s390: clean .bss before running uncompressed kernel

Clean uncompressed kernel .bss section in the startup code before
the uncompressed kernel is executed. At this point of time initrd and
certificates have been already rescued. Uncompressed kernel .bss size
is known from vmlinux_info. It is also taken into consideration during
uncompressed kernel positioning by kaslr (so it is safe to clean it).

With that uncompressed kernel is starting with .bss section zeroed and
no .bss section usage restrictions apply. Which makes chkbss checks for
uncompressed kernel objects obsolete and they can be removed.

early_nobss.c is also not needed anymore. Parts of it which are still
relevant are moved to early.c. Kasan initialization code is now called
directly from head64 (early.c is instrumented and should not be
executed before kasan shadow memory is set up).

Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/boot/startup.c

@@ -112,6 +112,11 @@ static void handle_relocs(unsigned long offset)
 	}
 }
 
+static void clear_bss_section(void)
+{
+	memset((void *)vmlinux.default_lma + vmlinux.image_size, 0, vmlinux.bss_size);
+}
+
 void startup_kernel(void)
 {
 	unsigned long random_lma;
@@ -151,6 +156,7 @@ void startup_kernel(void)
 	} else if (__kaslr_offset)
 		memcpy((void *)vmlinux.default_lma, img, vmlinux.image_size);
 
+	clear_bss_section();
 	copy_bootdata();
 	if (IS_ENABLED(CONFIG_RELOCATABLE))
 		handle_relocs(__kaslr_offset);

arch/s390/kernel/Makefile

@@ -10,20 +10,12 @@ CFLAGS_REMOVE_ftrace.o		= $(CC_FLAGS_FTRACE)
 
 # Do not trace early setup code
 CFLAGS_REMOVE_early.o		= $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_early_nobss.o	= $(CC_FLAGS_FTRACE)
 
 endif
 
 GCOV_PROFILE_early.o		:= n
-GCOV_PROFILE_early_nobss.o	:= n
-
 KCOV_INSTRUMENT_early.o		:= n
-KCOV_INSTRUMENT_early_nobss.o	:= n
-
 UBSAN_SANITIZE_early.o		:= n
-UBSAN_SANITIZE_early_nobss.o	:= n
-
-KASAN_SANITIZE_early_nobss.o	:= n
 KASAN_SANITIZE_ipl.o		:= n
 KASAN_SANITIZE_machine_kexec.o	:= n
 
@@ -48,7 +40,7 @@ CFLAGS_ptrace.o		+= -DUTS_MACHINE='"$(UTS_MACHINE)"'
 
 obj-y	:= traps.o time.o process.o base.o early.o setup.o idle.o vtime.o
 obj-y	+= processor.o sys_s390.o ptrace.o signal.o cpcmd.o ebcdic.o nmi.o
-obj-y	+= debug.o irq.o ipl.o dis.o diag.o vdso.o early_nobss.o
+obj-y	+= debug.o irq.o ipl.o dis.o diag.o vdso.o
 obj-y	+= sysinfo.o lgr.o os_info.o machine_kexec.o pgm_check.o
 obj-y	+= runtime_instr.o cache.o fpu.o dumpstack.o guarded_storage.o sthyi.o
 obj-y	+= entry.o reipl.o relocate_kernel.o kdebugfs.o alternative.o
@@ -90,6 +82,3 @@ obj-$(CONFIG_TRACEPOINTS)	+= trace.o
 # vdso
 obj-y				+= vdso64/
 obj-$(CONFIG_COMPAT_VDSO)	+= vdso32/
-
-chkbss := head64.o early_nobss.o
-include $(srctree)/arch/s390/scripts/Makefile.chkbss

arch/s390/kernel/early.c

@@ -32,6 +32,21 @@
 #include <asm/boot_data.h>
 #include "entry.h"
 
+static void __init reset_tod_clock(void)
+{
+	u64 time;
+
+	if (store_tod_clock(&time) == 0)
+		return;
+	/* TOD clock not running. Set the clock to Unix Epoch. */
+	if (set_tod_clock(TOD_UNIX_EPOCH) != 0 || store_tod_clock(&time) != 0)
+		disabled_wait();
+
+	memset(tod_clock_base, 0, 16);
+	*(__u64 *) &tod_clock_base[1] = TOD_UNIX_EPOCH;
+	S390_lowcore.last_update_clock = TOD_UNIX_EPOCH;
+}
+
 /*
  * Initialize storage key for kernel pages
  */
@@ -301,6 +316,7 @@ static void __init check_image_bootable(void)
 
 void __init startup_init(void)
 {
+	reset_tod_clock();
 	check_image_bootable();
 	time_early_init();
 	init_kernel_storage_key();

arch/s390/kernel/head64.S

@@ -34,11 +34,9 @@ ENTRY(startup_continue)
 	larl	%r14,init_task
 	stg	%r14,__LC_CURRENT
 	larl	%r15,init_thread_union+THREAD_SIZE-STACK_FRAME_OVERHEAD
-#
-# Early setup functions that may not rely on an initialized bss section,
-# like moving the initrd. Returns with an initialized bss section.
-#
-	brasl	%r14,startup_init_nobss
+#ifdef CONFIG_KASAN
+	brasl	%r14,kasan_early_init
+#endif
 #
 # Early machine initialization and detection functions.
 #

arch/s390/lib/Makefile

@@ -11,6 +11,3 @@ lib-$(CONFIG_UPROBES) += probes.o
 # Instrumenting memory accesses to __user data (in different address space)
 # produce false positives
 KASAN_SANITIZE_uaccess.o := n
-
-chkbss := mem.o
-include $(srctree)/arch/s390/scripts/Makefile.chkbss

drivers/s390/char/Makefile

@@ -49,6 +49,3 @@ obj-$(CONFIG_CRASH_DUMP) += sclp_sdias.o zcore.o
 
 hmcdrv-objs := hmcdrv_mod.o hmcdrv_dev.o hmcdrv_ftp.o hmcdrv_cache.o diag_ftp.o sclp_ftp.o
 obj-$(CONFIG_HMC_DRV) += hmcdrv.o
-
-chkbss := sclp_early_core.o
-include $(srctree)/arch/s390/scripts/Makefile.chkbss