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

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

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 (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com