powerpc: Revert the initial stack protector support

Unfortunately the stack protector support we merged recently only works
on some toolchains. If the toolchain is built without glibc support
everything works fine, but if glibc is built then it leads to a panic
at boot.

The solution is not rc5 material, so revert the support for now. This
reverts commits:

6533b7c16e ("powerpc: Initial stack protector (-fstack-protector) support")
902e06eb86 ("powerpc/32: Change the stack protector canary value per task")

Fixes: 6533b7c16e ("powerpc: Initial stack protector (-fstack-protector) support")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/Makefile

@@ -19,10 +19,6 @@ CFLAGS_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
 
-# -fstack-protector triggers protection checks in this code,
-# but it is being used too early to link to meaningful stack_chk logic.
-CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
-
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
 CFLAGS_REMOVE_cputable.o = -mno-sched-epilog $(CC_FLAGS_FTRACE)

arch/powerpc/kernel/asm-offsets.c

@@ -91,9 +91,6 @@ int main(void)
 	DEFINE(TI_livepatch_sp, offsetof(struct thread_info, livepatch_sp));
 #endif
 
-#ifdef CONFIG_CC_STACKPROTECTOR
-	DEFINE(TSK_STACK_CANARY, offsetof(struct task_struct, stack_canary));
-#endif
 	DEFINE(KSP, offsetof(struct thread_struct, ksp));
 	DEFINE(PT_REGS, offsetof(struct thread_struct, regs));
 #ifdef CONFIG_BOOKE

arch/powerpc/kernel/entry_32.S

@@ -674,11 +674,7 @@ BEGIN_FTR_SECTION
 	mtspr	SPRN_SPEFSCR,r0		/* restore SPEFSCR reg */
 END_FTR_SECTION_IFSET(CPU_FTR_SPE)
 #endif /* CONFIG_SPE */
-#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
-	lwz	r0,TSK_STACK_CANARY(r2)
-	lis	r4,__stack_chk_guard@ha
-	stw	r0,__stack_chk_guard@l(r4)
-#endif
+
 	lwz	r0,_CCR(r1)
 	mtcrf	0xFF,r0
 	/* r3-r12 are destroyed -- Cort */

arch/powerpc/kernel/process.c

@@ -64,12 +64,6 @@
 #include <linux/kprobes.h>
 #include <linux/kdebug.h>
 
-#ifdef CONFIG_CC_STACKPROTECTOR
-#include <linux/stackprotector.h>
-unsigned long __stack_chk_guard __read_mostly;
-EXPORT_SYMBOL(__stack_chk_guard);
-#endif
-
 /* Transactional Memory debug */
 #ifdef TM_DEBUG_SW
 #define TM_DEBUG(x...) printk(KERN_INFO x)