Re: [PATCH v2] BaseTools/GCC AARCH64: force disable PIC code generation

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 31 March 2017 at 09:59, Laszlo Ersek <lersek@redhat.com> wrote:
> On 03/31/17 10:40, Ard Biesheuvel wrote:
>> As a security measure, some distro toolchains now default to PIC code
>> generation, allowing executables (as opposed to shared libraries) using
>> the objects to be built as PIE binaries, which can be loaded at a random
>> virtual offset.
>>
>> However, our ELF to PE/COFF generation code does not deal with the
>> resulting relocation types (i.e., GOT based), and so the use of PIC code
>> leads to GenFw errors.
>>
>> Given that
>> a) our non-PIC PE/COFF executables are already relocatable,
>> b) PIC code leads to all symbol references to be indirected via GOT
>>    entries containing absolute addresses, each requiring an entry in the
>>    relocation table,
>> c) the AArch64 ISA makes it perfectly feasible to built PIE executables
>>    from non-PIC code,
>>
>> there is absolutely no upside to using PIC code for building EDK2 modules,
>> and so we're better off simply disabling it unconditionally.
>>
>> Note that when running under the OS, the GOT has an additional advantage,
>> i.e., that all .text/.rodata pages remain clean and so can be shared between
>> processes. This does not apply to the UEFI environment, however.
>>
>> Contributed-under: TianoCore Contribution Agreement 1.0
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  BaseTools/Conf/tools_def.template | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
>> index 0aabdeb2d973..2c5cd5808912 100755
>> --- a/BaseTools/Conf/tools_def.template
>> +++ b/BaseTools/Conf/tools_def.template
>> @@ -4341,7 +4341,7 @@ DEFINE GCC_X64_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mno-red-zone -Wno-ad
>>  DEFINE GCC_IPF_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -minline-int-divide-min-latency
>>  DEFINE GCC_ARM_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -mabi=aapcs -fno-short-enums -funsigned-char -ffunction-sections -fdata-sections -fomit-frame-pointer -fno-builtin -Wno-address -mthumb -mfloat-abi=soft
>>  DEFINE GCC_ARM_CC_XIPFLAGS         = -mno-unaligned-access
>> -DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm -funsigned-char  -ffunction-sections -fdata-sections -fno-builtin -Wno-address -fno-asynchronous-unwind-tables
>> +DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm -funsigned-char  -ffunction-sections -fdata-sections -fno-builtin -Wno-address -fno-asynchronous-unwind-tables -fno-pic
>>  DEFINE GCC_AARCH64_CC_XIPFLAGS     = -mstrict-align
>>  DEFINE GCC_DLINK_FLAGS_COMMON      = -nostdlib --pie
>>  DEFINE GCC_DLINK2_FLAGS_COMMON     = -Wl,--script=$(EDK_TOOLS_PATH)/Scripts/GccBase.lds
>>
>
> Sounds convincing enough to me. I find it quite annoying that such an
> important property of code generation (-fpic or -fno-pic by default)
> varies across distros. Well, security.
>
> Acked-by: Laszlo Ersek <lersek@redhat.com>
>

Thanks, pushed as c2d56a894b32