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>

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);					\

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 

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;
 

arch/s390/kernel/compat_linux.h

@@ -27,6 +27,7 @@ typedef union
 typedef struct
 {
 	unsigned int	fpc;
+	unsigned int	pad;
 	freg_t32	fprs[__NUM_FPRS];              
 } _s390_fp_regs32;
 

arch/s390/kernel/compat_signal.c

@@ -153,60 +153,61 @@ int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
 
 static int save_sigregs32(struct pt_regs *regs, _sigregs32 __user *sregs)
 {
-	_s390_regs_common32 regs32;
-	int err, i;
+	_sigregs32 user_sregs;
+	int i;
 
-	regs32.psw.mask = psw32_user_bits |
+	user_sregs.regs.psw.mask = psw32_user_bits |
 		((__u32)(regs->psw.mask >> 32) & PSW32_MASK_USER);
-	regs32.psw.addr = (__u32) regs->psw.addr |
+	user_sregs.regs.psw.addr = (__u32) regs->psw.addr |
 		(__u32)(regs->psw.mask & PSW_MASK_BA);
 	for (i = 0; i < NUM_GPRS; i++)
-		regs32.gprs[i] = (__u32) regs->gprs[i];
+		user_sregs.regs.gprs[i] = (__u32) regs->gprs[i];
 	save_access_regs(current->thread.acrs);
-	memcpy(regs32.acrs, current->thread.acrs, sizeof(regs32.acrs));
-	err = __copy_to_user(&sregs->regs, &regs32, sizeof(regs32));
-	if (err)
-		return -EFAULT;
-	save_fp_regs(&current->thread.fp_regs);
-	/* s390_fp_regs and _s390_fp_regs32 are the same ! */
-	err = __copy_to_user(&sregs->fpregs, &current->thread.fp_regs,
-			     sizeof(_s390_fp_regs32));
-	if (err)
+	memcpy(&user_sregs.regs.acrs, current->thread.acrs,
+	       sizeof(user_sregs.regs.acrs));
+	save_fp_ctl(&current->thread.fp_regs.fpc);
+	save_fp_regs(current->thread.fp_regs.fprs);
+	memcpy(&user_sregs.fpregs, &current->thread.fp_regs,
+	       sizeof(user_sregs.fpregs));
+	if (__copy_to_user(sregs, &user_sregs, sizeof(_sigregs32)))
 		return -EFAULT;
 	return 0;
 }
 
 static int restore_sigregs32(struct pt_regs *regs,_sigregs32 __user *sregs)
 {
-	_s390_regs_common32 regs32;
-	int err, i;
+	_sigregs32 user_sregs;
+	int i;
 
 	/* Alwys make any pending restarted system call return -EINTR */
 	current_thread_info()->restart_block.fn = do_no_restart_syscall;
 
-	err = __copy_from_user(&regs32, &sregs->regs, sizeof(regs32));
-	if (err)
+	if (__copy_from_user(&user_sregs, &sregs->regs, sizeof(user_sregs)))
 		return -EFAULT;
+
+	/* Loading the floating-point-control word can fail. Do that first. */
+	if (restore_fp_ctl(&user_sregs.fpregs.fpc))
+		return -EINVAL;
+
+	/* Use regs->psw.mask instead of PSW_USER_BITS to preserve PER bit. */
 	regs->psw.mask = (regs->psw.mask & ~PSW_MASK_USER) |
-		(__u64)(regs32.psw.mask & PSW32_MASK_USER) << 32 |
-		(__u64)(regs32.psw.addr & PSW32_ADDR_AMODE);
+		(__u64)(user_sregs.regs.psw.mask & PSW32_MASK_USER) << 32 |
+		(__u64)(user_sregs.regs.psw.addr & PSW32_ADDR_AMODE);
 	/* Check for invalid user address space control. */
 	if ((regs->psw.mask & PSW_MASK_ASC) == PSW_ASC_HOME)
 		regs->psw.mask = PSW_ASC_PRIMARY |
 			(regs->psw.mask & ~PSW_MASK_ASC);
-	regs->psw.addr = (__u64)(regs32.psw.addr & PSW32_ADDR_INSN);
+	regs->psw.addr = (__u64)(user_sregs.regs.psw.addr & PSW32_ADDR_INSN);
 	for (i = 0; i < NUM_GPRS; i++)
-		regs->gprs[i] = (__u64) regs32.gprs[i];
-	memcpy(current->thread.acrs, regs32.acrs, sizeof(current->thread.acrs));
+		regs->gprs[i] = (__u64) user_sregs.regs.gprs[i];
+	memcpy(&current->thread.acrs, &user_sregs.regs.acrs,
+	       sizeof(current->thread.acrs));
 	restore_access_regs(current->thread.acrs);
 
