[PATCH AUTOSEL 6.1 20/35] s390: workaround invalid gcc-11 out of bounds read warning

[Sasha Levin <sashal@kernel.org>]

From: Heiko Carstens <hca@linux.ibm.com>

[ Upstream commit 41e1992665a2701fa025a8b76970c43b4148446f ]

GCC 11.1.0 and 11.2.0 generate a wrong warning when compiling the
kernel e.g. with allmodconfig:

arch/s390/kernel/setup.c: In function ‘setup_lowcore_dat_on’:
./include/linux/fortify-string.h:57:33: error: ‘__builtin_memcpy’ reading 128 bytes from a region of size 0 [-Werror=stringop-overread]
...
arch/s390/kernel/setup.c:526:9: note: in expansion of macro ‘memcpy’
  526 |         memcpy(abs_lc->cregs_save_area, S390_lowcore.cregs_save_area,
      |         ^~~~~~

This could be addressed by using absolute_pointer() with the
S390_lowcore macro, but this is not a good idea since this generates
worse code for performance critical paths.

Therefore simply use a for loop to copy the array in question and get
rid of the warning.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/s390/kernel/setup.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index ab19ddb09d65..2ec5f1e0312f 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -507,6 +507,7 @@ static void __init setup_lowcore_dat_on(void)
 {
 	struct lowcore *abs_lc;
 	unsigned long flags;
+	int i;
 
 	__ctl_clear_bit(0, 28);
 	S390_lowcore.external_new_psw.mask |= PSW_MASK_DAT;
@@ -521,8 +522,8 @@ static void __init setup_lowcore_dat_on(void)
 	abs_lc = get_abs_lowcore(&flags);
 	abs_lc->restart_flags = RESTART_FLAG_CTLREGS;
 	abs_lc->program_new_psw = S390_lowcore.program_new_psw;
-	memcpy(abs_lc->cregs_save_area, S390_lowcore.cregs_save_area,
-	       sizeof(abs_lc->cregs_save_area));
+	for (i = 0; i < 16; i++)
+		abs_lc->cregs_save_area[i] = S390_lowcore.cregs_save_area[i];
 	put_abs_lowcore(abs_lc, flags);
 }
 
-- 
2.39.0