[PATCH 6.18 177/309] s390/entry: Scrub r12 register on kernel entry

Greg Kroah-Hartman
2026-03-31T17:04:14Z

From: Vasily Gorbik <gor@linux.ibm.com>

commit 0738d395aab8fae3b5a3ad3fc640630c91693c27 upstream.

Before commit f33f2d4c7c80 ("s390/bp: remove TIF_ISOLATE_BP"),
all entry handlers loaded r12 with the current task pointer
(lg %r12,__LC_CURRENT) for use by the BPENTER/BPEXIT macros. That
commit removed TIF_ISOLATE_BP, dropping both the branch prediction
macros and the r12 load, but did not add r12 to the register clearing
sequence.

Add the missing xgr %r12,%r12 to make the register scrub consistent
across all entry points.

Fixes: f33f2d4c7c80 ("s390/bp: remove TIF_ISOLATE_BP")
Cc: stable@kernel.org
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/s390/kernel/entry.S | 3 +++
1 file changed, 3 insertions(+)

--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -254,6 +254,7 @@ SYM_CODE_START(system_call)
xgr %r9,%r9
xgr %r10,%r10
xgr %r11,%r11
+ xgr %r12,%r12
la %r2,STACK_FRAME_OVERHEAD(%r15) # pointer to pt_regs
mvc __PT_R8(64,%r2),__LC_SAVE_AREA(%r13)
MBEAR %r2,%r13
@@ -390,6 +391,7 @@ SYM_CODE_START(\name)
xgr %r6,%r6
xgr %r7,%r7
xgr %r10,%r10
+ xgr %r12,%r12
xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
mvc __PT_R8(64,%r11),__LC_SAVE_AREA(%r13)
MBEAR %r11,%r13
@@ -479,6 +481,7 @@ SYM_CODE_START(mcck_int_handler)
xgr %r6,%r6
xgr %r7,%r7
xgr %r10,%r10
+ xgr %r12,%r12
stmg %r8,%r9,__PT_PSW(%r11)
xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)