s390: use init_thread_union aka initial stack for the first process

s390 is the only architecture which switches from the initial stack to a
later on allocated different stack for the first process.
This is (at least) problematic for the stackleak feature, which instruments
functions to save the current stackpointer within the task structure of the
running process.

The stackleak code compares stack pointers of the current process - and
doesn't expect that the kernel stack of a task can change. Even though the
stackleak feature itself will not cause any harm, the assumption about
kernel stacks being consistent is there, and only s390 doesn't follow that.

Therefore switch back to use init_thread_union, just like all other
architectures.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

2 files changed, 19 insertions, 31 deletions

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 061cc771d764..76cfc7c23e70 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -380,6 +380,12 @@ void stack_free(unsigned long stack)
 #endif
 }
 
+void __init arch_call_rest_init(void)
+{
+	smp_reinit_ipl_cpu();
+	rest_init();
+}
+
 int __init arch_early_irq_init(void)
 {
 	unsigned long stack;
@@ -391,28 +397,21 @@ int __init arch_early_irq_init(void)
 	return 0;
 }
 
-void __init arch_call_rest_init(void)
+static unsigned long __init stack_alloc_early(void)
 {
 	unsigned long stack;
 
-	smp_reinit_ipl_cpu();
-	stack = stack_alloc();
-	if (!stack)
-		panic("Couldn't allocate kernel stack");
-	current->stack = (void *) stack;
-#ifdef CONFIG_VMAP_STACK
-	current->stack_vm_area = (void *) stack;
-#endif
-	set_task_stack_end_magic(current);
-	stack += STACK_INIT_OFFSET;
-	S390_lowcore.kernel_stack = stack;
-	call_on_stack_noreturn(rest_init, stack);
+	stack = (unsigned long)memblock_alloc(THREAD_SIZE, THREAD_SIZE);
+	if (!stack) {
+		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
+		      __func__, THREAD_SIZE, THREAD_SIZE);
+	}
+	return stack;
 }
 
 static void __init setup_lowcore(void)
 {
 	struct lowcore *lc, *abs_lc;
-	unsigned long mcck_stack;
 
 	/*
 	 * Setup lowcore for boot cpu
@@ -436,7 +435,6 @@ static void __init setup_lowcore(void)
 	lc->io_new_psw.mask = PSW_KERNEL_BITS | PSW_MASK_MCHECK;
 	lc->io_new_psw.addr = (unsigned long) io_int_handler;
 	lc->clock_comparator = clock_comparator_max;
-	lc->nodat_stack = ((unsigned long)&init_thread_union) + STACK_INIT_OFFSET;
 	lc->current_task = (unsigned long)&init_task;
 	lc->lpp = LPP_MAGIC;
 	lc->machine_flags = S390_lowcore.machine_flags;
@@ -449,17 +447,14 @@ static void __init setup_lowcore(void)
 	lc->steal_timer = S390_lowcore.steal_timer;
 	lc->last_update_timer = S390_lowcore.last_update_timer;
 	lc->last_update_clock = S390_lowcore.last_update_clock;
-
 	/*
 	 * Allocate the global restart stack which is the same for
-	 * all CPUs in cast *one* of them does a PSW restart.
+	 * all CPUs in case *one* of them does a PSW restart.
 	 */
-	restart_stack = memblock_alloc(THREAD_SIZE, THREAD_SIZE);
-	if (!restart_stack)
-		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
-		      __func__, THREAD_SIZE, THREAD_SIZE);
-	restart_stack += STACK_INIT_OFFSET;
-
+	restart_stack = (void *)(stack_alloc_early() + STACK_INIT_OFFSET);
+	lc->mcck_stack = stack_alloc_early() + STACK_INIT_OFFSET;
+	lc->nodat_stack = stack_alloc_early() + STACK_INIT_OFFSET;
+	lc->kernel_stack = S390_lowcore.kernel_stack;
 	/*
 	 * Set up PSW restart to call ipl.c:do_restart(). Copy the relevant
 	 * restart data to the absolute zero lowcore. This is necessary if
@@ -470,13 +465,6 @@ static void __init setup_lowcore(void)
 	lc->restart_data = 0;
 	lc->restart_source = -1U;
 	__ctl_store(lc->cregs_save_area, 0, 15);
-
-	mcck_stack = (unsigned long)memblock_alloc(THREAD_SIZE, THREAD_SIZE);
-	if (!mcck_stack)
-		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
-		      __func__, THREAD_SIZE, THREAD_SIZE);
-	lc->mcck_stack = mcck_stack + STACK_INIT_OFFSET;
-
 	lc->spinlock_lockval = arch_spin_lockval(0);
 	lc->spinlock_index = 0;
 	arch_spin_lock_setup(0);
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 680b4fbdabb1..cc98ac26e77c 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -1295,7 +1295,7 @@ int __init smp_reinit_ipl_cpu(void)
 
 	free_pages(lc_ipl->async_stack - STACK_INIT_OFFSET, THREAD_SIZE_ORDER);
 	memblock_free_late(__pa(lc_ipl->mcck_stack - STACK_INIT_OFFSET), THREAD_SIZE);
+	memblock_free_late(__pa(lc_ipl->nodat_stack - STACK_INIT_OFFSET), THREAD_SIZE);
 	memblock_free_late(__pa(lc_ipl), sizeof(*lc_ipl));
-
 	return 0;
 }