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

Ard Biesheuvel
2017-02-10T06:38:11Z

> On 10 Feb 2017, at 00:42, Ruigrok, Richard <rruigrok-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> wrote:
>
>
>
>> 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
>

No. The efi stub is built into the kernel, so there we can be lax about these things. For boot loaders, 32GB remains a reasonable limit because some configurations require it

>> #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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