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>

3 files changed, 83 insertions, 44 deletions

diff --git a/arch/s390/include/asm/switch_to.h b/arch/s390/include/asm/switch_to.h
index 6dbd559763c9..29c81f82705e 100644
--- a/arch/s390/include/asm/switch_to.h
+++ b/arch/s390/include/asm/switch_to.h
@@ -13,58 +13,94 @@
 extern struct task_struct *__switch_to(void *, void *);
 extern void update_cr_regs(struct task_struct *task);
 
-static inline void save_fp_regs(s390_fp_regs *fpregs)
+static inline int test_fp_ctl(u32 fpc)
 {
+	u32 orig_fpc;
+	int rc;
+
+	if (!MACHINE_HAS_IEEE)
+		return 0;
+
 	asm volatile(
-		"	std	0,%O0+8(%R0)\n"
-		"	std	2,%O0+24(%R0)\n"
-		"	std	4,%O0+40(%R0)\n"
-		"	std	6,%O0+56(%R0)"
-		: "=Q" (*fpregs) : "Q" (*fpregs));
+		"	efpc    %1\n"
+		"	sfpc	%2\n"
+		"0:	sfpc	%1\n"
+		"	la	%0,0\n"
+		"1:\n"
+		EX_TABLE(0b,1b)
+		: "=d" (rc), "=d" (orig_fpc)
+		: "d" (fpc), "0" (-EINVAL));
+	return rc;
+}
+
+static inline void save_fp_ctl(u32 *fpc)
+{
 	if (!MACHINE_HAS_IEEE)
 		return;
+
 	asm volatile(
-		"	stfpc	%0\n"
-		"	std	1,%O0+16(%R0)\n"
-		"	std	3,%O0+32(%R0)\n"
-		"	std	5,%O0+48(%R0)\n"
-		"	std	7,%O0+64(%R0)\n"
-		"	std	8,%O0+72(%R0)\n"
-		"	std	9,%O0+80(%R0)\n"
-		"	std	10,%O0+88(%R0)\n"
-		"	std	11,%O0+96(%R0)\n"
-		"	std	12,%O0+104(%R0)\n"
-		"	std	13,%O0+112(%R0)\n"
-		"	std	14,%O0+120(%R0)\n"
-		"	std	15,%O0+128(%R0)\n"
-		: "=Q" (*fpregs) : "Q" (*fpregs));
+		"       stfpc   %0\n"
+		: "+Q" (*fpc));
 }
 
