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>

7 files changed, 26 insertions, 68 deletions

diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 7b0d05414618..596ca7cc4d7b 100644
--- a/arch/s390/boot/startup.c
+++ b/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);
diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index 0f255b54b051..7edbbcd8228a 100644
--- a/arch/s390/kernel/Makefile
+++ b/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
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 6312fed48530..b432d63d0b37 100644
--- a/arch/s390/kernel/early.c
+++ b/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();
diff --git a/arch/s390/kernel/early_nobss.c b/arch/s390/kernel/early_nobss.c
deleted file mode 100644
index 52a3ef959341..000000000000
--- a/arch/s390/kernel/early_nobss.c
+++ /dev/null
@@ -1,45 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- *    Copyright IBM Corp. 2007, 2018
- */
-
-/*
- * Early setup functions which may not rely on an initialized bss
- * section. The last thing that is supposed to happen here is
- * initialization of the bss section.
- */
-
-#include <linux/processor.h>
-#include <linux/string.h>
-#include <asm/sections.h>
-#include <asm/lowcore.h>
-#include <asm/timex.h>
-#include <asm/kasan.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;
-}
-
-static void __init clear_bss_section(void)
-{
-	memset(__bss_start, 0, __bss_stop - __bss_start);
-}
-
-void __init startup_init_nobss(void)
-{
-	reset_tod_clock();
-	clear_bss_section();
-	kasan_early_init();
-}
diff --git a/arch/s390/kernel/head64.S b/arch/s390/kernel/head64.S
index 5aea1a527443..143ed71221fe 100644
--- a/arch/s390/kernel/head64.S
+++ b/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.
 #
diff --git a/arch/s390/lib/Makefile b/arch/s390/lib/Makefile
index a1ec63abfb95..d7c218e8b559 100644
--- a/arch/s390/lib/Makefile
+++ b/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 $(srctree)/arch/s390/scripts/Makefile.chkbss
diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
index b8a8816d94e7..845e12ac5954 100644
--- a/drivers/s390/char/Makefile
+++ b/drivers/s390/char/Makefile
@@ -49,6 +49,3 @@ obj-$(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