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.
