[ 45/75] s390: critical section cleanup vs. machine checks

Greg Kroah-Hartman
2013-03-18T21:56:31Z

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

commit 6551fbdfd8b85d1ab5822ac98abb4fb449bcfae0 upstream.

The current machine check code uses the registers stored by the machine
in the lowcore at __LC_GPREGS_SAVE_AREA as the registers of the interrupted
context. The registers 0-7 of a user process can get clobbered if a machine
checks interrupts the execution of a critical section in entry[64].S.

The reason is that the critical section cleanup code may need to modify
the PSW and the registers for the previous context to get to the end of a
critical section. If registers 0-7 have to be replaced the relevant copy
will be in the registers, which invalidates the copy in the lowcore. The
machine check handler needs to explicitly store registers 0-7 to the stack.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/kernel/entry.S | 3 ++-
arch/s390/kernel/entry64.S | 5 +++--
2 files changed, 5 insertions(+), 3 deletions(-)

--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -636,7 +636,8 @@ ENTRY(mcck_int_handler)
UPDATE_VTIME %r14,%r15,__LC_MCCK_ENTER_TIMER
mcck_skip:
SWITCH_ASYNC __LC_GPREGS_SAVE_AREA+32,__LC_PANIC_STACK,PAGE_SHIFT
- mvc __PT_R0(64,%r11),__LC_GPREGS_SAVE_AREA
+ stm %r0,%r7,__PT_R0(%r11)
+ mvc __PT_R8(32,%r11),__LC_GPREGS_SAVE_AREA+32
stm %r8,%r9,__PT_PSW(%r11)
xc __SF_BACKCHAIN(4,%r15),__SF_BACKCHAIN(%r15)
l %r1,BASED(.Ldo_machine_check)
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -678,8 +678,9 @@ ENTRY(mcck_int_handler)
UPDATE_VTIME %r14,__LC_MCCK_ENTER_TIMER
LAST_BREAK %r14
mcck_skip:
- lghi %r14,__LC_GPREGS_SAVE_AREA
- mvc __PT_R0(128,%r11),0(%r14)
+ lghi %r14,__LC_GPREGS_SAVE_AREA+64
+ stmg %r0,%r7,__PT_R0(%r11)
+ mvc __PT_R8(64,%r11),0(%r14)
stmg %r8,%r9,__PT_PSW(%r11)
xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
lgr %r2,%r11 # pass pointer to pt_regs