s390/maccess: remove potentially broken probe_kernel_write()

Remove the s390 architecture implementation of probe_kernel_write() and
instead use a new function s390_kernel_write() to modify kernel text and
data everywhere.

The s390 implementation of probe_kernel_write() was potentially broken
since it modified memory in a read-modify-write fashion, which read four
bytes, modified the requested bytes within those four bytes and wrote
the result back.
If two cpus would modify the same four byte area at different locations
within that area, this could lead to corruption.
Right now the only places which called probe_kernel_write() did run within
stop_machine_run. Therefore the scenario can't happen right now, however
that might change at any time.

To fix this rename probe_kernel_write() to s390_kernel_write() which can
have special semantics, like only call it while running within stop_machine().

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

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index cd4c68e0398d..d64a7a62164f 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -372,5 +372,6 @@ static inline unsigned long __must_check clear_user(void __user *to, unsigned lo
 }
 
 int copy_to_user_real(void __user *dest, void *src, unsigned long count);
+void s390_kernel_write(void *dst, const void *src, size_t size);
 
 #endif /* __S390_UACCESS_H */