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:

6533b7c1 ("powerpc: Initial stack protector (-fstack-protector) support")
902e06eb ("powerpc/32: Change the stack protector canary value per task")

Fixes: 6533b7c1 ("powerpc: Initial stack protector (-fstack-protector) support")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig

@@ -164,7 +164,6 @@ config PPC
 	select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE
 	select HAVE_ARCH_HARDENED_USERCOPY
 	select HAVE_KERNEL_GZIP
-	select HAVE_CC_STACKPROTECTOR
 
 config GENERIC_CSUM
 	def_bool CPU_LITTLE_ENDIAN

arch/powerpc/include/asm/stackprotector.h

-/*
- * GCC stack protector support.
- *
- * Stack protector works by putting predefined pattern at the start of
- * the stack frame and verifying that it hasn't been overwritten when
- * returning from the function.  The pattern is called stack canary
- * and gcc expects it to be defined by a global variable called
- * "__stack_chk_guard" on PPC.  This unfortunately means that on SMP
- * we cannot have a different canary value per task.
- */
-
-#ifndef _ASM_STACKPROTECTOR_H
-#define _ASM_STACKPROTECTOR_H
-
-#include <linux/random.h>
-#include <linux/version.h>
-#include <asm/reg.h>
-
-extern unsigned long __stack_chk_guard;
-
-/*
- * Initialize the stackprotector canary value.
- *
- * NOTE: this must only be called from functions that never return,
- * and it must always be inlined.
- */
-static __always_inline void boot_init_stack_canary(void)
-{
-	unsigned long canary;
-
-	/* Try to get a semi random initial value. */
-	get_random_bytes(&canary, sizeof(canary));
-	canary ^= mftb();
-	canary ^= LINUX_VERSION_CODE;
-
-	current->stack_canary = canary;
-	__stack_chk_guard = current->stack_canary;
-}
-
-#endif	/* _ASM_STACKPROTECTOR_H */

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)