bootx_init.c:88: undefined reference to `__stack_chk_fail_local'

[Christophe LEROY]

Le 03/01/2017 à 23:50, Benjamin Herrenschmidt a écrit :
> On Tue, 2017-01-03 at 07:25 -0800, Christian Kujau wrote:
>> Hi,
>>
>> when compiling v4.10-rc2 with CONFIG_CC_STACKPROTECTOR_STRONG=y, the
>> linker fails with:
>
> The way gcc implements the stack protector has some serious
> incompatibilities with the way the Linux kernel uses r13, I wouldn't
> even try until we sort that out...

Yes indeed, it looks like recent versions of GCC don't use anymore the 
global __stack_chk_guard variable but a hard coded offset relative to r2 
or r13:

On 32 bits, it uses -7008(r2)
On 64 bits, it uses -7010(r13)

On 32 bits, r2 points to current struct, which contains the stack_canary 
value for the task. I have tried to alter get_current() in order to 
define it as an offset to r2 so that current->stack_canary is at 
-7008(r2), but I end up with circular cross references in header files 
and still have task_struct undefined when get_current() needs it to 
calculate offset of stack_canary within the structure.

When CONFIG_CC_STACKPROTECTOR is active, would it be feasible to get the 
pointer to current from the stack using the thread_info instead of using 
r2 reg ? That way we could keep r2 to point to current->stack_canary + 
0x7008

Christophe

>
> Cheers,
> Ben.
>>
>> ================================
>> + ld -EB -m elf32ppc -Bstatic --build-id -X -o .tmp_vmlinux1 -T
>> ./arch/powerpc/kernel/vmlinux.lds arch/powerpc/kernel/head_32.o
>> arch/powerpc/kernel/fpu.o arch/powerpc/kernel/vector.o
>> arch/powerpc/kernel/prom_init.o init/built-in.o --start-group
>> usr/built-in.o arch/powerpc/kernel/built-in.o arch/powerpc/mm/built-
>> in.o
>> arch/powerpc/lib/built-in.o arch/powerpc/sysdev/built-in.o
>> arch/powerpc/platforms/built-in.o arch/powerpc/math-emu/built-in.o
>> arch/powerpc/crypto/built-in.o arch/powerpc/net/built-in.o
>> kernel/built-in.o certs/built-in.o mm/built-in.o fs/built-in.o
>> ipc/built-in.o security/built-in.o crypto/built-in.o block/built-
>> in.o
>> lib/lib.a lib/built-in.o drivers/built-in.o sound/built-in.o
>> firmware/built-in.o net/built-in.o virt/built-in.o --end-group
>> arch/powerpc/platforms/built-in.o: In function `bootx_printf':
>> /usr/local/src/linux-
>> git/arch/powerpc/platforms/powermac/bootx_init.c:88: undefined
>> reference to `__stack_chk_fail_local'
>> arch/powerpc/platforms/built-in.o: In function
>> `bootx_add_display_props':
>> /usr/local/src/linux-
>> git/arch/powerpc/platforms/powermac/bootx_init.c:211: undefined
>> reference to `__stack_chk_fail_local'
>> arch/powerpc/platforms/built-in.o: In function
>> `bootx_scan_dt_build_struct':
>> /usr/local/src/linux-
>> git/arch/powerpc/platforms/powermac/bootx_init.c:350: undefined
>> reference to `__stack_chk_fail_local'
>> arch/powerpc/platforms/built-in.o: In function `bootx_init':
>> /usr/local/src/linux-
>> git/arch/powerpc/platforms/powermac/bootx_init.c:596: undefined
>> reference to `__stack_chk_fail_local'
>> /usr/bin/ld.bfd.real: .tmp_vmlinux1: hidden symbol
>> `__stack_chk_fail_local' isn't defined
>> /usr/bin/ld.bfd.real: final link failed: Bad value
>> ================================
>>
>>
>> $ ld --version | head -1
>> GNU ld (GNU Binutils for Debian) 2.25
>>
>> $ gcc --version | head -1
>> gcc-4.9.real (Debian 4.9.2-10) 4.9.2
>>
>>
>> I'm regularly compiling userspace programs with -fstack-protector
>> w/o
>> problems. I suspect it's either
>> 6533b7c16ee5712041b4e324100550e02a9a5dda
>> ("powerpc: Initial stack protector (-fstack-protector) support") or
>> 902e06eb86cd62753974c249bd1dedae2825b430 ("powerpc/32: Change the
>> stack
>> protector canary value per task") or both but I haven't started the
>> bisection yet.
>>
>> Any other ideas?
>>
>> Thanks,
>> Christian.