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

[Jeffrey Hugo]

On 2/9/2017 3:16 AM, 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 currently a theoretical scenario,
> since it only affects systems where the size of RAM exceeds the size of
> the linear mapping.)
>
> 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>
> ---

I'll give this a test on our platform that was running into the current 
limitation - probably this weekend.

I reviewed the code and its ok, but I do have one question.  Do we need 
to handle the case where initrd ends up below the kernel?

Lets assume KALSR puts the kernel somewhere up high in DDR, after the 
32GB mark in DDR.  Now lets assume the unlikely scenario that the initrd 
won't fit anywhere after 32GB, but will fit before 32GB.  Per my 
understanding of efi_high_alloc, it will put the initrd before the 32GB 
mark, which will be outside of the window where the kernel is.

Seems like there are 3 options -
1. We consider the scenario unlikely to the point that we don't care, 
and don't do anything
2. We check to see if initrd is allocated to be within the window, and 
if not print an error message
3. Change efi_high_alloc to take a min addess as well as a max, so that 
it will fail if the initrd can't fit in the window (which will result in 
an error message printed)

Thoughts?

>  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);
>
>


-- 
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm 
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.