[Buildroot] [PATCH] SSP: disable ssp support on microblaze

Sat Sep 8 13:17:07 UTC 2018

Hi Thomas,

Le 07/09/2018 à 09:26, Thomas Petazzoni a écrit :
> Romain,
> 
> I was wondering if you had the chance to work on this topic ?

Thanks for the reminder.

I'll take a look.

Best regards,
Romain

> 
> Thanks,
> 
> Thomas
> 
> On Sun, 1 Jul 2018 14:55:22 +0200, Thomas Petazzoni wrote:
>> Hello,
>>
>> On Sun, 10 Jun 2018 18:33:00 +0200, Romain Naour wrote:
>>> As reported by [1], SSP support is missing in the Buildroot toolchain
>>> for microblaze even if it's requested by selecting
>>> BR2_TOOLCHAIN_HAS_SSP config option.
>>>
>>> In Buildroot, we are using libssp provided by the C library (Glibc,
>>> musl, uClibc-ng) when available. We are not using libssp from gcc.
>>>
>>> So for a microblaze glibc based toolchain, the SSP support is enabled
>>> unconditionally by a select BR2_TOOLCHAIN_HAS_SSP.
>>>
>>> BR2_microblazeel=y
>>> BR2_TOOLCHAIN_BUILDROOT_GLIBC=y
>>> BR2_KERNEL_HEADERS_4_14=y
>>> BR2_BINUTILS_VERSION_2_30_X=y
>>> BR2_GCC_VERSION_8_X=y
>>> BR2_TOOLCHAIN_BUILDROOT_CXX=y
>>>
>>> While building the toolchain, we are building host-binutils which
>>> provide "as" (assembler) and host-gcc-initial wich provide a
>>> minimal cross gcc (C only cross-compiler without any C library).
>>> When SSP support is requested, gcc_cv_libc_provides_ssp=yes is
>>> added to the make command line (see [2] for full details)
>>>
>>> With this setting, the SSP support is requested but it's not available
>>> in the end and the toochain build succeed.
>>>
>>> When the microblaze toolchain is imported to Biuldroot (2018.05) as
>>> external toolchain with BR2_TOOLCHAIN_EXTERNAL_HAS_SSP set, the build
>>> stop with :
>>> "SSP support not available in this toolchain, please disable BR2_TOOLCHAIN_EXTERNAL_HAS_SSP"
>>>
>>> The test is doing the following command line:
>>>
>>> echo 'void main(){}' | [...]/host/bin/microblazeel-linux-gcc.br_real -Werror -fstack-protector -x c - -o [...]/build/.br-toolchain-test.tmp
>>> cc1: error: -fstack-protector not supported for this target [-Werror]
>>>
>>> When we look at the gcc-final log file (config.log) we can see this
>>> error several time when using the minimal gcc (from host-gcc-initial).
>>> So Why the minimal gcc doesn't support SSP?
>>>
>>> When we look at the gcc-initial log file (config.log) we can see an
>>> error with 'as':
>>>
>>> configure:23194: checking assembler for cfi directives
>>> configure:23209: [...]microblazeel-buildroot-linux-gnu/bin/as    -o conftest.o conftest.s >&5
>>> conftest.s: Assembler messages:
>>> conftest.s:2: Error: CFI is not supported for this target
>>> conftest.s:3: Error: CFI is not supported for this target
>>> conftest.s:4: Error: CFI is not supported for this target
>>> conftest.s:5: Error: CFI is not supported for this target
>>> conftest.s:6: Error: CFI is not supported for this target
>>> conftest.s:7: Error: CFI is not supported for this target
>>> configure:23212: $? = 1
>>> configure: failed program was
>>>     .text
>>>     .cfi_startproc
>>>     .cfi_offset 0, 0
>>>     .cfi_same_value 1
>>>     .cfi_def_cfa 1, 2
>>>     .cfi_escape 1, 2, 3, 4, 5
>>>     .cfi_endproc
>>>
>>> This is the only relevant difference compared to a nios2 toolchain where
>>> libssp is enabled and available (nios2 is an example).
>>>
