s390/uaccess: shorten strncpy_from_user/strnlen_user

Always stay within page boundaries when copying from user within
strlen_user_mvcos()/strncpy_from_user_mvcos(). This allows to
shorten the code a bit and may prevent unnecessary faults, since
we copy quite large amounts of memory to kernel space.

Also directly call the mvcos variants of copy_from_user() to
avoid indirect branches.

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

1 files changed, 12 insertions, 12 deletions

diff --git a/arch/s390/lib/uaccess_mvcos.c b/arch/s390/lib/uaccess_mvcos.c
index 2443ae476e33..7f3eb3d56024 100644
--- a/arch/s390/lib/uaccess_mvcos.c
+++ b/arch/s390/lib/uaccess_mvcos.c
@@ -162,19 +162,19 @@ static size_t clear_user_mvcos(size_t size, void __user *to)
 
 static size_t strnlen_user_mvcos(size_t count, const char __user *src)
 {
+        size_t done, len, offset, len_str;
         char buf[256];
-        int rc;
-        size_t done, len, len_str;
 
         done = 0;
         do {
-                len = min(count - done, (size_t) 256);
-                rc = uaccess.copy_from_user(len, src + done, buf);
-                if (unlikely(rc == len))
+                offset = (size_t)src & ~PAGE_MASK;
+                len = min(256UL, PAGE_SIZE - offset);
+                len = min(count - done, len);
+                if (copy_from_user_mvcos(len, src, buf))
                         return 0;
-                len -= rc;
                 len_str = strnlen(buf, len);
                 done += len_str;
+                src += len_str;
         } while ((len_str == len) && (done < count));
         return done + 1;
 }
@@ -182,18 +182,18 @@ static size_t strnlen_user_mvcos(size_t count, const char __user *src)
 static size_t strncpy_from_user_mvcos(size_t count, const char __user *src,
                                       char *dst)
 {
-        int rc;
-        size_t done, len, len_str;
+        size_t done, len, offset, len_str;
 
         done = 0;
         do {
-                len = min(count - done, (size_t) 4096);
-                rc = uaccess.copy_from_user(len, src + done, dst);
-                if (unlikely(rc == len))
+                offset = (size_t)src & ~PAGE_MASK;
+                len = min(count - done, PAGE_SIZE - offset);
+                if (copy_from_user_mvcos(len, src, dst))
                         return -EFAULT;
-                len -= rc;
                 len_str = strnlen(dst, len);
                 done += len_str;
+                src += len_str;
+                dst += len_str;
         } while ((len_str == len) && (done < count));
         return done;
 }