 2/9/2017 2:42 PM, Ard Biesheuvel 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 mostly a theoretical scenario, since
> it only affects systems where the physical memory footprint exceeds the
> size of the linear mapping.)
>
> Since we know the kernel itself will be covered by the linear mapping,
> choose a suitably sized window (i.e., based on the size of the linear
> region) covering the kernel when allocating memory for the initrd.
>
> 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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  arch/arm/include/asm/efi.h              | 14 +++++++++++++-
>  arch/arm64/include/asm/efi.h            | 18 +++++++++++++++++-
>  drivers/firmware/efi/libstub/arm-stub.c |  7 ++++---
>  3 files changed, 34 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/include/asm/efi.h b/arch/arm/include/asm/efi.h
> index 0b06f5341b45..2de0195dfd1e 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..342e90d6d204 100644
> --- a/arch/arm64/include/asm/efi.h
> +++ b/arch/arm64/include/asm/efi.h
> @@ -46,7 +46,23 @@ 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, we have to ensure that the initrd ends up in the linear region,
> + * which is a 1 GB aligned region of size '1UL << (VA_BITS - 1)' that is
> + * guaranteed to cover the kernel Image.
> + */
> +static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
> +						    unsigned long image_addr)
> +{
> +	return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS - 1));
> +}
>  
Please update booting.txt which specifies a window of 32G for ARM64

>  #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);
>  

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