alpha: unbreak osf_setsysinfo(SSI_NVPAIRS, [SSIN_UACPROC, UAC_SIGBUS])

The bug was accidentally found by the following program:

    #include <asm/sysinfo.h>
    #include <asm/unistd.h>
    #include <sys/syscall.h>
    static int setsysinfo(unsigned long op, void *buffer, unsigned long size,
                          int *start, void *arg, unsigned long flag) {
        return syscall(__NR_osf_setsysinfo, op, buffer, size, start, arg, flag);
    }

    int main(int argc, char **argv) {
        short x[10];
        unsigned int buf[2] = { SSIN_UACPROC, UAC_SIGBUS, };
        setsysinfo(SSI_NVPAIRS, buf, 1, 0, 0, 0);

        int  *y = (int*) (x+1);
        *y = 0;
        return 0;
    }

The program shoud fail on SIGBUS, but didn't.

The patch is a second part of userspace flag fix (commit 745dd240
"Alpha: Rearrange thread info flags fixing two regressions").

Deleted outdated out-of-sync 'UAC_SHIFT' (the cause of bug) in favour of
'ALPHA_UAC_SHIFT'.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Acked-by: Michael Cree <mcree@orcon.net.nz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/include/asm/sysinfo.h

@@ -27,13 +27,4 @@
 #define UAC_NOFIX			2
 #define UAC_SIGBUS			4
 
-
-#ifdef __KERNEL__
-
-/* This is the shift that is applied to the UAC bits as stored in the
-   per-thread flags.  See thread_info.h.  */
-#define UAC_SHIFT			6
-
-#endif
-
 #endif /* __ASM_ALPHA_SYSINFO_H */

arch/alpha/include/asm/thread_info.h

@@ -74,9 +74,9 @@ register struct thread_info *__current_thread_info __asm__("$8");
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_POLLING_NRFLAG	8	/* poll_idle is polling NEED_RESCHED */
 #define TIF_DIE_IF_KERNEL	9	/* dik recursion lock */
-#define TIF_UAC_NOPRINT		10	/* see sysinfo.h */
-#define TIF_UAC_NOFIX		11
-#define TIF_UAC_SIGBUS		12
+#define TIF_UAC_NOPRINT		10	/* ! Preserve sequence of following */
+#define TIF_UAC_NOFIX		11	/* ! flags as they match            */
+#define TIF_UAC_SIGBUS		12	/* ! userspace part of 'osf_sysinfo' */
 #define TIF_MEMDIE		13	/* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK	14	/* restore signal mask in do_signal */
 #define TIF_FREEZE		16	/* is freezing for suspend */
@@ -97,7 +97,7 @@ register struct thread_info *__current_thread_info __asm__("$8");
 #define _TIF_ALLWORK_MASK	(_TIF_WORK_MASK		\
 				 | _TIF_SYSCALL_TRACE)
 
-#define ALPHA_UAC_SHIFT		10
+#define ALPHA_UAC_SHIFT		TIF_UAC_NOPRINT
 #define ALPHA_UAC_MASK		(1 << TIF_UAC_NOPRINT | 1 << TIF_UAC_NOFIX | \
 				 1 << TIF_UAC_SIGBUS)
 

arch/alpha/kernel/osf_sys.c

@@ -42,6 +42,7 @@
 #include <asm/uaccess.h>
 #include <asm/system.h>
 #include <asm/sysinfo.h>
+#include <asm/thread_info.h>
 #include <asm/hwrpb.h>
 #include <asm/processor.h>
 
@@ -633,7 +634,8 @@ SYSCALL_DEFINE5(osf_getsysinfo, unsigned long, op, void __user *, buffer,
  	case GSI_UACPROC:
 		if (nbytes < sizeof(unsigned int))
 			return -EINVAL;
- 		w = (current_thread_info()->flags >> UAC_SHIFT) & UAC_BITMASK;
+		w = (current_thread_info()->flags >> ALPHA_UAC_SHIFT) &
+			UAC_BITMASK;
 		if (put_user(w, (unsigned int __user *)buffer))
 			return -EFAULT;
  		return 1;
@@ -756,8 +758,8 @@ SYSCALL_DEFINE5(osf_setsysinfo, unsigned long, op, void __user *, buffer,
  			case SSIN_UACPROC:
 			again:
 				old = current_thread_info()->flags;
-				new = old & ~(UAC_BITMASK << UAC_SHIFT);
-				new = new | (w & UAC_BITMASK) << UAC_SHIFT;
+				new = old & ~(UAC_BITMASK << ALPHA_UAC_SHIFT);
+				new = new | (w & UAC_BITMASK) << ALPHA_UAC_SHIFT;
 				if (cmpxchg(&current_thread_info()->flags,
 					    old, new) != old)
 					goto again;