-	err = __copy_from_user(&current->thread.fp_regs, &sregs->fpregs,
-			       sizeof(_s390_fp_regs32));
-	current->thread.fp_regs.fpc &= FPC_VALID_MASK;
-	if (err)
-		return -EFAULT;
+	memcpy(&current->thread.fp_regs, &user_sregs.fpregs,
+	       sizeof(current->thread.fp_regs));
 
-	restore_fp_regs(&current->thread.fp_regs);
+	restore_fp_regs(current->thread.fp_regs.fprs);
 	clear_thread_flag(TIF_SYSCALL);	/* No longer in a system call */
 	return 0;
 }

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;
 }

arch/s390/kernel/ptrace.c

@@ -239,8 +239,7 @@ static unsigned long __peek_user(struct task_struct *child, addr_t addr)
 		offset = addr - (addr_t) &dummy->regs.fp_regs;
 		tmp = *(addr_t *)((addr_t) &child->thread.fp_regs + offset);
 		if (addr == (addr_t) &dummy->regs.fp_regs.fpc)
-			tmp &= (unsigned long) FPC_VALID_MASK
-				<< (BITS_PER_LONG - 32);
+			tmp <<= BITS_PER_LONG - 32;
 
 	} else if (addr < (addr_t) (&dummy->regs.per_info + 1)) {
 		/*
@@ -363,10 +362,10 @@ static int __poke_user(struct task_struct *child, addr_t addr, addr_t data)
 		/*
 		 * floating point regs. are stored in the thread structure
 		 */
-		if (addr == (addr_t) &dummy->regs.fp_regs.fpc &&
-		    (data & ~((unsigned long) FPC_VALID_MASK
-			      << (BITS_PER_LONG - 32))) != 0)
-			return -EINVAL;
+		if (addr == (addr_t) &dummy->regs.fp_regs.fpc)
+			if ((unsigned int) data != 0 ||
+			    test_fp_ctl(data >> (BITS_PER_LONG - 32)))
+				return -EINVAL;
 		offset = addr - (addr_t) &dummy->regs.fp_regs;
 		*(addr_t *)((addr_t) &child->thread.fp_regs + offset) = data;
 
@@ -696,8 +695,7 @@ static int __poke_user_compat(struct task_struct *child,
 		 * floating point regs. are stored in the thread structure 
 		 */
 		if (addr == (addr_t) &dummy32->regs.fp_regs.fpc &&
-		    (tmp & ~FPC_VALID_MASK) != 0)
-			/* Invalid floating point control. */
+		    test_fp_ctl(tmp))
 			return -EINVAL;
 	        offset = addr - (addr_t) &dummy32->regs.fp_regs;
 		*(__u32 *)((addr_t) &child->thread.fp_regs + offset) = tmp;
@@ -895,8 +893,10 @@ static int s390_fpregs_get(struct task_struct *target,
 			   const struct user_regset *regset, unsigned int pos,
 			   unsigned int count, void *kbuf, void __user *ubuf)
 {
-	if (target == current)
-		save_fp_regs(&target->thread.fp_regs);
+	if (target == current) {
+		save_fp_ctl(&target->thread.fp_regs.fpc);
+		save_fp_regs(target->thread.fp_regs.fprs);
+	}
 
 	return user_regset_copyout(&pos, &count, &kbuf, &ubuf,
 				   &target->thread.fp_regs, 0, -1);
@@ -909,19 +909,21 @@ static int s390_fpregs_set(struct task_struct *target,
 {
 	int rc = 0;
 
