[Buildroot] [PATCH]Libssp support

[Baruch Siach]

Hi Guy,

On Thu, Jun 08, 2017 at 11:43:57AM +0000, Guy Benyei wrote:
> The code I'm trying to build is not part of the buildroot package - it's a 
> sample program I tried to compile to test the availability of the SSP 
> feature in the GCC built by buildroot (arc/nps400 target). This feature is 
> supported by GCC, pretty simple and useful, and apparently just needs the 
> related libssp to be available.
> I understand, that also uClibc can support SSP, but I'd prefer not to add 
> anything to uClibc if I don't have to. Having libssp available seems to do a 
> reasonable job for this case, without changing anything else.

Well, you are changing the toolchain, but at the gcc end instead of the libc 
one. Your suggested patch can't be accepted as is since it does not handle 
BR2_TOOLCHAIN_HAS_SSP, for example, but there is probably more to it that I'm 
not aware of. A complete solution would inevitably be more complex. I believe 
you'll need to make a more convincing case for Buildroot maintainers to accept 
this added complexity.

Why do you prefer the gcc change over the libc one?

baruch

> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> 
> unsigned int __stack_chk_guard = 0xDEADBEEF;
> 
> __attribute__((noreturn))
> void __stack_chk_fail(void)
> {
> 	printf("The canary died!\n");
> 	exit(0);
> }
> 
> __attribute__((noinline)) void foo(const char* str)
> {
> 	char buffer[16];
> 	strcpy(buffer, str);
> }
> 
> int main(int argc, char *argv[]) {
> 	if (argc!=2) {
> 		printf("Expected single command line option string to copy!\n");
> 		return -1;
> 	}
> 
> 	/* if argv[1] is at least 16 character long (17 including the trailing \0)
> 	   a buffer overrun will occur, and the __stack_chk_fail handler will be called */
> 	foo(argv[1]);
> 
> 	return -1;
> }
> 
> 
> 
> -----Original Message-----
> From: Baruch Siach [mailto:baruch at tkos.co.il] 
> Sent: Wednesday, June 7, 2017 11:13 PM
> To: Guy Benyei <guybe at mellanox.com>
> Cc: buildroot at busybox.net
> Subject: Re: [Buildroot] [PATCH]Libssp support
> 
> Hi Guy,
> 
> On Wed, Jun 07, 2017 at 10:41:51AM +0000, Guy Benyei wrote:
> > I tried to activate gcc's -fstack-protector flag, but the compiler was 
> > looking for libssp:
> > 
> > .../toolchain/bin/arceb-linux-gcc  -O2 -o stack_overrun 
> > stack_overrun.c -fstack-protector
> > .../arceb-ezchip-linux-uclibc/bin/ld: cannot find -lssp_nonshared
> > .../arceb-ezchip-linux-uclibc/bin/ld: cannot find -lssp
> > collect2: error: ld returned 1 exit status
> 
> What code are you trying to build? Is this part of a Buildroot package?
> 
> A sane build system must check whether the compiler supports -fstack-protector before attempting to use it.
> 
> > Building libssp seems to be disabled with no option to enable it in 
> > package/gcc.mk by using the --disable-libssp flag for configuring gcc.
> > Applying the patch below enables the usage of libssp. Of course, it 
> > could be conditional with some configuration symbol, to save place 
> > when libssp is not needed.
> > Any thoughts on it?
> 
> The internal toolchain that package/gcc/gcc.mk builds relies on ssp support from the C library. In your case this is seems to be uClibc. You need to enable BR2_TOOLCHAIN_BUILDROOT_USE_SSP (under "uClibc Options") for stack smashing protection support.
> 
> > It seems to be related to this bug:
> > https://bugs.busybox.net/show_bug.cgi?id=4039
> 
> This bug is about external toolchains. Unrelated to gcc.mk that only deals with the internal toolchain.
> 
> baruch
> 
> > diff --git a/package/gcc/gcc-final/gcc-final.mk 
> > b/package/gcc/gcc-final/gcc-final.mk
> > index e8d2e18..d0f23c9 100644
> > --- a/package/gcc/gcc-final/gcc-final.mk
> > +++ b/package/gcc/gcc-final/gcc-final.mk
> > @@ -147,6 +147,15 @@ endef
> >  
> >  HOST_GCC_FINAL_POST_INSTALL_HOOKS += HOST_GCC_FINAL_INSTALL_LIBATOMIC
> >  
> > +define HOST_GCC_FINAL_INSTALL_LIBSSP
> > +       -cp -dpf $(HOST_GCC_FINAL_GCC_LIB_DIR)/libssp* \
> > +               $(STAGING_DIR)/lib/
> > +       -cp -dpf $(HOST_GCC_FINAL_GCC_LIB_DIR)/libssp* \
> > +               $(TARGET_DIR)/lib/
> > +endef
> > +
> > +HOST_GCC_FINAL_POST_INSTALL_HOOKS += HOST_GCC_FINAL_INSTALL_LIBSSP
> > +
> >  # Handle the installation of libraries in /usr/lib  
> > HOST_GCC_FINAL_USR_LIBS =
> >  
> > diff --git a/package/gcc/gcc.mk b/package/gcc/gcc.mk index 
> > b52f945..cca3847 100644
> > --- a/package/gcc/gcc.mk
> > +++ b/package/gcc/gcc.mk
> > @@ -90,7 +90,6 @@ HOST_GCC_COMMON_CONF_OPTS = \
> >         --with-sysroot=$(STAGING_DIR) \
> >         --disable-__cxa_atexit \
> >         --with-gnu-ld \
> > -       --disable-libssp \
> >         --disable-multilib \
> >         --with-gmp=$(HOST_DIR)/usr \
> >         --with-mpc=$(HOST_DIR)/usr \

-- 
     http://baruch.siach.name/blog/                  ~. .~   Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch at tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -