From: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Subject: s390/noexec: execute kexec datamover without DAT
Patch-mainline: v4.15-rc1
Git-commit: d0e810eeb3d326978f248b8f0233a2f30f58c72d
References: bnc#1066799, LTC#161403
Description: s390/noexec: execute kexec datamover without DAT
Symptom: System hangs when using kexec on new hardware with no-execute
support (z14).
Problem: The datamover code gets executed with DAT on (MMU is active)
and the page that contains the datamover is marked as non-
executable. Therefore when branching into the datamover an
unexpected program check happens and afterwards the machine
is dead.
Solution: Disable DAT, which also disables any no-execute checks, just
before the datamover gets executed.
Reproduction: Use kexec on new hardware with no-execute support (z14).
Upstream-Description:
s390/noexec: execute kexec datamover without DAT
Rebooting into a new kernel with kexec fails (system dies) if tried on
a machine that has no-execute support. Reason for this is that the so
called datamover code gets executed with DAT on (MMU is active) and
the page that contains the datamover is marked as non-executable.
Therefore when branching into the datamover an unexpected program
check happens and afterwards the machine is dead.
This can be simply avoided by disabling DAT, which also disables any
no-execute checks, just before the datamover gets executed.
In fact the first thing done by the datamover is to disable DAT. The
code in the datamover that disables DAT can be removed as well.
Thanks to Michael Holzheu and Gerald Schaefer for tracking this down.
Reviewed-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.vnet.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Fixes: 57d7f939e7bd ("s390: add no-execute support")
Cc: <stable@vger.kernel.org> # v4.11+
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Acked-by: Hannes Reinecke <hare@suse.com>
---
arch/s390/kernel/machine_kexec.c | 1 +
arch/s390/kernel/relocate_kernel.S | 3 ---
2 files changed, 1 insertion(+), 3 deletions(-)
--- a/arch/s390/kernel/machine_kexec.c
+++ b/arch/s390/kernel/machine_kexec.c
@@ -268,6 +268,7 @@ static void __do_machine_kexec(void *dat
s390_reset_system();
data_mover = (relocate_kernel_t) page_to_phys(image->control_code_page);
+ __arch_local_irq_stnsm(0xfb); /* disable DAT - avoid no-execute */
/* Call the moving routine */
(*data_mover)(&image->head, image->start);
--- a/arch/s390/kernel/relocate_kernel.S
+++ b/arch/s390/kernel/relocate_kernel.S
@@ -27,7 +27,6 @@
ENTRY(relocate_kernel)
basr %r13,0 # base address
.base:
- stnsm sys_msk-.base(%r13),0xfb # disable DAT
stctg %c0,%c15,ctlregs-.base(%r13)
stmg %r0,%r15,gprregs-.base(%r13)
lghi %r0,3
@@ -101,8 +100,6 @@ ENTRY(relocate_kernel)
.align 8
load_psw:
.long 0x00080000,0x80000000
- sys_msk:
- .quad 0
ctlregs:
.rept 16
.quad 0