-	if (target == current)
-		save_fp_regs(&target->thread.fp_regs);
+	if (target == current) {
+		save_fp_ctl(&target->thread.fp_regs.fpc);
+		save_fp_regs(target->thread.fp_regs.fprs);
+	}
 
 	/* If setting FPC, must validate it first. */
 	if (count > 0 && pos < offsetof(s390_fp_regs, fprs)) {
-		u32 fpc[2] = { target->thread.fp_regs.fpc, 0 };
-		rc = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &fpc,
+		u32 ufpc[2] = { target->thread.fp_regs.fpc, 0 };
+		rc = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &ufpc,
 					0, offsetof(s390_fp_regs, fprs));
 		if (rc)
 			return rc;
-		if ((fpc[0] & ~FPC_VALID_MASK) != 0 || fpc[1] != 0)
+		if (ufpc[1] != 0 || test_fp_ctl(ufpc[0]))
 			return -EINVAL;
-		target->thread.fp_regs.fpc = fpc[0];
+		target->thread.fp_regs.fpc = ufpc[0];
 	}
 
 	if (rc == 0 && count > 0)
@@ -929,8 +931,10 @@ static int s390_fpregs_set(struct task_struct *target,
 					target->thread.fp_regs.fprs,
 					offsetof(s390_fp_regs, fprs), -1);
 
-	if (rc == 0 && target == current)
-		restore_fp_regs(&target->thread.fp_regs);
+	if (rc == 0 && target == current) {
+		restore_fp_ctl(&target->thread.fp_regs.fpc);
+		restore_fp_regs(target->thread.fp_regs.fprs);
+	}
 
 	return rc;
 }

arch/s390/kernel/signal.c

@@ -62,14 +62,15 @@ static int save_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
 	user_sregs.regs.psw.addr = regs->psw.addr;
 	memcpy(&user_sregs.regs.gprs, &regs->gprs, sizeof(sregs->regs.gprs));
 	memcpy(&user_sregs.regs.acrs, current->thread.acrs,
-	       sizeof(sregs->regs.acrs));
+	       sizeof(user_sregs.regs.acrs));
 	/* 
 	 * We have to store the fp registers to current->thread.fp_regs
 	 * to merge them with the emulated registers.
 	 */
-	save_fp_regs(&current->thread.fp_regs);
+	save_fp_ctl(&current->thread.fp_regs.fpc);
+	save_fp_regs(current->thread.fp_regs.fprs);
 	memcpy(&user_sregs.fpregs, &current->thread.fp_regs,
-	       sizeof(s390_fp_regs));
+	       sizeof(user_sregs.fpregs));
 	if (__copy_to_user(sregs, &user_sregs, sizeof(_sigregs)))
 		return -EFAULT;
 	return 0;
@@ -82,8 +83,13 @@ static int restore_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
 	/* Alwys make any pending restarted system call return -EINTR */
 	current_thread_info()->restart_block.fn = do_no_restart_syscall;
 
-	if (__copy_from_user(&user_sregs, sregs, sizeof(_sigregs)))
+	if (__copy_from_user(&user_sregs, sregs, sizeof(user_sregs)))
 		return -EFAULT;
+
+	/* Loading the floating-point-control word can fail. Do that first. */
+	if (restore_fp_ctl(&user_sregs.fpregs.fpc))
+		return -EINVAL;
+
 	/* Use regs->psw.mask instead of PSW_USER_BITS to preserve PER bit. */
 	regs->psw.mask = (regs->psw.mask & ~PSW_MASK_USER) |
 		(user_sregs.regs.psw.mask & PSW_MASK_USER);
@@ -97,14 +103,13 @@ static int restore_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
 	regs->psw.addr = user_sregs.regs.psw.addr;
 	memcpy(&regs->gprs, &user_sregs.regs.gprs, sizeof(sregs->regs.gprs));
 	memcpy(&current->thread.acrs, &user_sregs.regs.acrs,
-	       sizeof(sregs->regs.acrs));
+	       sizeof(current->thread.acrs));
 	restore_access_regs(current->thread.acrs);
 
 	memcpy(&current->thread.fp_regs, &user_sregs.fpregs,
-	       sizeof(s390_fp_regs));
-	current->thread.fp_regs.fpc &= FPC_VALID_MASK;
+	       sizeof(current->thread.fp_regs));
 
