s390: fix save and restore of the floating-point-control register

The FPC_VALID_MASK has been used to check the validity of the value
to be loaded into the floating-point-control register. With the
introduction of the floating-point extension facility and the
decimal-floating-point additional bits have been defined which need
to be checked in a non straight forward way. So far these bits have
been ignored which can cause an incorrect results for decimal-
floating-point operations, e.g. an incorrect rounding mode to be
set after signal return.

The static check with the FPC_VALID_MASK is replaced with a trial
load of the floating-point-control value, see test_fp_ctl.

In addition an information leak with the padding word between the
floating-point-control word and the floating-point registers in
the s390_fp_regs is fixed.

Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index e1cdd31acabb..7ed0d4e2a435 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -165,7 +165,8 @@ int copy_thread(unsigned long clone_flags, unsigned long new_stackp,
          * save fprs to current->thread.fp_regs to merge them with
          * the emulated registers and then copy the result to the child.
          */
-        save_fp_regs(&current->thread.fp_regs);
+        save_fp_ctl(&current->thread.fp_regs.fpc);
+        save_fp_regs(current->thread.fp_regs.fprs);
         memcpy(&p->thread.fp_regs, &current->thread.fp_regs,
                sizeof(s390_fp_regs));
         /* Set a new TLS ?  */
@@ -173,7 +174,9 @@ int copy_thread(unsigned long clone_flags, unsigned long new_stackp,
                 p->thread.acrs[0] = frame->childregs.gprs[6];
 #else /* CONFIG_64BIT */
         /* Save the fpu registers to new thread structure. */
-        save_fp_regs(&p->thread.fp_regs);
+        save_fp_ctl(&p->thread.fp_regs.fpc);
+        save_fp_regs(p->thread.fp_regs.fprs);
+        p->thread.fp_regs.pad = 0;
         /* Set a new TLS ?  */
         if (clone_flags & CLONE_SETTLS) {
                 unsigned long tls = frame->childregs.gprs[6];
@@ -205,10 +208,12 @@ int dump_fpu (struct pt_regs * regs, s390_fp_regs *fpregs)
          * save fprs to current->thread.fp_regs to merge them with
          * the emulated registers and then copy the result to the dump.
          */
-        save_fp_regs(&current->thread.fp_regs);
+        save_fp_ctl(&current->thread.fp_regs.fpc);
+        save_fp_regs(current->thread.fp_regs.fprs);
         memcpy(fpregs, &current->thread.fp_regs, sizeof(s390_fp_regs));
 #else /* CONFIG_64BIT */
-        save_fp_regs(fpregs);
+        save_fp_ctl(&fpregs->fpc);
+        save_fp_regs(fpregs->fprs);
 #endif /* CONFIG_64BIT */
         return 1;
 }