>>> "CFI" stand for "Control Flow Integrity" and it seems that SSP support
>>> requires CFI target support (see [3] for some explanation).
>>>
>>> The SSP support seems to depends on CFI support, but the toolchain
>>> infrastructure is not detailed enough to handle the CFI dependency.
>>>
>>> In the other hand, microblaze is the only architecture where CFI support
>>> is missing.
>>>
>>> Disable SSP support for microblaze entirely.
>>>
>>> Fixes:
>>> https://gitlab.com/free-electrons/toolchains-builder/-/jobs/72006389
>>>
>>> [1] https://gitlab.com/free-electrons/toolchains-builder/issues/1
>>> [2] https://git.buildroot.net/buildroot/tree/package/gcc/gcc.mk?h=2018.05#n275
>>> [3] https://grsecurity.net/rap_faq.php
>>>
>>> Signed-off-by: Romain Naour <romain.naour at gmail.com>
>>> Cc: Thomas Petazzoni <thomas.petazzoni at bootlin.com>  
>>
>> Thanks for working on this. Based on this explanation, I think I'd
>> prefer to see something like this in package/binutils/Config.in.host
>>
>> config BR2_PACKAGE_HOST_BINUTILS_SUPPORTS_CFI
>> 	default y
>> 	depends on !BR2_microblaze
>>
>>> diff --git a/package/glibc/Config.in b/package/glibc/Config.in
>>> index 57a2e833d2..7adf76699d 100644
>>> --- a/package/glibc/Config.in
>>> +++ b/package/glibc/Config.in
>>> @@ -4,6 +4,7 @@ config BR2_PACKAGE_GLIBC
>>>  	bool
>>>  	default y
>>>  	select BR2_PACKAGE_LINUX_HEADERS
>>> -	select BR2_TOOLCHAIN_HAS_SSP
>>> +	# SSP not supported on microblaze
>>> +	select BR2_TOOLCHAIN_HAS_SSP if !BR2_microblaze  
>>
>> 	select BR2_TOOLCHAIN_HAS_SSP if BR2_PACKAGE_HOST_BINUTILS_SUPPORTS_CFI
>>
>>> diff --git a/package/musl/Config.in b/package/musl/Config.in
>>> index bedc50cd45..4e0d6f4ef1 100644
>>> --- a/package/musl/Config.in
>>> +++ b/package/musl/Config.in
>>> @@ -4,6 +4,7 @@ config BR2_PACKAGE_MUSL
>>>  	depends on BR2_TOOLCHAIN_USES_MUSL
>>>  	select BR2_PACKAGE_LINUX_HEADERS
>>>  	# SSP broken on i386/ppc: http://www.openwall.com/lists/musl/2016/12/04/2
>>> -	select BR2_TOOLCHAIN_HAS_SSP if !(BR2_i386 || BR2_powerpc)
>>> +	# SSP not supported on microblaze
>>> +	select BR2_TOOLCHAIN_HAS_SSP if !(BR2_i386 || BR2_microblaze || BR2_powerpc)  
>>
>> 	select BR2_TOOLCHAIN_HAS_SSP if BR2_PACKAGE_HOST_BINUTILS_SUPPORTS_CFI && !(BR2_i386 || BR2_powerpc)
>>
>>>  config BR2_TOOLCHAIN_BUILDROOT_USE_SSP
>>>  	bool "Enable stack protection support"
>>> +	depends on !BR2_microblaze # SSP not supported on microblaze  
>>
>> 	depends on BR2_PACKAGE_HOST_BINUTILS_SUPPORTS_CFI
>>
>>>  	select BR2_TOOLCHAIN_HAS_SSP
>>>  	help
>>>  	  Enable stack smashing protection support using GCCs
>>> diff --git a/toolchain/Config.in b/toolchain/Config.in
>>> index 3a53a32a6d..1bf71a6d52 100644
>>> --- a/toolchain/Config.in
>>> +++ b/toolchain/Config.in
>>> @@ -122,6 +122,9 @@ config BR2_TOOLCHAIN_HAS_THREADS_NPTL
>>>  
>>>  config BR2_TOOLCHAIN_HAS_SSP
>>>  	bool
>>> +	# SSP support require CFI architecture support.
>>> +	# https://gitlab.com/free-electrons/toolchains-builder/issues/1
>>> +	depends on !BR2_microblaze # missing CFI support in "gas"  
>>
>> And this change is not necessary. Really BR2_TOOLCHAIN_HAS_SSP
>> is a blind option that indicates if the toolchain has SSP support or
>> not, it's not meant to handle the dependencies of SSP. support.
>>
>> Could you rework your patch accordingly if you agree with the proposal ?
>>
>> Thanks!
>>
>> Thomas
> 
> 
> 