s390/compat: correct uc_sigmask of the compat signal frame

commit 8d4bd0ed upstream.

The uc_sigmask in the ucontext structure is an array of words to keep
the 64 signal bits (or 1024 if you ask glibc but the kernel sigset_t
only has 64 bits).

For 64 bit the sigset_t contains a single 8 byte word, but for 31 bit
there are two 4 byte words. The compat signal handler code uses a
simple copy of the 64 bit sigset_t to the 31 bit compat_sigset_t.
As s390 is a big-endian architecture this is incorrect, the two words
in the 31 bit sigset_t array need to be swapped.
Reported-by: Stefan Liebler <stli@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[bwh: Backported to 3.2:
 - Introduce local compat_sigset_t in setup_frame32()
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/s390/kernel/compat_signal.c

@@ -52,6 +52,19 @@ typedef struct
 	__u32 gprs_high[NUM_GPRS];
 } rt_sigframe32;
 
+static inline void sigset_to_sigset32(unsigned long *set64,
+				      compat_sigset_word *set32)
+{
+	set32[0] = (compat_sigset_word) set64[0];
+	set32[1] = (compat_sigset_word)(set64[0] >> 32);
+}
+
+static inline void sigset32_to_sigset(compat_sigset_word *set32,
+				      unsigned long *set64)
+{
+	set64[0] = (unsigned long) set32[0] | ((unsigned long) set32[1] << 32);
+}
+
 int copy_siginfo_to_user32(compat_siginfo_t __user *to, siginfo_t *from)
 {
 	int err;
@@ -361,12 +374,14 @@ asmlinkage long sys32_sigreturn(void)
 {
 	struct pt_regs *regs = task_pt_regs(current);
 	sigframe32 __user *frame = (sigframe32 __user *)regs->gprs[15];
+	compat_sigset_t cset;
 	sigset_t set;
 
 	if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 		goto badframe;
-	if (__copy_from_user(&set.sig, &frame->sc.oldmask, _SIGMASK_COPY_SIZE32))
+	if (__copy_from_user(&cset.sig, &frame->sc.oldmask, _SIGMASK_COPY_SIZE32))
 		goto badframe;
+	sigset32_to_sigset(cset.sig, set.sig);
 	sigdelsetmask(&set, ~_BLOCKABLE);
 	set_current_blocked(&set);
 	if (restore_sigregs32(regs, &frame->sregs))
@@ -383,6 +398,7 @@ asmlinkage long sys32_rt_sigreturn(void)
 {
 	struct pt_regs *regs = task_pt_regs(current);
 	rt_sigframe32 __user *frame = (rt_sigframe32 __user *)regs->gprs[15];
+	compat_sigset_t cset;
 	sigset_t set;
 	stack_t st;
 	__u32 ss_sp;
@@ -391,8 +407,9 @@ asmlinkage long sys32_rt_sigreturn(void)
 
 	if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 		goto badframe;
-	if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
+	if (__copy_from_user(&cset, &frame->uc.uc_sigmask, sizeof(cset)))
 		goto badframe;
+	sigset32_to_sigset(cset.sig, set.sig);
 	sigdelsetmask(&set, ~_BLOCKABLE);
 	set_current_blocked(&set);
 	if (restore_sigregs32(regs, &frame->uc.uc_mcontext))
@@ -464,13 +481,16 @@ static int setup_frame32(int sig, struct k_sigaction *ka,
 			sigset_t *set, struct pt_regs * regs)
 {
 	sigframe32 __user *frame = get_sigframe(ka, regs, sizeof(sigframe32));
+	compat_sigset_t cset;
+
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(sigframe32)))
 		goto give_sigsegv;
 
 	if (frame == (void __user *) -1UL)
 		goto give_sigsegv;
 
-	if (__copy_to_user(&frame->sc.oldmask, &set->sig, _SIGMASK_COPY_SIZE32))
+	sigset_to_sigset32(set->sig, cset.sig);
+	if (__copy_to_user(&frame->sc.oldmask, &cset.sig, _SIGMASK_COPY_SIZE32))
 		goto give_sigsegv;
 
 	if (save_sigregs32(regs, &frame->sregs))
@@ -524,6 +544,7 @@ static int setup_frame32(int sig, struct k_sigaction *ka,
 static int setup_rt_frame32(int sig, struct k_sigaction *ka, siginfo_t *info,
 			   sigset_t *set, struct pt_regs * regs)
 {
+	compat_sigset_t cset;
 	int err = 0;
 	rt_sigframe32 __user *frame = get_sigframe(ka, regs, sizeof(rt_sigframe32));
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(rt_sigframe32)))
@@ -536,6 +557,7 @@ static int setup_rt_frame32(int sig, struct k_sigaction *ka, siginfo_t *info,
 		goto give_sigsegv;
 
 	/* Create the ucontext.  */
+	sigset_to_sigset32(set->sig, cset.sig);
 	err |= __put_user(UC_EXTENDED, &frame->uc.uc_flags);
 	err |= __put_user(0, &frame->uc.uc_link);
 	err |= __put_user(current->sas_ss_sp, &frame->uc.uc_stack.ss_sp);
@@ -544,7 +566,7 @@ static int setup_rt_frame32(int sig, struct k_sigaction *ka, siginfo_t *info,
 	err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
 	err |= save_sigregs32(regs, &frame->uc.uc_mcontext);
 	err |= save_sigregs_gprs_high(regs, frame->gprs_high);
-	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
+	err |= __copy_to_user(&frame->uc.uc_sigmask, &cset, sizeof(cset));
 	if (err)
 		goto give_sigsegv;