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

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Romain,

I was wondering if you had the chance to work on this topic ?

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@gmail.com>
> > Cc: Thomas Petazzoni <thomas.petazzoni@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



-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com