-	restore_fp_regs(&current->thread.fp_regs);
+	restore_fp_regs(current->thread.fp_regs.fprs);
 	clear_thread_flag(TIF_SYSCALL);	/* No longer in a system call */
 	return 0;
 }

arch/s390/kvm/kvm-s390.c

@@ -343,10 +343,11 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
 
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
-	save_fp_regs(&vcpu->arch.host_fpregs);
+	save_fp_ctl(&vcpu->arch.host_fpregs.fpc);
+	save_fp_regs(vcpu->arch.host_fpregs.fprs);
 	save_access_regs(vcpu->arch.host_acrs);
-	vcpu->arch.guest_fpregs.fpc &= FPC_VALID_MASK;
-	restore_fp_regs(&vcpu->arch.guest_fpregs);
+	restore_fp_ctl(&vcpu->arch.guest_fpregs.fpc);
+	restore_fp_regs(vcpu->arch.guest_fpregs.fprs);
 	restore_access_regs(vcpu->run->s.regs.acrs);
 	gmap_enable(vcpu->arch.gmap);
 	atomic_set_mask(CPUSTAT_RUNNING, &vcpu->arch.sie_block->cpuflags);
@@ -356,9 +357,11 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	atomic_clear_mask(CPUSTAT_RUNNING, &vcpu->arch.sie_block->cpuflags);
 	gmap_disable(vcpu->arch.gmap);
-	save_fp_regs(&vcpu->arch.guest_fpregs);
+	save_fp_ctl(&vcpu->arch.guest_fpregs.fpc);
+	save_fp_regs(vcpu->arch.guest_fpregs.fprs);
 	save_access_regs(vcpu->run->s.regs.acrs);
-	restore_fp_regs(&vcpu->arch.host_fpregs);
+	restore_fp_ctl(&vcpu->arch.host_fpregs.fpc);
+	restore_fp_regs(vcpu->arch.host_fpregs.fprs);
 	restore_access_regs(vcpu->arch.host_acrs);
 }
 
@@ -618,9 +621,12 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
 
 int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
+	if (test_fp_ctl(fpu->fpc))
+		return -EINVAL;
 	memcpy(&vcpu->arch.guest_fpregs.fprs, &fpu->fprs, sizeof(fpu->fprs));
-	vcpu->arch.guest_fpregs.fpc = fpu->fpc & FPC_VALID_MASK;
-	restore_fp_regs(&vcpu->arch.guest_fpregs);
+	vcpu->arch.guest_fpregs.fpc = fpu->fpc;
+	restore_fp_ctl(&vcpu->arch.guest_fpregs.fpc);
+	restore_fp_regs(vcpu->arch.guest_fpregs.fprs);
 	return 0;
 }
 
@@ -876,7 +882,8 @@ int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu, unsigned long addr)
 	 * copying in vcpu load/put. Lets update our copies before we save
 	 * it into the save area
 	 */
-	save_fp_regs(&vcpu->arch.guest_fpregs);
+	save_fp_ctl(&vcpu->arch.guest_fpregs.fpc);
+	save_fp_regs(vcpu->arch.guest_fpregs.fprs);
 	save_access_regs(vcpu->run->s.regs.acrs);
 
 	if (__guestcopy(vcpu, addr + offsetof(struct save_area, fp_regs),

arch/s390/math-emu/math.c

@@ -19,6 +19,8 @@
 #include <math-emu/double.h>
 #include <math-emu/quad.h>
 
+#define FPC_VALID_MASK		0xF8F8FF03
+
 /*
  * I miss a macro to round a floating point number to the
  * nearest integer in the same floating point format.