uaccess: add probe_kernel_write()

add probe_kernel_read() and probe_kernel_write().

Uninlined and restricted to kernel range memory only, as suggested
by Linus.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 50 insertions, 1 deletions

diff --git a/mm/Makefile b/mm/Makefile
index a5b0dd93427a..18c143b3c46c 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -8,7 +8,7 @@ mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
                            vmalloc.o
 
 obj-y                   := bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
-                           page_alloc.o page-writeback.o pdflush.o \
+                           maccess.o page_alloc.o page-writeback.o pdflush.o \
                            readahead.o swap.o truncate.o vmscan.o \
                            prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
                            page_isolation.o $(mmu-y)
diff --git a/mm/maccess.c b/mm/maccess.c
new file mode 100644
index 000000000000..24f81b971403
--- /dev/null
+++ b/mm/maccess.c
@@ -0,0 +1,49 @@
+/*
+ * Access kernel memory without faulting.
+ */
+#include <linux/uaccess.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+
+/**
+ * probe_kernel_read(): safely attempt to read from a location
+ * @dst: pointer to the buffer that shall take the data
+ * @src: address to read from
+ * @size: size of the data chunk
+ *
+ * Safely read from address @src to the buffer at @dst.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+long probe_kernel_read(void *dst, void *src, size_t size)
+{
+        long ret;
+
+        pagefault_disable();
+        ret = __copy_from_user_inatomic(dst,
+                        (__force const void __user *)src, size);
+        pagefault_enable();
+
+        return ret ? -EFAULT : 0;
+}
+EXPORT_SYMBOL_GPL(probe_kernel_read);
+
+/**
+ * probe_kernel_write(): safely attempt to write to a location
+ * @dst: address to write to
+ * @src: pointer to the data that shall be written
+ * @size: size of the data chunk
+ *
+ * Safely write to address @dst from the buffer at @src.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+long probe_kernel_write(void *dst, void *src, size_t size)
+{
+        long ret;
+
+        pagefault_disable();
+        ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
+        pagefault_enable();
+
+        return ret ? -EFAULT : 0;
+}
+EXPORT_SYMBOL_GPL(probe_kernel_write);