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

[Ard Biesheuvel]

On 9 February 2017 at 17:06, Jeffrey Hugo <jhugo at codeaurora.org> wrote:
> 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.
>

The 32 GB does not have to be 32 GB aligned, only 1 GB aligned. So as
long as the follow expression holds, we should be fine


align(max(kernel_end, initrd_end), 1g) - align_down (min
(kernel_start, initrd_start), 1g) <= 32g


> 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.