-static inline void restore_fp_regs(s390_fp_regs *fpregs)
+static inline int restore_fp_ctl(u32 *fpc)
 {
+	int rc;
+
+	if (!MACHINE_HAS_IEEE)
+		return 0;
+
 	asm volatile(
-		"	ld	0,%O0+8(%R0)\n"
-		"	ld	2,%O0+24(%R0)\n"
-		"	ld	4,%O0+40(%R0)\n"
-		"	ld	6,%O0+56(%R0)"
-		: : "Q" (*fpregs));
+		"0:	lfpc    %1\n"
+		"	la	%0,0\n"
+		"1:\n"
+		EX_TABLE(0b,1b)
+		: "=d" (rc) : "Q" (*fpc), "0" (-EINVAL));
+	return rc;
+}
+
+static inline void save_fp_regs(freg_t *fprs)
+{
+	asm volatile("std 0,%0" : "=Q" (fprs[0]));
+	asm volatile("std 2,%0" : "=Q" (fprs[2]));
+	asm volatile("std 4,%0" : "=Q" (fprs[4]));
+	asm volatile("std 6,%0" : "=Q" (fprs[6]));
 	if (!MACHINE_HAS_IEEE)
 		return;
-	asm volatile(
-		"	lfpc	%0\n"
-		"	ld	1,%O0+16(%R0)\n"
-		"	ld	3,%O0+32(%R0)\n"
-		"	ld	5,%O0+48(%R0)\n"
-		"	ld	7,%O0+64(%R0)\n"
-		"	ld	8,%O0+72(%R0)\n"
-		"	ld	9,%O0+80(%R0)\n"
-		"	ld	10,%O0+88(%R0)\n"
-		"	ld	11,%O0+96(%R0)\n"
-		"	ld	12,%O0+104(%R0)\n"
-		"	ld	13,%O0+112(%R0)\n"
-		"	ld	14,%O0+120(%R0)\n"
-		"	ld	15,%O0+128(%R0)\n"
-		: : "Q" (*fpregs));
+	asm volatile("std 1,%0" : "=Q" (fprs[1]));
+	asm volatile("std 3,%0" : "=Q" (fprs[3]));
+	asm volatile("std 5,%0" : "=Q" (fprs[5]));
+	asm volatile("std 7,%0" : "=Q" (fprs[7]));
+	asm volatile("std 8,%0" : "=Q" (fprs[8]));
+	asm volatile("std 9,%0" : "=Q" (fprs[9]));
+	asm volatile("std 10,%0" : "=Q" (fprs[10]));
+	asm volatile("std 11,%0" : "=Q" (fprs[11]));
+	asm volatile("std 12,%0" : "=Q" (fprs[12]));
+	asm volatile("std 13,%0" : "=Q" (fprs[13]));
+	asm volatile("std 14,%0" : "=Q" (fprs[14]));
+	asm volatile("std 15,%0" : "=Q" (fprs[15]));
+}
+
+static inline void restore_fp_regs(freg_t *fprs)
+{
+	asm volatile("ld 0,%0" : : "Q" (fprs[0]));
+	asm volatile("ld 2,%0" : : "Q" (fprs[2]));
+	asm volatile("ld 4,%0" : : "Q" (fprs[4]));
+	asm volatile("ld 6,%0" : : "Q" (fprs[6]));
+	if (!MACHINE_HAS_IEEE)
+		return;
+	asm volatile("ld 1,%0" : : "Q" (fprs[1]));
+	asm volatile("ld 3,%0" : : "Q" (fprs[3]));
+	asm volatile("ld 5,%0" : : "Q" (fprs[5]));
+	asm volatile("ld 7,%0" : : "Q" (fprs[7]));
+	asm volatile("ld 8,%0" : : "Q" (fprs[8]));
+	asm volatile("ld 9,%0" : : "Q" (fprs[9]));
+	asm volatile("ld 10,%0" : : "Q" (fprs[10]));
+	asm volatile("ld 11,%0" : : "Q" (fprs[11]));
+	asm volatile("ld 12,%0" : : "Q" (fprs[12]));
+	asm volatile("ld 13,%0" : : "Q" (fprs[13]));
+	asm volatile("ld 14,%0" : : "Q" (fprs[14]));
+	asm volatile("ld 15,%0" : : "Q" (fprs[15]));
 }
 
 static inline void save_access_regs(unsigned int *acrs)
@@ -83,12 +119,14 @@ static inline void restore_access_regs(unsigned int *acrs)
 
 #define switch_to(prev,next,last) do {					\
 	if (prev->mm) {							\
-		save_fp_regs(&prev->thread.fp_regs);			\
+		save_fp_ctl(&prev->thread.fp_regs.fpc);			\
+		save_fp_regs(prev->thread.fp_regs.fprs);		\
 		save_access_regs(&prev->thread.acrs[0]);		\
 		save_ri_cb(prev->thread.ri_cb);				\
 	}								\
 	if (next->mm) {							\
-		restore_fp_regs(&next->thread.fp_regs);			\
+		restore_fp_ctl(&next->thread.fp_regs.fpc);		\
+		restore_fp_regs(next->thread.fp_regs.fprs);		\
 		restore_access_regs(&next->thread.acrs[0]);		\
 		restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb);	\
 		update_cr_regs(next);					\
diff --git a/arch/s390/include/uapi/asm/ptrace.h b/arch/s390/include/uapi/asm/ptrace.h
index 7a84619e315e..1d2f47548e1d 100644
--- a/arch/s390/include/uapi/asm/ptrace.h
+++ b/arch/s390/include/uapi/asm/ptrace.h
@@ -199,6 +199,7 @@ typedef union
 typedef struct
 {
 	__u32   fpc;
+	__u32	pad;
 	freg_t  fprs[NUM_FPRS];              
 } s390_fp_regs;
 
@@ -206,7 +207,6 @@ typedef struct
 #define FPC_FLAGS_MASK          0x00F80000
 #define FPC_DXC_MASK            0x0000FF00
 #define FPC_RM_MASK             0x00000003
-#define FPC_VALID_MASK          0xF8F8FF03
 
 /* this typedef defines how a Program Status Word looks like */
 typedef struct 
diff --git a/arch/s390/include/uapi/asm/sigcontext.h b/arch/s390/include/uapi/asm/sigcontext.h
index 584787f6ce44..b30de9c01bbe 100644
--- a/arch/s390/include/uapi/asm/sigcontext.h
+++ b/arch/s390/include/uapi/asm/sigcontext.h
@@ -49,6 +49,7 @@ typedef struct
 typedef struct
 {
 	unsigned int fpc;
+	unsigned int pad;
 	double   fprs[__NUM_FPRS];
 } _s390_fp_regs;