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

Sat Sep 8 14:02:08 UTC 2018

Le 01/07/2018 à 14:55, Thomas Petazzoni a écrit :
> 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

The CFI support also depends on binutils version.

For example, NiosII gained CFI support with binutils 2.30.
The nios2--glibc--bleeding-edge-2017.05-toolchains-1-2.tar.bz2 toolchain is
affected by this issue. You can't import it with Buildroot > 2018.02.

Best regards,
Romain

> 
>> 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
> 