[U-Boot] [PATCH v0 21/20] efi_loader: hack for archs that cannot do unaligned accesses

Sat Aug 5 16:52:59 UTC 2017

On 08/05/2017 06:16 PM, Rob Clark wrote:
> On Sat, Aug 5, 2017 at 12:12 PM, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>> On 08/05/2017 05:58 PM, Rob Clark wrote:
>>> Some arch's have trouble with unaligned accesses.  Technically
>>> EFI device-path structs should be byte aligned, and the next node
>>> in the path starts immediately after the previous.  Meaning that
>>> a pointer to an 'struct efi_device_path' is not necessarily word
>>> aligned.  See section 10.3.1 in v2.7 of UEFI spec.
>>>
>>> This causes problems not just for u-boot, but also most/all EFI
>>> payloads loaded by u-boot on these archs.  Fortunately the common
>>> practice for traversing a device path is to rely on the length
>>> field in the header, rather than the specified length of the
>>> particular device path type+subtype.  So the EFI_DP_PAD() macro
>>> will add the specified number of bytes to the tail of device path
>>> structs to pad them to word alignment.
>>>
>>> Technically this is non-compliant, BROKEN_UNALIGNED should *only*
>>> be defined on archs that cannot do unaligned accesses.
>>>
>>> Signed-off-by: Rob Clark <robdclark at gmail.com>
>>> ---
>>> I'm not sure if there are other arch's that need -DBROKEN_UNALIGNED
>>>
>>> Mark, this is untested but I think it should solve your crash on the
>>> Banana Pi.  Could you give it a try when you get a chance?
>>>
>>>  arch/arm/config.mk               |  2 +-
>>>  include/efi_api.h                | 30 ++++++++++++++++++++++++++++++
>>>  lib/efi_loader/efi_device_path.c |  3 +++
>>>  3 files changed, 34 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm/config.mk b/arch/arm/config.mk
>>> index 1a77779db4..067dc93a9d 100644
>>> --- a/arch/arm/config.mk
>>> +++ b/arch/arm/config.mk
>>> @@ -28,7 +28,7 @@ LLVMS_RELFLAGS              := $(call cc-option,-mllvm,) \
>>>                       $(call cc-option,-arm-use-movt=0,)
>>>  PLATFORM_RELFLAGS    += $(LLVM_RELFLAGS)
>>>
>>> -PLATFORM_CPPFLAGS += -D__ARM__
>>> +PLATFORM_CPPFLAGS += -D__ARM__ -DBROKEN_UNALIGNED
>>
>> NAK
>>
>> We have more then ARM. And other architectures also create exceptions
>> for unaligned access.
>>
>> I hate platform specific code. It should not be used outside /arch.
>>
>> To play it save you should not use _packed at all!
>> Use memcpy to transfer between aligned and unaligned memory.
> 
> except for reasons I explained in the thread on the patch that added
> the __packed in the first place.  Sorry, this is ugly but we have to
> do it.
> 
> BR,
> -R

According to the UEFI standard the nodes in paths are not to be assumed
to be aligned.

So even if you use padding bytes in paths that you pass to the EFI
application you should not expect that the EFI application does the
same. Expect the EFI application either to remove them or send new nodes
without padding.

To the idea of padding bytes and __packed does not make sense.

Best regards

Heinrich

> 
> 
>> Best regards
>>
>> Heinrich
>>
>>>
>>>  ifdef CONFIG_ARM64
>>>  PLATFORM_ELFFLAGS += -B aarch64 -O elf64-littleaarch64
>>> diff --git a/include/efi_api.h b/include/efi_api.h
>>> index ef91e34c7b..ddd1e6100a 100644
>>> --- a/include/efi_api.h
>>> +++ b/include/efi_api.h
>>> @@ -284,6 +284,31 @@ struct efi_loaded_image {
>>>  #define DEVICE_PATH_TYPE_END                 0x7f
>>>  #  define DEVICE_PATH_SUB_TYPE_END           0xff
>>>
>>> +/*
>>> + * Some arch's have trouble with unaligned accesses.  Technically
>>> + * EFI device-path structs should be byte aligned, and the next node
>>> + * in the path starts immediately after the previous.  Meaning that
>>> + * a pointer to an 'struct efi_device_path' is not necessarily word
>>> + * aligned.  See section 10.3.1 in v2.7 of UEFI spec.
>>> + *
>>> + * This causes problems not just for u-boot, but also most/all EFI
>>> + * payloads loaded by u-boot on these archs.  Fortunately the common
>>> + * practice for traversing a device path is to rely on the length
>>> + * field in the header, rather than the specified length of the
>>> + * particular device path type+subtype.  So the EFI_DP_PAD() macro
>>> + * will add the specified number of bytes to the tail of device path
>>> + * structs to pad them to word alignment.
>>> + *
>>> + * Technically this is non-compliant, BROKEN_UNALIGNED should *only*
>>> + * be defined on archs that cannot do unaligned accesses.
>>> + */
>>> +
>>> +#ifdef BROKEN_UNALIGNED
>>> +#  define EFI_DP_PAD(n)  u8 __pad[n]
>>> +#else
>>> +#  define EFI_DP_PAD(n)
>>> +#endif
>>> +
>>>  struct efi_device_path {
>>>       u8 type;
>>>       u8 sub_type;
>>> @@ -318,12 +343,14 @@ struct efi_device_path_usb {
>>>       struct efi_device_path dp;
>>>       u8 parent_port_number;
>>>       u8 usb_interface;
>>> +     EFI_DP_PAD(2);
>>>  } __packed;
>>>
>>>  struct efi_device_path_mac_addr {
>>>       struct efi_device_path dp;
>>>       struct efi_mac_addr mac;
>>>       u8 if_type;
>>> +     EFI_DP_PAD(3);
>>>  } __packed;
>>>
>>>  struct efi_device_path_usb_class {
>>> @@ -333,11 +360,13 @@ struct efi_device_path_usb_class {
>>>       u8 device_class;
>>>       u8 device_subclass;
>>>       u8 device_protocol;
>>> +     EFI_DP_PAD(1);
>>>  } __packed;
>>>
>>>  struct efi_device_path_sd_mmc_path {
>>>       struct efi_device_path dp;
>>>       u8 slot_number;
>>> +     EFI_DP_PAD(3);
>>>  } __packed;
>>>
>>>  #define DEVICE_PATH_TYPE_MEDIA_DEVICE                0x04
>>> @@ -353,6 +382,7 @@ struct efi_device_path_hard_drive_path {
>>>       u8 partition_signature[16];
>>>       u8 partmap_type;
>>>       u8 signature_type;
>>> +     EFI_DP_PAD(1);
>>>  } __packed;
>>>
>>>  struct efi_device_path_cdrom_path {
>>> diff --git a/lib/efi_loader/efi_device_path.c b/lib/efi_loader/efi_device_path.c
>>> index b5acf73f98..515a1f4737 100644
>>> --- a/lib/efi_loader/efi_device_path.c
>>> +++ b/lib/efi_loader/efi_device_path.c
>>> @@ -402,6 +402,9 @@ struct efi_device_path *efi_dp_from_file(struct blk_desc *desc, int part,
>>>
>>>       // TODO efi_device_path_file_path should be variable length:
>>>       fpsize = sizeof(struct efi_device_path) + 2 * (strlen(path) + 1);
>>> +#ifdef BROKEN_UNALIGNED
>>> +     fpsize = ALIGN(fpsize, 4);
>>> +#endif
>>>       dpsize += fpsize;
>>>
>>>       start = buf = calloc(1, dpsize + sizeof(END));
>>>
>>
> 