5 files changed, 28 insertions, 18 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 */
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index 6c79f1b44fe7..e0eaf11134b4 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -130,8 +130,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
         /* Verify that the to be replaced code matches what we expect. */
         if (memcmp(&orig, &old, sizeof(old)))
                 return -EINVAL;
-        if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))
-                return -EPERM;
+        s390_kernel_write((void *) rec->ip, &new, sizeof(new));
         return 0;
 }
 
@@ -159,8 +158,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
         /* Verify that the to be replaced code matches what we expect. */
         if (memcmp(&orig, &old, sizeof(old)))
                 return -EINVAL;
-        if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))
-                return -EPERM;
+        s390_kernel_write((void *) rec->ip, &new, sizeof(new));
         return 0;
 }
 
@@ -231,14 +229,16 @@ int ftrace_enable_ftrace_graph_caller(void)
 {
         u8 op = 0x04; /* set mask field to zero */
 
-        return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+        s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+        return 0;
 }
 
 int ftrace_disable_ftrace_graph_caller(void)
 {
         u8 op = 0xf4; /* set mask field to all ones */
 
-        return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+        s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+        return 0;
 }
 
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/s390/kernel/jump_label.c b/arch/s390/kernel/jump_label.c
index 830066f936c8..a90299600483 100644
--- a/arch/s390/kernel/jump_label.c
+++ b/arch/s390/kernel/jump_label.c
@@ -78,7 +78,7 @@ static void __jump_label_transform(struct jump_entry *entry,
                 if (memcmp((void *)entry->code, &old, sizeof(old)))
                         jump_label_bug(entry, &old, &new);
         }
-        probe_kernel_write((void *)entry->code, &new, sizeof(new));
+        s390_kernel_write((void *)entry->code, &new, sizeof(new));
 }
 
 static int __sm_arch_jump_label_transform(void *data)
diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index f516edc1fbe3..389db56a2208 100644
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -178,7 +178,7 @@ static int swap_instruction(void *data)
         }
 skip_ftrace:
         kcb->kprobe_status = KPROBE_SWAP_INST;
-        probe_kernel_write(p->addr, &new_insn, len);
+        s390_kernel_write(p->addr, &new_insn, len);
         kcb->kprobe_status = status;
         return 0;
 }
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index 2eb34bdfc613..fb737e9e0683 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -16,13 +16,7 @@
 #include <asm/ctl_reg.h>
 #include <asm/io.h>
 
-/*
- * This function writes to kernel memory bypassing DAT and possible
- * write protection. It copies one to four bytes from src to dst
- * using the stura instruction.
- * Returns the number of bytes copied or -EFAULT.
- */
-static long probe_kernel_write_odd(void *dst, const void *src, size_t size)
+static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
 {
         unsigned long count, aligned;
         int offset, mask;
@@ -48,19 +42,34 @@ static long probe_kernel_write_odd(void *dst, const void *src, size_t size)
         return rc ? rc : count;
 }
 
-long probe_kernel_write(void *dst, const void *src, size_t size)
+/*
+ * s390_kernel_write - write to kernel memory bypassing DAT
+ * @dst: destination address
+ * @src: source address
+ * @size: number of bytes to copy
+ *
+ * This function writes to kernel memory bypassing DAT and possible page table
+ * write protection. It writes to the destination using the sturg instruction.
+ * Therefore we have a read-modify-write sequence: the function reads four
+ * bytes from destination at a four byte boundary, modifies the bytes
+ * requested and writes the result back in a loop.
+ *
+ * Note: this means that this function may not be called concurrently on
+ *       several cpus with overlapping words, since this may potentially
+ *       cause data corruption.
+ */
+void notrace s390_kernel_write(void *dst, const void *src, size_t size)
 {
         long copied = 0;
 
         while (size) {
-                copied = probe_kernel_write_odd(dst, src, size);
+                copied = s390_kernel_write_odd(dst, src, size);
                 if (copied < 0)
                         break;
                 dst += copied;
                 src += copied;
                 size -= copied;
         }
-        return copied < 0 ? -EFAULT : 0;
 }
 
 static int __memcpy_real(void *dest, void *src, size_t count)